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thesis entitled

TEMPERATURE AND DAILY LIGHT INTEGRAL EFFECTS
ON FIVE BEDDING PLANT SPECIES

presented by

Lee Ann Pramuk

has been accepted towards fulﬁllment
of the requirements for the

MS. degree in Horticulture

 

 

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6/01 c:/ClRC/DateDue.p65-p. 1 5

TEMPERATURE AND DAILY LIGHT INTEGRAL EFFECTS ON FIVE BEDDING
PLANT SPECIES

By

Lee Ann Pramuk

A THESIS

Submitted to Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

2003

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ABSTRACT
TEMPERATURE AND DAILY LIGHT INTEGRAL EFFECTS ON FIVE BEDDING
PLANT SPECIES
By
Lee Ann Pramuk

Production of bedding plants is of major economic importance to the ﬂoriculture
industry, with >$1.7 billion wholesale value in the United States. Quantifying how
temperature and daily light integral (DLI) inﬂuence production of these crops would
enable greenhouse growers to improve the accuracy of scheduling crops, as well as
identify optimum environments for efﬁcient production. A series of experiments was
performed on ﬁve popular bedding plant species, Celosia argentea var. plumosa
‘Gloria Mix’, Impatiens wallerana ‘Accent Red’, Salvia splendens ‘Vista Red’, T agetes
patula ‘Bonanza Yellow’, and Viola xwittrockiana ‘Crystal Bowl Yellow’, to determine
the effects of temperature and DLI on growth and development during seedling and
ﬁnish stages. Increasing DLI during the plug stage (from 4.1 to 14.2 mol-m'zod")
increased initial plug quality (dry weight per node), and decreased subsequent time to
ﬂower. Models relating temperature (from 14 to 27 °C) and DLI (from 4 to 26 mol-m‘
2d“) to time to ﬁnished plug and ﬂowering were developed. For example, as
temperature increased from 14 to 27 °C, Tagetes time to ﬂowering decreased by 18
days under 5 mol-m‘Z-d'l and by 12 days under 25 mol-m‘z-d". Effects of temperature
and DLI on ﬂower size, ﬂower number, dry weight, node number, and height were

also quantiﬁed.

DEDICATION
In memory of Ronald Pramuk.
Your love and support are with me still.
Your courage, bravery, and love of life taught me volumes.
Each day, let us make a beautiful and great memory, as if it were to be the last we’ll

ever share.

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ACKNOWLEDGEMENTS

To my major professor, Dr. Erik Runkle, I extend my sincere thanks and
appreciation for guidance, support, and advice. To my other committee members, Dr.
Jeff Andresen and Dr. Royal Heins, I thank you for your valuable insight and guidance.

Also, I wish to thank the greenhouse growers who support Michigan State
ﬂoriculture research and the Michigan Agriculture Experiment Station for ﬁnancial
assistance. A special thank you to Allen Pyle and Raker’s Acres for plant material and
advice.

I extend a special thank you to the ﬂoriculture greenhouse technicians, Dave
J oeright and Mike Olrich for their assistance in experimental setup and for always
providing much needed laughter and singing. Thank you to Matt Steinkopf for
assistance in data collection and always making me smile. To my fellow graduate
students and ofﬁcemates, Grete Waaseth, Janelle Glady, Roberto Lopez, Marcus Duck,
and Charlie Rohwer, thanks for helping to make work an interesting and enjoyable
place. To my roommate and best buddy, Ann, thank you for keeping me grounded.

A big thank you to my family, Mom, Matt, Kris, Dave, Angie, Jim, and
Abigail. Your support and love are an inspiration and I couldn’t have made it without

you!

The

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TABLE OF CONTENTS

Page

LIST OF TABLES ................................................................................. vii

LIST OF FIGURES ............................................................................... viii

Literature Review .................................................................................... 1

Introduction ..................................................................................... 2

Temperature Effects on Plant Growth and Development ............................... 4

Vegetative Development and Temperature ....................................... 9

Flowering ............................................................................ l 1

Temperature Effects on Plant Quality ........................................... 12

Branching ................................................... . ................. 12

Flower Number .............................................................. 13

Flower Size ................................................................... 14

Plant Mass .................................................................... 15

Plant Height ................................................................... 16

Light Integral Effects on Growth and Development ...................... . ............ 17

Rate of Flower Development and DLI ......................................... 18

Plant Quality and DLI ........... . ................................................. 21

Plant Height .................................................. . ................ 22

Branching ..................................................................... 22

Dry Weight .......................... _ ........................................ 22

Flower Size and Number ......... . ................... . ..................... 23

Interaction of Temperature and Light Intensity ......................................... 24

Floral Development Rate ......................................................... 24

Height and Shoot number ......................................................... 26

Plant mass ............................................................................ 27

Leaf Unfolding Rate ................................................................ 30

Photothermal ratio .................................................................. 30

Literature Cited .............................................................................. 32

The Effects of Temperature and Daily Light Integral on Bedding Plant Plug Growth and

Development .................................................................................. 37

Introduction ................................................................................... 39

Materials and Methods ...................................................................... 41

Results ......................................................................................... 43

Discussion ..................................................................................... 45

Literature Cited .............................................................................. 48
Quantifying the Effects of Temperature and Daily Light Integral on Finish Bedding

Plant Growth and Development ........................................................... 71

Introduction ................................................................................... 73

Materials and Methods ...................................................................... 74

Results ......................................................................................... 77

Discussion ..................................................................................... 80

Literature Cited .............................................................................. 86
Effects of Daily Light Integral on Bedding Plant Plugs and Subsequent Growth and
Development ................................................................................. 1 1 1
Introduction .......................................... . . . . .. .......... . ........................ 1 13
Materials and Methods ..................................................................... 115
Results ........................................................................................ 1 18
Discussion .................................................................................... 120
Literature Cited ............................................................................. 124

vi

 

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LIST OF TABLES

SECTION I
Page
Table 1. Quantitative growth and developmental information for various ﬂoricultural
Plant ................................................................................................. 4
SECTION H
Table 1. Actual temperature recorded in greenhouse sections ............................. 49
Table 2. Actual daily light integral (DLI) recorded in greenhouse sections. ........... 49

Table 3. Signiﬁcance of temperature (T), daily light integral (DLI), and their
interaction (T*DLI) to the models developed for Celosia, Impatiens, Salvia, and
T agetes at ﬁnish. ............................................... .. ............................. 50

SECTION 111
Table 1. Air temperature and average shoot-tip temperature of plants (T ageles) under
ambient light treatments grown in glass greenhouses at the indicated setpoints. .. 87
Table 2. Daily light integral (DLI) under treatments. ....... .. .............................. 87
Table 3. Parameters of regression analysis relating rate of progress to ﬂower, height,
dry weight, node number, ﬂower number, and ﬂower size for Celosia, Impatiens,
Salvia, and T agetes to temperature (T) in °C and daily light integral (DLI) in mol
m’2 d". .......................................................................................... 87
Table 4. Theoretical example of the cost of supplying an additional 5 mol-m‘z-d'l of
HPS lighting to Celosia grown at 20 °C. Financial information and assumptions
taken from Fisher and Donnelly, 2002. ................................................. 89

SECTION IV
Table 1. Actual environmental conditions inside growth chambers with three daily light
integral (DLI) treatments. LL=low light, ML= moderate light, HL= high light,
VPD= vapor pressure deﬁcit. ............................................................ 126
Table 2. Comparison of canopy and air temperatures (°C) during a 24-h period in
growth chambers. ........................................................................... 126
Table 3. The effect of daily light integral (DLI) during the plug stage on node number
at time of transplant (n= 16) and on subsequent ﬂower size. ........................ 127

vii

 

Fi

Fr

Fig

Fig

LIST OF FIGURES

Page
SECTION I
Figure 1. A model relating rate of development as a linear function of temperature...3
Figure 2. Average daily light integral in East Lansing, MI and Phoenix, AZ outside
and inside a typical greenhouse .................................................................. 17

SECTION II
Figure 1. Response surface for Celosia days to ﬁnish as a function of average daily
temperature (T) and average daily light integral (DLI). Celosia was considered to
be ﬁnished when the plug was at the fourth leaf stage and reached 3.5 cm in
width. The equation for the response surface was y = 111.901 - 3.25716T -
1.41259DLI + 0.04514T*DLI with R2 = 0.96 ............... . ........................ 51
Figure 2. Response surface for Celosia dry weight as a function of average daily
temperature (T) and average daily light integral (DLI). The equation for the
response surface was y = -0.19702 + 0.01817T + 0.00749DLI - 0.00037254T2 -
0.00023343T*DLI with R2 = 0.54. ..................................................... 52
Figure 3. Response surface for Celosia height as a function of average daily
temperature (T) and average daily light integral GDLI). The equation for the
response surface was y = 2. 50443 + 0. 13542DLI + 0. 00342T2 + 0. 00223DLI-
O. OO951T*DLI with R2 = 0.17. ......................................................... 53
Figure 4. Response surface for Celosia node number at ﬁnish as a function of average
daily temperature (T) and average daily light integral (DLI). The equation for the
response surface was y— = 29 329- 1.75315T + 0. 25702DII + 0. 03216T2-

0. 00865T*DLI with R2 = 0.65. ......................................................... 54
Figure 5. The inﬂuence of temperature and daily light integral (DLI) on visible bud
percentage at the ﬁnish plug stage in Celosia ........................................... 55

Figure 6. Response surface for Impatiens days to ﬁnish as a function of average daily
temperature (T) and average daily light integral (DLI). The equation for the
response surface was y = 185.41233 - 11.27041T - 1.53677DLI + 0.20366T2 +
0.05670T*DLI with R2 = 0.96. .......................................................... 56

Figure 7. Response surface for Impatiens dry weight at ﬁnishas a function of average
daily temperature (T) and average daily light integral (DLI). The equation for the
response surface was y = 0.10154 - 0.00651T + 0.00245DLI + 0.0001202T2 -
0.00005133DLI2 with R2 = 0.39. ........................................................ 57

Figure 8. Response surface for Impatiens height at ﬁnishas a function of average daily
temperature (T) and average daily light integral (DLI). The equation for the
response surface was y = 5.896504 - 0.421892T + 0.065601DLI + 0.014178T2
+ 0.002082DLI2 - 0.007713T*DLI with R2 = 0.39. ................................. 58

Figure 9. Response surface for Impatiens node number at fmish as a function of
average daily temperature (T) and average daily light integral (DLI). The

viii

 

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equation for the response surface was y = -4.54 + 0.82677T + 0.24486DLI -

0.01542T2 - 0.00786T*DLI with R2 = 0.31 ............................................ 59
Figure 10. The inﬂuence of average daily temperature (T) and average daily light
integral (DLI) on visible bud percentage at ﬁnish in Impatiens. .................... 60

Figure 11. The inﬂuence of temperature on days to ﬁnished plug in Salvia. Daily light
integral (DLI) did not have a signiﬁcant effect on days to ﬁnished plug. Plugs
were considered ﬁnished when the second leaf pair reached 3.5 cm in width. 61
Figure 12. Response surface for Salvia dry weight at ﬁnish as a function of average
daily temperature (T) and average daily light integral (DLI). The equation for the
response surface was y = 0.057617 - 0.004011T + 0.004607DLI +
- 0.000095013T2 - 0.000026618DL12- 0.000108T*DLI with R2 = 0.60. ........... 62
Figure 13. Response surface for Salvia height at ﬁnish as a function of average daily
temperature (T) and average daily light integral (DLI). The equation for the
response surface was y = 1.761064 - 0.081501T + 0.158651DLI +
0.009023T+ 0.002123DLI2 - 0.012233T*DLI with R2 = 0.55. ................... 63
Figure 14. Response surface for Salvia node number at ﬁnish as a function of average
daily temperature (T) and average daily light integral (DLD. The equation for the
response surface was y = 6.85962 - 0.30447T + 0.00538T2 - 0.00095188DLI2

+0.00332T*DLI with R2 = 0.39 ......................................................... 64
Figure 15. The inﬂuence of temperature and daily light integral (DLI) on visible bud
percentage at the ﬁnish plug stage in Salvia. ........................................... 65

Figure 16. The inﬂuence of temperature on days to ﬁnished plug in T agetes. Daily
light integral (DLI) did not have a signiﬁcant effect on day to ﬁnished plug.
Plugs were considered ﬁnished when the second leaf pair reached 4.5 cm in
width. .......................................................................................... 66
Figure 17. Response surface for T agetes dry weight at ﬁnishas a function of average
daily temperature (T) and average daily light integral (DLI). The equation for the
response surface was y = 0.05653 -- 0.00460T + 0.00587DLI + 0.0001162sz-
0.00017692T*DLI with R2 = 0.60. ...................................................... 67
Figure 18. Response surface for T agetes height at ﬁnish as a function of average daily
temperature (T) and average daily light integral (DLI). The equation for the
response surface was y = 4.85607 - 0.21798’I‘ + 0.08484DLI + 0.00802T2 -
0.000306T*DLI with R2 = 0.46. ......................................................... 68
Figure 19. Response surface for T agetes node number at ﬁnish as a function of
average daily temperature (T) and average daily light integral (DLI). Each point
may represent more than one observation. The equation for the response surface
was y = 4.79135 - 0.16583T+ 0.00355T2 + 0.01463DLI with R2 = 0.10. 69
Figure 20. The inﬂuence of temperature and daily light integral (DLI) on visible bud
percentage at the ﬁnish plug stage in T agetes. ......................................... 70

SECTION IH
Figure 1. Temperature and daily light integral effects on Celosia rate of progress
toward ﬂowering. The model was generated using the coefﬁcients in Table 3. . 90

Figure 2. Temperature and daily light integral (DLI) effects on Celosia height at
ﬂowering. The model was generated using the coefﬁcients in Table 3. .......... 91

Figure 3. Temperature and daily light integral (DLI) effects on Celosia dry weight at
ﬂowering. The model was generated using the coefﬁcients in Table 3. .......... 92

Figure 4. Temperature and daily light integral (DLI) effects on Celosia node number at
ﬂowering. The model was generated using the coefﬁcients in Table 3. .......... 93

Figure 6. Frequency of predicted minus actual days to ﬂower in Celosia and
Impatiens. The total number of plants observed under temperatures ranging from
14 to 26 °C and daily light integrals from 4 to 26 mol-m‘Z-d" was 296 and 298,

respectively. .................................................................................. 95
Figure 5. Temperature and daily light integral (DLI) effects on Celosia ﬂower number.
The model was generated using the coefﬁcients in Table 3. ......................... 95

Figure 7. Temperature and daily light integral (DLI) effects on Impatiens rate of
progress toward ﬂowering. The model was generated using the coefﬁcients in

Table 3 ........................................................................................ 96
Figure 8. Temperature and daily light integral (DLI) effects on Impatiens height at
ﬂowering. The model was generated using the coefﬁcients m Table 3. ........... 97
Figure 9. Temperature and daily light integral (DLI) effects on Impatiens dry weight at
ﬂowering. The model was generated using the coefﬁcients in Table 3. .......... 98
Figure 10. Temperature and daily light integral (DLI) effects on Impatiens ﬂower size.
. The model was generated using the coefﬁcients in Table 3. ......................... 99
Figure 11. Temperature and daily light integral (DLI) effects on Impatiens ﬂower
number. The model was generated using the coefﬁcients in Table 3. ............ 100

Figure 12. Temperature and daily light integral (DLI) effects on Salvia rate of progress
toward ﬂowering. The model was generated using the coefﬁcients in Table 3. .101
Figure 13. Temperature and daily light integral (DLI) effects on Salvia height at
ﬂowering. The model was generated using the coefﬁcients in Table 3. ......... 102
Figure 14. Temperature and daily light integral (DLI) effects on Salvia dry weight at
ﬂowering. The model was generated using the coefﬁcients in Table 3. ......... 103
Figure 15. Temperature and daily light integral (DLI) effects on Salvia ﬂower number.
The model was generated using the coefﬁcients in Table 3. ........................ 104
Figure 16. Frequency of predicted minus actual days to ﬂower in Salvia and Tagetes.
The total number of plants observed under temperatures ranging from 14 to 26 °C
and daily light integrals from 4 to 26 mol~m’2-d'l was 300 and 292, respectively.

................................................................................................. 105
Figure 17. Temperature and daily light integral (DLI) effects on T agetes rate of
progress toward ﬂowering. The model was generated using the coefﬁcients in
Table 3 ........................................................................................ 106
Figure 18. Temperature and daily light integral (DLI) effects on T agetes height. The
model was generated using the coefﬁcients in Table 3. .............................. 107
Figure 19. Temperature and daily light integral (DLI) effects on T agetes dry weight.
The model was generated using the coefﬁcients in Table 3. ........................ 108
Figure 20. Temperature and daily light integral (DLI) effects on T agetes ﬂower size.
The model was generated using the coefﬁcients in Table 3. ........................ 109

 

 

 

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Figure 21. Temperature and daily light integral (DLI) effects on T agetes ﬂower
number. The model was generated using the coefﬁcients in Table 3. ............. 110

SECTION IV

Figure 1. Relationships between daily light integral and average dry weight per average
node number as observed in Celosia, Impatiens, Salvia, T agetes, and Viola at
time of seedling transplant. Each symbol represents the averages of 16 plants.
Equations for regression lines are presented with corresponding r2 values. ...... 128

Figure 2. Relationship between daily light integral and average height (cm) as observed
in Celosia, Impatiens, Salvia, and Tagetes at time of transplant. L= linear and
Q: quadratic. NS, *,*** Nonsigniﬁcant or signiﬁcant at P S 0.05 or 0.001,
respectively. Equations for regression lines are presented with corresponding r2

values. ........................................................................................ 130
Figure 3. The relationship between DLI and percent visible ﬂower bud at transplant in
Impatiens and Tagetes. .................................................................... 132

Figure 4. The effect of daily light integral during the plug stage on subsequent days to
ﬂower, node number, ﬂower number, dry weight (g), and height (cm) in Celosia.
Error bars represent 95% conﬁdence intervals. L= linear and Q: quadratic.
NS,*** Nonsigniﬁcant or signiﬁcant at P S 0.001, respectively. Equations for
regression lines are presented with corresponding r2 values. ....................... 133

Figure 5. The effects of daily light integral during the plug stage on subsequent days to
ﬂower, node number, ﬂower number, dry weight (g), and height (cm) in
Impatiens. Error bars represent 95 % conﬁdence intervals. L= linear and Q:
quadratic. NS, *, *** Nonsigniﬁcant or signiﬁcant at P S 0.05, 0.001,
respectively Equations for regression lines are presented with corresponding 1'2
values. ...................................................................................... 135

Figure 6. The effects of daily light integral during the plug stage on subsequent days to
ﬂower, node number, ﬂower number, dry weight (g), and height (cm) in Salvia.
Error bars represent 95% conﬁdence intervals. L= linear and Q: quadratic.

NS, *** Nonsigniﬁcant or signiﬁcant at P S 0.001. Equations for regression lines
are presented with corresponding r2 values. ........................................... 137

Figure 7. The effects of daily light integral (DLI) during the plug stage on subsequent
days to ﬂower, node number, ﬂower number, dry weight (g), and height (cm) in
T agetes. Error bars represent 95% conﬁdence intervals. L= linear and Q:
quadratic. NS, *, **, *** Nonsigniﬁcant or signiﬁcant at P S 0.05, 0.01, or
0.001, respectively. Equations for regression lines are presented with
corresponding r2 values. ................................................................... 139

Figure 8. The effects of daily light integral during the plug stage on subsequent days to
ﬂower, node number, ﬂower number, dry weight (g), and height (cm) in Viola.
Error bars represent 95% conﬁdence intervals. L= linear and Q: quadratic.

NS, **, *** Nonsigniﬁcant or signiﬁcant at P S 0.01 or 0.001, respectively.
Equations for regression lines are presented along corresponding r2 values. ....141

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Figure 9. The effects of daily light integral during the plug stage on subsequent dry
weight gain per day to ﬂower in Celosia, Impatiens, Salvia, and T agetes. Error
bars represent 95% conﬁdence intervals. L= linear and Q: quadratic. NS, **,
*** Nonsigniﬁcant or signiﬁcant at P S 0.01 or 0.001 , respectively. Equations
for regression lines are presented with corresponding r2 values. ................... 143

xii

SECTION I

Literature Review

 

 

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Introduction

Production of garden plants is of major economic importance to the ﬂoriculture
industry. In 2000, greenhouse growers in the United States produced garden plants
with a wholesale value of $2.12 billion, representing 50% of the wholesale value of all
reported ﬂoricultural crops GISDA, 2001). At the state level, Michigan ranked third in
sales of wholesale ﬂoriculture products in 2000, only after California and Florida. In
Michigan, 726 growers reported gross sales greater than $10,000, and their estimated
collective wholesale value was $301 million for all surveyed ﬂoriculture crops. Of the
$301 million, $148 million was attributed to the sale of garden plants (MDA, 2001).

The production of spring bedding plants in relatively cold climates like
Michigan forces growers to rely on greenhouse heating in the winter and early spring.
In recent years, fuel prices have ﬂuctuated dramatically. For example, prices of natural
gas in 2000 and early 2001 were at record high levels due to a large increase in demand
without a corresponding increase in supply. In 1990, the average price of natural gas
sold to commercial consumers was $6.52 per thousand cubic feet (adjusted for
inﬂation), and in September 2001, the average price was $8.99 per thousand cubic feet
(EIA, 1999; EIA, 2001). In response to energy expenses, some growers have lowered
their thermostats to reduce their monthly heating bills; others have used supplemental
photosynthetic lighting in combination with lower temperature set points. Although
these methods could save in short-term fuel costs, crop timing and plant quality may be
compromised in the process. Crop timing is of paramount importance for growers
because many ﬂoricultural products are only marketable within narrow time frames.

For example, Easter lilies (Lilium longiﬂorum Thunb.) are sold during the 10—day

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period before Easter, and afterward, there is no demand for the crop. Plant quality is
important because it often determines the value and marketability of the crop.

Due to the value of bedding plants and the need for energy efﬁcient production,
the growth and development of bedding plants as a function of environmental variables
must be well understood and quantiﬁed. The effects of temperature and light intensity
have been studied on some economically important ﬂoricultural crops, such as petunia
(Petunia xhybrida Hort.Vilm.—Andr.), pansy (Viola xwittrockiana Gams.), vinca
(Catharanthus roseus L.), and seed geranium (Pelargonium xhortorum Bailey) (Adams
et al., 1997; 1999; Armitage et al., 1981; Pietsch et al., 1995). Although these studies
provide information on plant response to temperature and light, more research in this
area is warranted due to the variability of optimum temperatures and light requirements
among species and between developmental processes. For example, optimum
temperature for shortest time to ﬂower of pansy is 21.7 °C, but it is ~35 °C for vinca
(Adams et a1. , 1997; Pietsch et al., 1995). An example of the variability of optimum
temperature between developmental processes is observed in vinca; the optimum
temperature for ﬂower size is 25 °C, while the optimum temperature for leaf unfolding
and stem elongation is about 35 °C (Pietsch et al., 1995). Additionally, to our
knowledge, few scientiﬁc studies on temperature and irradiance interaction have been
published on other economically important ﬂoricultural crops, such as impatiens

(Impatiens wallerana Hook.f.) and marigold (Tagetes patula L.).

 

 

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Temperature Effects on Plant Growth and Development

Plant growth rate and morphological development are highly regulated by
temperature. Each plant species responds to a different set of temperatures, a minima,
maxima, and optima, called the cardinal temperatures. Growth rate is zero at or below
the base temperature, Tb, and is maximal at the optimum temperature, Tom. Growth
stops at some maximum temperature, Tm, and beyond that temperature plant death may
result (Fig.1). Between Tb and Top, the rate of plant development is typically assumed
to be linear (Salisbury and Ross, 1992). The values of Tb, Top, and Tmax are all species

speciﬁc. Examples are listed in Table 1.

 

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Temperature

Figure 1. A model relating rate of development as a linear function of temperature.

Many chemical processes occur simultaneously in a plant, each having its own
optimal temperature. The factor by which a reaction increases with a 10 °C increase in
temperature is called the Q10. For example, the Qlo for respiration of hybrid geranium

leaves is about 2.2, determined between 17 and 27 0C (Armitage et al., 1981). Thus,

 

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for g

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differ
study
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Low:
10 to
Warn

Vege

Way 1
nUmt

Unfol

for geranium leaves, the reaction rate of respiration approximately doubles for an
interval of 10 °C.

Tissues within the same plant may respond to temperatures differently because
different chemical processes have unique optimal temperatures. A classic example is a
study by Julius Van Sachs in 1863. He demonstrated differing optimal temperatures for
upper and lower tepal growth of tulips (T ulipa sp. L.) and crocus (Crocus sp. L.)
Lower tepal growth was optimal at 3 to 7 °C while upper tepal growth was greatest at
10 to 17 °C. This allows the ﬂowers to close at cooler temperatures and open at
warmer temperatures (Salisbury and Ross, 1992).

Vegetative Development and Temperature

The rate of vegetative development increases with increasing temperature. One
way to quantify vegetative development is by the leaf unfolding rate. This is the
number of leaves that unfold per unit of time, for example leaves-d". Knowing the leaf
unfolding rate of a species can help time crops to meet speciﬁc ﬁnish dates.

In many species, as average temperature increases, leaf unfolding rate increases
in a linear fashion until Tm, is reached (Moe and Heins, 1990). For example, this
relationship is observed in hibiscus (Hibiscus rosa-sinensis L. ‘Brilliant Red’ and ‘Pink
Versicolor’) (Karlsson et al. , 1990). A linear function approximated the leaf unfolding
response from 11 °C to 30 °C, and maximum leaf unfolding occurred at 32 °C with
0.229 leaves per day; beyond this point, leaf unfolding decreased (Karlsson et al. ,

1990). There was no difference in leaf unfolding rate for the two cultivars of hibiscus

(Karlsson et al. , 1990). Also, the leaf unfolding model was validated with three other
cultivars, ‘Florida Sunset’, ‘Painted Lady’, and ‘Euterpe’. Similar linear responses
have been observed in Chrysanthemum, easter lily, and vinca (Karlsson et al.,
1989,1988; Pietsch et al., 1995).

Karlsson (1992) studied the leaf unfolding rate in hiemalis begonia (Begonia
xhiemalis, ‘Hilda’ and ‘Ballet’). Long days promoted vegetative growth and short days
induced reproductive growth (Karlsson, 1992). Under long days, both cultivars had
similar unfolding rates when grown at 13 to 28 °C, with maximum leaf unfolding of
0.116 leaves-d‘l at 21 °C. A quadratic function was used to describe the 16-h long day
leaf unfolding rate. Under IO-h short days ‘Ballet’ continued to unfold at the same rate
as under 16—h long day conditions, but ‘Hilda’ decreased to half the rate observed under
long day conditions, illustrating differing cultivar responses to photoperiod.

Leaf unfolding rate has also been determined for poinsettia (Euphorbia
pulcherrima Willd. ex Klotzsch ‘Annette Hegg Dark Red’). Because poinsettias are
grown vegetatively before ﬂower initiation, Berghage et al. (1990) modeled leaf
unfolding rate from the time of pinching to the appearance of the ﬁrst three leaves
(LAG) and also the subsequent leaf unfolding rate (LUR). LAG was negatively
correlated with temperature; as average temperature increased from 18 °C to 29 °C,
LAG decreased by approximately 7 days. Subsequent leaf unfolding rate ranged from
0.132 leaves-d’1 with an average daily temperature (ADT) of 15.3 °C to 0.245 leaves-d'l
with an ADT of 27.8 °C. Day and night temperatures had equivalent effects on

poinsettia in both LAG and LUR (Berghage et al., 1990).

10

 

 

 

 

Flow

contri
develi
bud s

variat

(Perm
an opl
photo]
devek

increa

Chrys;
devek
ViSlbIc

al., 1g

Flowering

Because ﬂower organogenesis and development are largely under metabolic
control, the importance of temperature at this stage is basic to the rate of ﬂower
development for all bedding plants (Armitage, 1994). Thus, when plants reach visible
bud stage, ﬂowering is controlled by temperature more than any other environmental
variable (Armitage, 1994).

Kacsperski et al. (1991) showed that the number of days to ﬂower for petunia
(Petunia xhybrida ‘Snow Cloud’) was a quadratic function of average temperature with
an optimum temperature of 25 °C when grown under 13 mol-m'Z-d'l and an 18-h
photoperiod. In vinca, average daily temperature controlled days to ﬂower and ﬂower
development rate; time to ﬂower decreased by 30 days as average daily temperature
increased from 18 to 35 oC (Pietsch et al., 1995).

Different phases of ﬂowering can also have different optimum temperatures. In
Chrysanthemum ‘Bright Golden Anne’ (Dendranthema grandzﬂora Tzvelev.), four
developmental stages were studied: (1) from start of short days to visible bud, (2)
visible bud to disbud, (3) disbud to ﬁrst color, and (4) ﬁrst color to ﬂower (Karlsson et
al., 1989). Optimum temperatures for these stages were 21.3, 20.3, 23.1, and 19.1 °C,
respectively. Additionally, plants may exhibit temperature conditioning; the
temperature the plant receives in initial stages of development may inﬂuence subsequent
stages of development. Temperature extremes of 10 or 30 °C during the ﬁrst and

second stage of development of Chrysanthemum delayed the time to complete the third

11

"I

 

 

 

stage
tempt

Temr

plant.
are br

Bram

Gener
growr
0C (13)
brand
and K.
COoler
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branch
primal“.

(6108.

stage of develOpment. However, the fourth stage was unaffected by initial unfavorable
temperatures (Karlsson et al., 1989).
Temperature Effects on Plant Quality

Temperature profoundly affects plant quality, or the aesthetic appeal of the
plant. Some quantiﬁable indicators of plant quality that are affected by temperature
are branching, ﬂower number, ﬂower diameter, and plant biomass.

Branching

One characteristic of high quality plants is desirable plant architecture.
Generally, plants grown at cooler temperatures exhibit more branching than those
grown at warmer temperatures. For example, petunia ‘Snow Cloud’ grown at a 27 i3
°C day temperature (DT) and 7 °C night temperature (NT) had four more basal
branches 75 days after seed sow than those grown at 27 i3 °C DT/18 °C NT (Merritt
and Kohl, 1989). However, ﬂowering was delayed by 10 days when grown at the
cooler NT (Merritt and Kohl, 1989). Kaczperski et al. (1991) demonstrated that the
number of lateral shoots at ﬂowering formed by petunia ‘Snow Cloud’ decreased
quadratically as day temperature increased; as average temperature increased from 10
°C to 30 °C, the number of lateral shoots decreased from ~85 to z3.

Although research has shown that cooler temperatures can promote lateral
branching, short exposures to very high temperatures after pruning can suppress
primary shoot growth and promote lateral shoot growth. Higuchi et al. (1987) explored
the relationship between the duration of high temperature exposure, greater than 45 °C

(6 to 8 °C higher than the ambient control conditions), and the promotion of lateral

12

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shoot growth in salvia (Salvia splendens F. Sellow ex Roem. & Schult. ‘St. John’s
Fire’) and impatiens (Impatiens sultanii Hook. f. ‘Super Elﬁn Blush’) after pruning.
After 4 weeks, high-temperature treated salvia primary shoots were z57% shorter than
control plants. Lateral shoot growth increased in salvia and impatiens; maximum
growth of lateral shoots was attained at 850 °C x hour of high temperature for salvia
and 400 °C x hour for impatiens, when expressed as integrated temperature above 30 °C
(Higuchi et al. , 1987). Also, in salvia, the percentage of ﬂowering shoots under high
temperatures increased from 40 to 62% and the mean length of the inﬂorescence
increased from 5 to 11 cm measured 65 days after pruning as compared to the control
(Higuchi et al., 1987).
Flower Number

A large number of ﬂowers generally make plants more attractive to the
consumer, and thus potentially more valuable. In seed impatiens, ﬂower number, when
recorded after 4 weeks in temperature treatments, was lower at cooler temperatures (24
°C DT/18 °C NT) than at higher temperatures (30/24 °C DT/NT and 35/30 °C DT/NT)
due to slower bud development and opening rates at the cooler temperatures, indicating
a thermal time relationship (Lee et al., 1990). For example, Impatiens ‘Accent Pink’
had 50 and 48 ﬂowers in the higher temperature treatments, and 24 ﬂowers in the lower
temperature treatment (Lee et al., 1990). Other impatiens cultivars, such as ‘Accent
Rose’, ‘Dazzler Pink’, and ‘Super Elﬁn Rose’ exhibited similar results.

Flower bud number at ﬁrst ﬂowering of coreopsis (Coreopsis grandiﬂora Hogg

ex Sweet. ‘Sunray’), rudbeckia (Rudbeckia fulgida Ait. ‘Goldsturm’), and Shasta daisy

13

,_

 

 

 

(Leuc
and 5
1998)
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1981).

(Leucanthemum xsuperbum Bergman ex. J. Ingram ‘Snowcap’) decreased 80% , 75%,
and 55% , respectively, as temperature increased from 16 °C to 26 °C (Yuan et al.,
1998). In a study on campanula (Campanula carpatica Jacq. ‘Blue Clips’), the number
of ﬂower buds decreased linearly, at -10 ﬂowers per °C as plant temperature increased
from 16 to 24 °C (under ambient CO2 concentration) (Niu et al., 2001).
Flower Size

In general, mature ﬂower size decreases as the temperature at which plants are
grown increases. Lee et al. (1990) demonstrated that impatiens grown at a high
temperature regimen (35 °C DT / 30 °C NT) for four weeks had smaller ﬂowers
compared to those grown at a low temperature regimen (24 °C DT/18 °C NT), and that
the relative decrease in size differed among cultivars. Cultivars had 13 to 33% larger
ﬂowers at the cooler temperatures.

Similar results were observed with pansy ‘Universal Violet’; ﬂower size,
determined 4 days after anthesis, decreased linearly from z25 cm2 to z5 cm2 as
temperature increased from 9 °C to 31 °C (Pearson et al., 1995). Additionally,
temperature delivered from visible bud to ﬂowering had the most inﬂuence on ﬁnal
ﬂower size, and longer durations of higher temperatures led to progressively smaller
ﬂowers (Pearson et al. , 1995). Geranium ‘Sooner Red’ ﬂower diameter had a
quadratic relationship with temperature (Table 1); ﬂower size was greatest (~48 cm) at
15 °C and decreased (to ~28 cm) as temperature increased to 32 °C (Armitage et al.,

1981).

14

 

 

 

 

based 0
2001).

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Temper

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35 “c,
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2000).
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Campanula ‘Blue Clips’ and ‘Birch Hybrid’ showed differences in ﬂower size
based on the temperature treatment during speciﬁc times of development (Niu et al. ,
2001). Flower size was negatively correlated with ADT after visible bud; ﬂowers on
plants grown at 14 °C were 35 % larger than those on plants grown at 26 °C.
Temperature before visible bud had only a small effect on ﬁnal ﬂower size in both
species (Niu etal., 2001).

When grown under supplemental lighting at a range of temperatures from 15 to
35 °C, vinca ﬂower diameter was greatest (254.3 cm) at 25 °C (Pietsch et al. , 1995). At
35 °C, ﬂower diameter decreased to z3.8 cm (Pietsch et al., 1995). Similarly, Cosmos
[Cosmos atrosanguineus (Hook) Voss] ﬂower area decreased linearly from z17.5 cm2
to z7.5 cm2 as temperature increased from 13 °C to 26 °C (Kanellos and Pearson,
2000). In a separate study, as temperature increased from 16 to 26 °C, ﬂower diameter
decreased by 2.7 cm (z33 %) in Leucanthemum and Rudbeckia and by 0.9 cm (zl 6%)
in Coreopsis (Yuan et al., 1998).
Plant Mass

Plant mass is used as a measure of the overall size and vigor of the plant. In
impatiens, plant canopy size (average of plant width and height) and shoot dry weight
generally increased as temperature increased from 24/18 °C DT/NT to 35/30 °C DT/NT
after 4 weeks, showing a thermal time difference (Lee et al. , 1990). For example,
‘Accent Red’ plant size increased from 20.3 to 26.6 cm, and shoot dry weight increased

from 3.95 to 4.42 g as temperature increased (Lee et al. , 1990).

15

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Plant Height

Producing compact plants is desirable for shipping and general aesthetic value;
temperature and the difference between DT and NT (DIF) can affect plant height. In
many species such as Lilium longiﬂorum Thunb., Campanula isophylla Moretti. ,
Fuchsia xhybrida Hort. ex Vilm. , and Dendranthema grandiﬂorum Ramat.(Kitamura),
a higher NT than DT results in shorter internodes compared to when NT< DT (Erwin
and Heins, 1995).

Geranium ‘Red Elite’ and ‘Cardinal Orbit’ grown at a 7 °C NT were more
compact and were z50% shorter than those at an 18 °C NT when measurements were
recorded after 67 days, but ﬂowering was delayed by 3 weeks (Merritt and Kohl,
1989). In a separate study, geranium ‘Encounter Red’ was 1 to 2 cm shorter at
ﬂowering with a NT of 13 °C compared tol7 °C NT, under different light regimens
(Tsujita, 1981). However, results of both studies are confounded with the
developmental stage in which height measurements are taken. Measurements taken at
the same time during the experiment show differences due to thermal time, but the
plants may be at different developmental stages (i.e. , some may be vegetative under
cooler temperatures while those grown warmer may be reproductive).

Cosmos plant height at ﬁrst ﬂower doubled as temperature increased from 13 °C
to 26 °C (Kanellos and Pearson, 2000). In contrast, height of Rudbeckia at ﬁrst
ﬂowering decreased by 50% (from 248 cm to z24 cm) as temperature increased from

16 to 26 °C (Yuan et al., 1998). Plant height of Leucanthemum also decreased by z15

16

 

 

 

cm (.
Leucc

DIF.

tempc
rangii
DLI (

hi ghe
were '
nature
PTOmt

Light

in the

cm (27%) with increasing temperature (Yuan et al. , 1998). In the study of
Leucanthemum and Rudbeckia, the decrease in height may have been inﬂuenced by
DIF.

Campanula carpatica ‘Blue Clips’ plant height was not affected by average daily
temperature, but increased linearly as DIF increased from -6 to 12 °C under DLIs
ranging from 4.2 to 15.8 mol-m'Z-d", with the strongest response being under the low
DLI (Niu et al., 2001). However, this response may have been partially affected by the
higher red to far red ratio under the high light treatments in this experiment; HPS lights
were used in the higher light treatments and have a greater red to far red ratio than
natural sunlight. Red light has been shown to reduce elongation whereas far red light
promotes stem elongation (N iu et al. , 2001).

Light Integral Effects on Growth and Development

Daily light integral varies by latitude and by time of year. Outdoor mean DLI
in the US. ranges from 5 to 10 mol-m'z-d“ across the Northern US. in December to 55
to 60 mol-m'z-d'l in the Southwestern US in May through July (Korczynski et al.,
2002). The primary DLI differences from May through August between the eastern and
western US. are due to regional weather patterns, and to some extent, elevation. From
October through February, differences between the northern and southern US. are due
more to differences in solar duration and quantum ﬂuxes (Korczynski et al. , 2002).
The most rapid changes in DLI occur during the months surrounding the vernal and

autumnal equinoxes (Korczynski et al., 2002).

17

 

 

 

solar
obst
Lane
(Fﬁu
trans
greet
year.
‘Tila

(hﬁu

—o N w 0 0| 0,
O c: D a A A

Dally Ugh! Integral (nml tn"d")

O

Rate c

of gr€e

and no.

The amount of light plants receive in a greenhouse is affected by the amount of
solar radiation and also the interference from greenhouse glazing, structures, and other
obstructions. For example, natural light levels outdoors in midsummer in East
Lansing, Michigan average about 45 mol-m'z-d", and in midwinter about 10 mol-m'z-d'1
(Niu et al., 2001). Due to glazing and structures, and shading during the summer, light
transmission is often reduced by about 65 to 75%. So, a typical glass-glazed
greenhouse in Michigan will transmit an average of about 6 to 25 mol-m’Z-d‘l during the
year. Figure 2 illustrates and example of the differences between DLI observed at 43
°N latitude and at 33 °N latitude, and also differences inside and outside of a greenhouse

(Niu et al., 2001).

 

 

—I-- Outdoors ..
new In guesthouse without shack
«a..- In greenhouse with shade

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Daily Light Integral (mol m‘2d")

Figure 2. Average daily light integral in East Lansing, MI (43 °N latitude) and
Phoenix, AZ (33 0N latitude) outside and inside a typical greenhouse (N iu et al.,
2001).

Rate of Flower Development and DLI
A positive effect of high irradiance on ﬂowering has been reported for a number

of greenhouse crops, but the importance of supplementary lighting for ﬂoral evocation

and ﬂower development seems to differ considerably among species (Moe, 1997). The

18

T

 

 

 

rate of

develo

extens:
Craig :
inﬂuer
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Obserw
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rate of ﬂoral development partly depends on available photosynthates, so ﬂoral
development can be inhibited or delayed under low light intensities.

The effects of supplemental light on the rate of development have been studied
extensively on geranium (Pelargonium xhortorum L.H. Bailey). A study performed by
Craig and Walker (1963) conﬁrmed that the ﬂowering of seedling geraniums was
inﬂuenced by cumulative solar energy, and not simply the number of days from
transplanting to ﬂowering. Non-pinched plants grown at the same temperatures (13 °C
NT/ 18 °C minimum DT) at different times of the year, hence different light intensities,
had different number of days to ﬂower, but required similar amounts of cumulative
solar energy to ﬂower [z55,000 g-cal/cm2 (outdoor)].

More recent studies have provided similar results. Erickson et al. (1980)
observed in geranium ‘Sprinter Scarlet,’ ‘Sprinter White’, and ‘Ringo’ that average
daily cumulative energy levels inﬂuence ﬂowering. Forty-one to 65 % of the variability
in days to ﬂower was associated with cumulative solar energy, which is confounded
with temperature. This study also indicated that days to ﬂower may decrease with
increasing light intensity at low light levels until a threshold level (z7 mol-m‘Z-d“) is
reached.

In a separate study by Armitage and Tsujita (1979), four seed propagated
cultivars of geranium (‘Sprinter Scarlet’, ‘Carefree Crimson’, ‘Carefree Bright Pink’,
and ‘Carefree Dark Salmon’) were studied to determine the effect of supplemental light
source and quaan ﬂux density on ﬂowering. Plants were grown under 32 or 64

umol-m'Z-s‘l from high pressure sodium (HPS) lamps and 27 or 54 umol-m‘Z-s‘I from low

19

 

 

 

press
seed

com;

ﬂow:
week
6 wet
from

Chin]:

d0 DO]
and 2;
I0 Visi
aDOVQ

aCCelei

pressure sodium (LPS) lamps for 2, 4, or 6 weeks. Regardless of cultivar, days from
seed to ﬂowering were reduced by at least 11 days under 6 weeks of HPS lighting
compared with ambient light alone, but there was no reduction under LPS lighting.

The promotion of supplemental lighting varied by cultivar; ‘Carefee Bright Pink’
ﬂowered earlier with six weeks of low intensity HPS lighting and with 2, 4, and 6
weeks of high intensity light while ‘Carefree Deep Salmon’ only ﬂowered earlier under
6 weeks of high intensity HPS lighting. Cumulative supplemental quanta (mol-m'z)
from HPS was negatively correlated with days to ﬂower of ‘Sprinter Scarlet’, ‘Carefree
Crirnson’, and ‘Carefree Deep Salmon’.

Although some geranium cultivars ﬂower earlier with an increase in DLI, others
do not. For example, ‘Red Elite’ seed geraniums under DLI treatments of 15.1, 19.8
and 24.6 mol-m‘Z-s'l from sixth leaf stage to visible bud, showed no differences in time
to visible bud (White and Warrington, 1984). However, 15 mol-m'z-s" may have been
above a threshold DLI, which could explain why further increases in DLI may not have
accelerated ﬂowering.

Geranium ‘Sooner Red’ grown under ambient light initiated ﬂowers 37 days
earlier and differentiation time was reduced by 7 days compared to plants grown under
60% shade (Armitage and Wetzstein, 1984). Shade—grown plants had 22-24 nodes at
ﬂower initiation compared with 1618 under ambient light (Armitage and Wetzstein,
1984). There was a 1-2 °C difference in plant temperature on a clear day between the
shaded and ambient part of the greenhouse bench, so the delays observed under the

shade may have been affected by slightly lower temperatures. Higher light intensities

20

T

 

 

 

decrea

well as

incana
HPS lig
ambient
‘Pizzazz

:14 day.

 

decreased the juvenile period by decreasing time from sowing to ﬂower initiation as
well as time for ﬂoral organ differentiation (Armitage and Wetzstein, 1984).

Beneﬁts of supplemental lighting have also been observed in stock (Matthiola
incana L.). At 18 °C DT/14 °C NT, plants under an additional 60 umol-m'z-s'l from
HPS lighting (l6-h day) ﬂowered 20-25 days earlier compared with plants under
ambient light conditions (Dansereau et al., 1998). Begonia semperﬂorens plugs
‘Pizzazz Red’, ‘Vodka’, and ‘Viva’ days from sowing to visible bud were reduced by
z14 days, zl9 days, and 2:15 days for each cultivar, respectively, when exposed to 125
umolom'Z-s'l supplemental metal halide light in comparison with treatments of 50 and
200 umol-m‘z-s‘l (at 18 °C NT and a DT that did not exceed 29 °C) (Kessler et al.,
1990). There were no signiﬁcant differences between 50 and 200 umol-m‘z-s'l (Kessler
et al., '1990). This may indicate a threshold light level for Begonia, which is often
considered a shade tolerant plant. In petunia, a DLI of 13 rather than 6.6 mol-m'z-d'l
decreased time to ﬂower by up to 3 weeks (Kaczperski et al., 1991). However in
campanula ‘Blue Clips’, increasing DLI from 4.2 to 15.8 mol-m’z-d'l did not have an
effect on time to ﬂower when grown at temperatures ranging from 15 to 25 °C (Niu et
al., 2001).

Plant Quality and DLI

Plant quality is greatly affected by the total amount of irradiance a plant
receives. In general, the greater the DLI, the higher quality the plant. Some measures
of quality affected by DLI are plant height, branching, dry weight, ﬂower size and

ﬂower number.

21

Plant Height

Plant height can also be affected by DLI, often with increases in DLI leading to
decreases in height. In geranium ‘Sprinter Scarlet’, ‘Sprinter White’, and ‘Ringo’, total
and vegetative plant height were correlated to DLI (Erickson et al., 1980). Signiﬁcant
differences in vegetative and total height were observed between 4, 6, 9, 10, and 12
mol-m""-d‘l for each cultivar; as DLI increased, height decreased (Erickson et al., 1980).
Branching

In geranium ‘Sprinter Scarlet’, ‘Sprinter White’, and ‘Ringo’, the number of
lateral breaks increased from zl to z4 as cumulative PAR increased from 4 to 12
molom‘Z-d‘l (Erickson et al., 1980). In Begonia ‘Rosalie’ and ‘Schwabenland’, the
number of side shoots per plant was greater (by 2.5 and 2, respectively) with
supplemental HPS lighting (z32 ttmol-m'Z-s’1 additional for 16-h) compared to plants
grown under ambient light alone (Vogelzang and Veberkt, 1990). However, these
signiﬁcant differences were only observed when plants were grown in November (when
ambient light levels were lower) as opposed to those grown beginning in February
(V ogelzang and Veberkt, 1990).
Dry Weight

For ornamental plants, the most useful measure of the efﬁciency of higher plant
growth is grams of total biomass per mol of photosynthetic photons (Moe, 1997). In
general, as DLI increases, dry weight increases, although the rate of dry weight

increases at a decreasing rate.

22

DLI had a positive linear effect on increasing seedling dry weight accumulation
43 days post emergence in Petunia xhybrida ‘Red Flash’; there was a 10% increase in
dry weight between plants sown in February to those grown in March, hence under
higher light intensities later in the spring. (Graper et al. , 1990). In a separate study,
Graper and Healy (1992) investigated Petunia xhybrida ‘Red Flash’ seedlings and
found that doubling DLI from 10 to 20 mol-m’z-d'l increased total carbohydrate
production by 60% , seedling dry weight by 30% , and rate of seedling growth by 25%.

There was over a 50% increase in Begonia semperﬂorens Link & Otto. ‘Pizzazz
Red’, ‘Vodka’, and ‘Viva’ seedling dry weight after 8 weeks under a supplemental
lighting treatment of 125 umol-m‘z-s" provided by metal halide lamps, compared with
plants under 0, 50, or 200 umol-m'Z-s'l (16-h days) (Kessler et al., 1990). In a study on
foliage plants, supplemental HPS lighting (:44 umol-m'z-s'1 for a 16-h day) increased
dry weight by 146% in Hedera sp. L. ‘Variegata’, 82% in Fatshedera sp. Guill. ‘Pia’,
93% in Codiaeum sp. A. Juss. ‘Gold Sun’, and 100% in Ficus sp. L. ‘Starlight’, when
grown at 22 °C DT/ 20 °C NT as compared with ambient light levels (V ogelezang and
Verberkt, 1990).
Flower Size and Number

Flower size and number generally increase as DLI increases. Flowers of shade
grown geranium ‘Sooner Red’ were smaller and fewer in number, compared with
ambient grown plants, both during differentiation and at anthesis (Armitage and
Wetzstein, 1984). In Campanula ‘Deep Blue Clips’, ﬂower size and number were

similar when grown under DLIs ranging from 5 to 17 mol~m""-d‘1 before visible bud

23

 

 

 

ﬂoue
plants
across
Intera

Floral

TCmpe]
‘Fhefﬁ
“muﬁc
ianMU
temperai
‘Fhth
days:res
acﬁelermc

ThCre WC]

Ilghtlng CC

(Niu et al., 2001). Supplemental lighting after visible bud partially compensated for
smaller ﬂower number under higher temperatures; the number of ﬂower buds was
240% higher under 17 mol-m'Z-d'1 after visible bud at 22 to 24 °C than under 5 .7 mol-m‘
2-cl‘l at 14 to 16 0C (Niu et al., 2001). Flower size also increased as DLI increased; at
temperatures ranging from 14 to 26 °C, ﬂowers were z10-15% larger under 17 mol-m‘
z-d‘l than under 5 mol-m‘z-d'l (Niu et al., 2001). In vinca ‘Grape Cooler’ increased
ﬂower size (15—20%) was observed under a DLI of z29 mol-m‘z-d" in comparison with
plants under ambient (z18 mol-m’Z-d") and under 50% shade cloth (z9 mol-m”2-d“)
across temperatures ranging from 15 to 35 °C (Pietsch et al., 1995).
Interaction of Temperature and Light Intensity
Floral Development Rate

Rate of ﬂower development can be affected by temperature and light intensity.
Temperatures of 13 °C versus 17 °C delayed ﬂowering by two weeks with Geranium
‘Fire Flash’, ‘Encounter Red’ and ‘Sprinter Salmon’ (Tsujita, 1982). Although no
statistical interaction between light and temperature was found, supplementary HPS
irradiation for 6 or 8 weeks overcame the delay in ﬂowering induced by low night
temperature. Six or eight weeks of supplemental HPS lighting accelerated ﬂowering of
‘Fire Flash’ by 8 or 13 days, respectively, at 17 °C and ‘Sprinter Salmon’ by 14 or 17
days, respectively, at 17 °C (Tsujita, 1982). Four weeks of supplemental HPS lighting
accelerated ﬂowering of ‘Encounter Red’, by approximately 11 days (Tsujita, 1982).
There were no plant temperatures reported in this study, so the 6 or 8 weeks of the HPS

lighting could have increased plant temperature, and thus partially explain the earlier

24

 

 

00
ten
rec
1.7
Ho‘
[CH1

1(64

undc
ﬂow
aver

lime

and 1

him

ﬂowering. Studies on vinca (Catharanthus roseus L.) showed that shoot tip
temperature can be greater than air temperature (Faust and Heins, 1997). Shoots

. receiving supplemental HPS lighting of 50, 75, and 100 pmolom'z-s’l were 1.2, 1.5, and
1.7 °C higher, respectively, than that of plants in the dark (Faust and Heins, 1997).
However, in a similar study, no statistically signiﬁcant interactions between
temperature and light intensity were reﬂected in growth and development of geranium
‘Red Elite’ when leaf temperatures were used (White and Warrington, 1984).

In petunia ‘Snow Cloud’, plants ﬂowered in 67 days when grown at 20 °C and
under 6.5 mol-m'Z-d“; however, when the light intensity was doubled, the plants
ﬂowered in 56 days (Kaczperski et al., 1991). In this study, it was shown that the
average temperature could be lowered to 15 °C and plants would still ﬂower at the same
time as those grown at 20 °C at the lower irradiance (Kaczperski et al. , 1991).

Different phases of development may be inﬂuenced differently by temperature
and light intensity. In 1999, Adams et al. studied the effects of temperature and light
intensity on the different phases of photoperiod sensitivity in petunia ‘Express Blush
Pink.’ They showed that the length of the photoperiodninsensitive juvenile phase of
development was sensitive to light integral and temperature. Low light integrals
prolonged the phase from 23 days under 5.1 mol-m'z-d" to 36 days under 3.1 mol-m'z-d'
'. The length of this phase was shortest (13 days) at 21 °C, and longer at 13.5 °C and
28 0C (21 and 18 days, respectively). After this phase, time to ﬂowering was primarily
inﬂuenced by photoperiod, with long days (16-h) hastening ﬂowering between 28 and

137 days, as compared with short days depending on the temperature. The duration of

25

the ﬁnal phase of development was dependent primarily on temperature; at 14.5 °C, it
took 34 days to complete this phase and at 25.5 °C it took 11 days.

Another example of different inﬂuences of temperature and light intensity
during different developmental phases occurred with geranium ‘Sooner Red’. Time
from seed to visible bud was negatively correlated to quantum ﬂux density at a given
temperature; however, the time from visible bud to ﬂowering was negatively correlated
with temperature, while light had no effect (Armitage et al. , 1981).

In 1997, a study on the quantitative long day plant pansy ‘Universal Violet’ by
Adams et al. showed that temperature, DLI, and photoperiod each had independent
linear effects on the rate of progress to ﬂowering, without any interaction.
Interestingly, the estimated optimum temperature for time to ﬂower decreased linearly
from z21 °C to z16 °C as DLI decreased from z6.7 mol-m'z-d‘l to ~4 mol-m’Z-d".
Height and Shoot number

Plant height at ﬂowering of petunia ‘Snow Cloud’ increased as day temperature
increased from 10 °C to 30 °C (Kaczperski et al., 1991). Plant height was inﬂuenced
more by low irradiance (6.5 mol-m‘z'd") at warmer temperatures than cooler
temperatures; plants were 20% shorter at 30 °C and only 4% shorter at 10 °C under 6.5
mol-m'zd'l as compared to those grown under 13 mol-m'z-d'l (Kaczperski et al., 1991).

Temperature signiﬁcantly affected plant height at ﬂowering of geranium
‘Encounter Red’ under all light treatments. Plants grown at 13 °C NT were shorter (7-

10%) and had a larger number of shoots (20-130%) than plants grown with a 17 °C NT

26

 

 

 

(Tsuj

14%

gain 5

(Tsujita, 1982). ‘Sprinter Salmon’ and ‘Fire Flash’ lighted for 8 weeks were 10 and
14% shorter, respectively, at 13 °C than at 17 °C (Tsujita, 1982).

In Impatiens ‘Accent Red’, linear regression coefﬁcients of shoot height as a
function of plug medium temperature were 67 to 172% higher for seedlings grown
under 24-h continuous lighting of z215 umol-m'Z-s‘l as compared with those grown
under z335 umol-m‘z-d‘l in a growth chamber (Dressen and Langhans, 1992). The
predicted height of seedlings grown at a lower light level at a plug medium temperature
of 20, 22.5, and 25 °C are 2%, 7%, and 18% greater, respectively, than those for high
light seedlings at the same temperature (Dressen and Langhans, 1992).

Plant mass

Plant mass can be affected by both temperature and light. One model developed
for petunia ‘Snow Cloud’, indicated that the optimum temperature for shoot dry weight
gain shifts from 14.6 °C at 5 mol-m‘z-d‘l to 33.5 °C at 30 mol-m'z-d"(Lieth et al.,1990).
A separate study on pansy ‘Universal Violet’ indicated that dry matter accumulation
was primarily a function of temperature and DLI (Adams et al., 1997). Shoot dry
weight was greatest at temperatures of z20 °C and dry matter accumulation was reduced
at both warmer and cooler temperatures. Additionally, relative growth rate increased
linearly with DLIs up to z20 mol-m’Z-d'l (Adams et al. , 1997). This model presented
for pansy ‘Universal Violet’ did not predict an optimum temperature shift with changes
in DLI, but the authors suggest that this may be a potential deﬁciency in the model and

may account for some unexplained variance (Adams et al., 1997).

27

 

seedlir
pl'OdUt
irradia
20 day
1990).
Supple
120 pr.
develo

Ambie

167 lift
for 14 (
Weight)
fOr Up [I

[Manuel

3130 bee

366mm,

Some studies have been performed on the effects of temperature and DLI on
seedling dry weight, as this is an important factor of growth and quality in plug
production. In Petunia xhybn'da ‘Red Flash’, the critical period for supplemental
irradiation to obtain an optimum increase in seedling dry weight was 10-15 days or 10-
20 days after germination with supplemental root zone heating to 27 °C (Graper et al.,
1990). Providing light before or after this period was 30% less effective.

Supplemental root zone heating to 27 °C combined with additional 24-h HPS lighting of
120 nmol-m‘zs’l increased rates of seedling development. Part of the increase in
development was due to increased soil temperature under higher light intensities.
Ambient soil temperatures ranged from 17.5 0C to 21.1 °C under the 13 to 233 umol-m‘
2~s‘l lighting treatments, up to a 4 °C difference (Graper et al. , 1990). Additionally,
indicate that as the spring season progressed from January to March and DLI increased.
subsequent time to ﬂower decreased by up to 14 days (Graper et al. , 1990).

In a separate study on Petunia xhybrida ‘Red Flash’ , providing an additional
167 umol-m'z-s'l from HPS lighting (24-h) and increasing plant temperature by 4.3 °C
for 14 days following seedling emergence increased relative growth rate (based on fresh
weight) by 45% (Graper and Healy, 1991). The increased growth rate was observed
for up to seven days after treatment, but was not sustained after removal from the
treatment (Graper and Healy, 1991).

A synergistic effect between supplemental irradiance and root zone heating has
also been reported for Begonia sempetﬂorens ‘Vodka’ (Graper and Healy, 1990).

Seedling dry weight accumulation, 43 days post emergence, increased (linearly and

28

T

quadratically) with increasing supplemental HPS irradiance (ranging from 13 to 233
umol-m’z-s’l for 24-h) provided 15 through 25 days after emergence (Graper and Healy,
1990). At ambient soil temperatures, seedling dry weight increased by 25% as
supplemental irradiance increased from 13 to 233 umol-m’Z-s". The addition of root
zone heating to the increase in irradiance increased dry weight by 33% (Graper and
Healy, 1990). As an additional beneﬁt, as the initial supplemental light increased from
13 to 233 umol-m'Z-s" (applied days 15-25 post emergence), days to transplant and days
to ﬂower decreased by :5 days (Graper and Healy, 1990). This decrease in days to
ﬂower may have been partially inﬂuenced by increased temperature under higher light
intensities, but plant temperature was not reported.

Impatiens ‘Accent Red’ (10 to 25 days old) were also studied to determine the
effects of 24-h supplemental lighting (z215 to 2:335 pmol-m’Z-s") and temperature (18-
29 °C) on seedling dry weight in growth chambers (Dressen and Langhans, 1992).
Shoot dry weight was linearly related to plug medium temperature at all irradiance
levels studied, except for those under the highest light intensity (z335 umol-m’z-s"). At
high irradiance levels, shoot dry weight decreased at plug medium temperatures >25
°C. At lower light levels, shoot dry weight continued to increase with all temperatures
studied (Dressen and Langhans, 1992). The maximum relative growth rate was
predicted to occur 12 days from sowing at 19.6 °C, 11 days at 21.6 °C, and 10 days at
23.6 °C. Cooler temperatures delayed the occurrence of the highest relative growth

rates (Dressen and Langhans, 1992).

29

 

Leaf

has r
Afric
unfol
(Fans
decree
decrea
unfold
Violet'

Photot.

energy .
(L111 an(
t“ C) abo
Per Plan
reProduc

(Llu and

dry Weig}
ICached a

Leaf Unfolding Rate

The combined effect of DLI and temperature on vegetative development rates
has not been determined on the vast majority of herbaceous plants. One example with
African violet (Saintpaulia ionantha Wendl. ‘Utah’) showed that maximum leaf
unfolding rate was 0.27 leaves-d“, which occurred at 25 °C and with 10 mol-m‘zod'l
(Faust and Heins, 1993). However, the optimum air temperature for leaf unfolding
decreased to 23 °C and the maximum rate decreased to 0.18 leaves-d"a s the DLI
decreased from 10 to 1 mol-m'Z-d‘l (Faust and Heins, 1993). In a separate study, leaf-
unfolding rate was linearly related to mean temperature and DLI in pansy ‘Universal
Violet’ (Table 1) (Adams et al., 1997).
Photothermal ratio

Recently, the concept of combining the effects of thermal energy and radiant
energy into a photothermal ratio (PTR).has been investigated in poinsettia ‘Freedom’
(Liu and Heins, 2002). PTR is a ratio of mean DLI (mol'm'z-d") to mean temperature
(°C) above a base temperature, and the units for this measurement are mol/degree-day
per plant. The effects of PT R during the vegetative stage (PT R”) and during the
reproductive stage (PT R') on plant quality in poinsettia ‘Freedom’ were investigated
(Liu and Heins, 2002).

Both PT Rr and PT R" affected ﬁnal plant dry weight. Total, leaf, stem, and bract
dry weight increased linearly as PT Rr increased and responded quadratically and
reached a maximum when PTRv was 0.04 mol/degree—day per plant. When PT R"

increased from 0.02 to 0.06 mol/degree day per plant, stem diameter increased by

30

 

linear
diam:
PT Rr

demo:
demor

grout.

correlz
et al. _

increag
mOI/de

abOVe :

z24%, while stem strength increased 75%. The size of bracts and cyathia increased
linearly as PTRr increased, but was unaffected by PTR". Bract area, inﬂorescence
diameter, and cyathia diameter increased 45%, 23%, and 44%, respectively, when
PTR' increased from 0.02 to 0.06 mol/degree-day per plant. This experiment not only
demonstrates the combined effects of thermal and light energy on plant quality, but also
demonstrates that the effects differ between stages of vegetative and reproductive
growth and development.

In Campanula carpatica ‘Blue Clips,’ ﬂower bud number and dry mass were
correlated closely to PTR, while ﬂower size was only weakly correlated with PTR (Niu
et al., 2001). Flower bud number increased (from ~25 to z200) and dry mass
increased (from zl to z6 g/plant) linearly as PTR increased from 0.2 to 1.0
mol/degree-day. However, ﬂower size was more closely related to temperature; DLIs

above 10 mol-m'Z-d" did not increase ﬂower size.

31

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33

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Lee, W.S., J .E. Barrett, and TA. Nell. 1990. High temperature effects on the growth
and ﬂowering of Impatiens wallerana cultivars. Acta Hortic. 272:121-127.

Lieth, J.H., R.H. Merritt, and HG Kohl, Jr. 1991. Crop productivity of petunia in
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Sci. 116(4):623-626.

Lin, B., and RD. Heins. 2002. Photothermal ratio affects plant quality in ‘Freedom’
poinsettia. J. Amer. Soc. Hort. Sci. 127(1):20-26.

Michigan Department of Agriculture (MDA). 2001. Michigan Agricultural Statistics
2000-2001, Horticulture. Lansing, MI.

Merritt, RH. and HG Kohl, Jr. 1989. Crop productivity and morphology of petunia
and geranium in response to low night temperature. J. Amer. Soc. Hort. Sci.
114(1):44-48.

Moe, R. 1997. Physiological aspects of supplementary lighting in horticulture. Acta
Hortic. 418:17-23.

34

Moe, R. and R. Heins. 1990. Control of plant morphogenesis and ﬂowering by light
quality and temperature. Acta Hortic. 272:81-89.

Niu, G., R.D. Heins, A.C. Cameron, and W.H. Carlson. 2001a. Temperature and
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36(4):664-668.

Niu, G., R.D. Heins, A.C. Cameron, and W.H. Carlson. 2001b. Day and night
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Pietsch, G.M., W.H. Carlson, R.D. Heins, and J .E. Faust. 1995. The effect of day
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Salisbury, RB. and C .W. Ross. 1992. Plant Physiology, 4‘h ed. Growth responses to
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35

Yeh, D.M., J .G. Atherton, and J. Craigon. 1999. A thermal time model of post-
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340.

Yuan, M., W.H. Carlson, R.D. Heins, and A.C. Cameron. 1998. Effect of forcing

temperature on Coreopsis grandiﬂora, Gaillardia xgrandiﬂora, Leucanthemum
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36

SECTION II

The Effects of Temperature and Daily Light Integral on Bedding Plant Plug Growth and

Development

37

The Effects of Temperature and Daily Light Integral on Bedding Plant Plug
Growth and Development

Lee Ann Pramukl and Erik S. Runkle"

Department of Horticulture, Michigan State University, East Lansing, MI 48824

Additional index words: Celosia, Impatiens, Saliva, T agetes

Received for publication . Accepted for publication . We

 

 

gratefully acknowledge funding from growers providing support for Michigan State
University ﬂoriculture research and support from the Michigan Agriculture Experiment
Station.

1 Graduate Student. Current address: Michigan State University, Dept. of Horticulture,
East Lansing, MI 48824

2 Assistant Professor of Horticulture and Extension Specialist, to whom reprint requests

should be addressed (Email: runkleer@msu.edu).

 

38

Introduction

The production of bedding plants in northern climates forces bedding plant plug
growers to rely on heating in the winter and early spring. Additionally, some growers
use supplemental lighting because of naturally low light levels. In response to
increasing energy costs, growers may change temperature set points or lighting
strategies to reduce short-term fuel costs, but crop timing and quality may be
compromised in the process. Crop timing during the plug stage is of great importance
due to speciﬁc market dates. Quality factors, such as compactness and strong, thick
stems are important during shipping and for ease of transplant.

Temperature and daily light integral (DLI) are known to affect plant growth and
development, and studies on this interaction have been performed in some species such
as petunia (Petunia xhybrida Hort. Vilm.-Andr.), pansy (Viola xwittrockiana Gams.),
vinca (Catharanthus roseus L.), and geranium (Pelargonium xhortorum Bailey) (Adams
et al., 1997; 1999; Armitage et al., 1981; Pietsch et al., 1995). However, these studies
mainly focus on the ﬁnish stages of plant and ﬂower development. With the advent of
plug technology comes a need to understand how these factors affect plant growth and
development speciﬁcally during the seedling stage.

Some studies have been performed on seedlings to determine the relationship
between dry weight, a main indicator of growth and quality in plugs, and the interaction
between temperature and supplemental lighting. In Begonia semperﬂorens seedlings,

supplemental irradiance and root zone heating had a synergistic effect in dry weight

39

accumulation (Graper and Healy, 1990). At ambient soil temperature, seedling dry
weight increased by 25% as the irradiance increased from 13 to 233 umol-m’Z-s". The
addition of root zone heating and the increase in irradiance increased dry weight by
33% (Graper and Healy, 1990). In Petunia xhybrida, supplemental root zone heating
to 27 °C combined with additional 24-h HPS lighting of 120 pmol-m‘z-s‘l increased rates
of seedling development (Graper et al., 1990). However, part of the increase in
development was due to increased soil temperature under the higher light intensities;
the difference between plants under the 13 to 233 umol-m'z-s'l lighting treatments varied
by up to 4 °C (Graper et al. , 1990). In a separate study on Petunia xhybrida, providing
an additional 167 umol-m‘Z-s'l HPS lighting (24-h) and increasing plant temperature by
4.3 °C for 14 days following emergence increased seedling relative growth rate (based
on fresh weight) by 45% (Graper and Healy, 1991). Seedling shoot dry weight of
Impatiens ‘Accent Red’ (10 to 25-day old) was linearly related to plug medium
temperature (18-29 °C) under all irradiance levels (#215 to z335 umol-m'z-s"), except
for those under the highest light intensity (Dressen and Langhans, 1992). At high
irradiance levels, shoot dry weight decreased when plug medium temperature was
greater than 25 °C.

Although these studies provide information on the interaction of temperature and
light on some species during the seedling stage, more research in this area is warranted
due to the variability of optimum temperatures and light requirements among species

and between growth and developmental processes.

40

This research was designed to determine how temperature and DLI inﬂuence
growth and quality of four popular bedding plant species at the seedling (plug) stage:
Celosia argentea var. plumosa ‘Gloria Mix’, Impatiens wallerana ‘Accent Red’, Salvia
splendens ‘Vista Red’, and T agetes patula ‘Bonanza Yellow’.

Materials and Methods

Seeds of T agetes patula ‘Bonanza Yellow’, Impatiens wallerana ‘Accent Red’,
Celosia argentea var. plumosa ‘Gloria Mix’, and Salvia splendens ‘Vista Red’ were
sown in 288-cell plug trays on 4 January 2002 and 2 April 2002 at a wholesale plug
producer (Raker’s Acres, Litchﬁeld, MI). Plants were received at Michigan State
University on 10 January 2002 and 8 April 2002. Plugs were placed on capillary mats
and were top irrigated with well water (containing 95, 34, and 29 mg-L'l Ca, Mg, and
S, respectively) supplemented with a water soluble fertilizer to provide the following
(mg-L"): 40 N, 4 P, 40 K, 5 Ca, 0.3 Fe, 0.03 B and Mo, and 0.2 Mn, Zn, Cu (MSU
Special; Greencare Fertilizers, Chicago, IL). The water was acidiﬁed with H280, to a
titratable alkalinity of z140 mg~L’l CaCO3.

The plug trays were split in half, thinned to one seedling per cell, and randomly
placed in treatments in 5 glass glazed greenhouse compartments set at constant 14, 17,
20, 23, and 26 °C. Greenhouse air temperature was measured by an aspirated
thermocouple and soil temperatures were measured by a thermocouple placed just under
the soil surface under ambient light treatments. Average air temperatures were used for
analysis. Within each compartment, two half trays were placed under one of three light

environments, ambient light plus 50% shade cloth (OLS 50; Ludvig Svensson,

41

Charlotte, NC), ambient light, and ambient plus supplemental high-pressure sodium
(HPS) lighting (z170 pmol-m'zs"). Plants in all treatments were exposed to a 16-h
photoperiod, from 700 HR to 2200 HR, using HPS lamps which delivered ~34, z75,
z170 umol-m‘Z-s under the ambient light plus 50% shade cloth, ambient light, and
ambient plus supplemental high-pressure sodium, respectively. Line quantum sensors
(Apogee Instruments, Inc. Logan, Utah) were placed under the three lighting treatments
in three of the ﬁve greenhouse compartments to measure photosynthetic photon ﬂux
(PPF). Instantaneous values were converted to DLIs, which were used for analysis.
Vapor pressure deﬁcit was maintained at z0.7 kPa by steam injection. A CRlO data
logger (Campbell Scientiﬁc, Logan, Utah) recorded the environmental data every 10
seconds and hourly averages were reported (Table 1 and 2).

Plant height, node number, and shoot dry weight were recorded when plugs in
each light and temperature treatment were considered ready for transplant. T agetes
plugs were considered ready for transplant when the second set of leaves reached 4.5
cm across; Celosia, when seedlings were at least at the fourth leaf stage and were 4.5
cm across; Salvia, when the second leaf pair was 3.5 cm across; and Impatiens, when
the sixth leaf was 1 mm in length. Ten plants per half tray were measured, totaling 20
plugs per treatment per replication. Data were not recorded from the outer 2 rows of
plants, as to decrease edge effects. Date of visible bud was recorded if present at time
of transplant.

Average temperature and DLI were calculated for each treatment and regression

analysis was performed using SAS (SAS Institute Inc., Cary, NC) response surface

42

regression (RSREG procedure). If the contribution of individual terms to the model
were not signiﬁcant, the terms were removed, and regression (REG procedure) was
used to determine the model coefﬁcients. Individual terms were included if P < 0.05.
Results

Celosia. Time to fuiish was signiﬁcantly affected by temperature and DLI.
Plugs ﬁnished the earliest (in 20 days) when grown at 28 0C and under 24 mol~m"°'-d‘l
(Fig. 1). Increasing DLI decreased time to ﬁnish linearly at all temperatures,
especially at the lower temperatures. At 14 oC and under a DLI ranging from 4 to 17
molom'Z-d“, Celosia showed severe chlorosis and did not reach the ﬁnish stage within 60
days, when the experiment ended, so data were not included in any of the models.
Predicted base temperature was 12.4 0C under 10 mol-m'Z-d". Dry weight increased
linearly at all temperatures as DLI increased and was quadratically related to
temperature at all DLIs, reaching a maximum at 23 °C under 24 mol-m’z-d" (Fig. 2).
Seedling height was signiﬁcantly affected by temperature and DLI, but data were highly
variable (R2 =0. 17) (Fig. 3). Under 4 mol'm‘Z-d", plant height increased with
temperature. At the lowest temperatures studied (16 °C), plant height increased with
DLI. Node number increased from 6 to 12 as temperature decreased from 27 °C to 16
°C and DLI increased from 4 to 24 mol-m‘Z-d‘l (Fig. 4). The greatest percentage of
visible ﬂower bud (70%) at the time of ﬁnish was observed at 17 °C and under 16
mol-m'Z-d", while no buds were present when plugs were grown at 24 to 28 °C under all

light intensities (Fig. 5).

43

Impatiens. Time to ﬁnish was signiﬁcantly affected by temperature and DLI.
Fastest time to ﬁnish was 28 days at 27 °C and under 23 mol-m’Z-d", and was 35 days
earlier than plugs grown at 14 °C receiving 4 mol-m‘Z-d". Fig. 6 is the response surface
developed from the observed data. Predicted base temperature was 7.3 °C under 10
mol-m‘Z-d“. Impatiens dry weight was greatest at 14 °C and under 26 mol-m‘z-d‘l (Fig.
7). Impatiens had the least biomass and were tallest at the highest temperature and
lowest DLI (26 °C and 4 mol-mid") (Fig. 7 and 8). Plugs averaged between 5 to 8
leaves at ﬁnish (Fig. 9). Impatiens had high percentages of visible ﬂower bud when
grown under most temperature and DLI treatments; only those grown at 227 °C did not
have ﬂower buds at the time of ﬁnish (Fig. 10). -

Salvia. Time to ﬁnished plug was signiﬁcantly affected by temperature, but not
by DLI. Time to ﬁnish decreased by 20 days as temperature increased from 14 to 28
°C (Fig. 11). Predicted base temperature was 3 °C. Dry weight was signiﬁcantly
affected by both temperature and DLI, and was greatest at 14 °C under 24 mol-m’Z-d'l
and lowest at 26 °C and with 4 mol-m'z-d‘l of light (decreasing by z70%) (Fig. 12).
Plugs were tallest at 28 °C and 4 mol-mad" and were shortest under 14 °C and 4
mol-mad" (decreasing by z60%) (Fig. 13). At ﬁnish, all plugs under all treatments
had an average of 3 to 4 nodes (Fig. 14). Only plugs grown at 16 and 20 °C under the
highest DLI (2 19 mol-m‘Z-d") had visible ﬂower buds at the time of ﬁnish (Fig. 15).

Tagetes. Temperature had a signiﬁcant effect on days to ﬁnish, whereas DLI did
not. Days to ﬁnish decreased by z12 days as temperature increased from 14 to 28 0C

(Fig. 16). Predicted base temperature was -10.3 0C. Dry weight increased as DLI

increased at all temperatures, but DLI had the greatest effect at the coolest temperatures
(Fig. 17). Marigold height increased by 43% as temperature increased from 14 to 28
°C under 4 mol-m'Z-d‘l and by 15% under 26 mol-m‘z-d'l (Fig. 18). Plugs under all
treatments had 3 or 4 leaf pairs at ﬁnish (Fig. 19). Plugs had the lowest visible bud
percentage when grown warm (24 to 28 °C) and under the lowest DLIs (Fig. 20). At
least 60% were reproductive when grown at all other temperature and DLI
combinations.

Discussion

Temperature inﬂuenced days to ﬁnish in all species, while DLI had a signiﬁcant
effect on development time only in Celosia and Impatiens. Some of the effect
attributed to DLI may have been due to higher plant temperatures under the HPS
lamps. For example, it has been shown that the temperature of vinca shoots receiving
supplemental HPS lighting of 50, 75, and 100 umol'm'z-s'l was 1.2, 1.5, and 1.7 °C
higher, respectively, than that of plants in the dark (Faust and Heins, 1997).

Dry weight is an overall measure of the size and vigor of a plant. For plug
production, dry weight is important because strong plants are needed for transplanting,
especially with mechanized transplanting systems. Increasing DLI and temperature
have been found to increase dry weight of plugs in similar studies. Begonia
semperﬂorens dry weight (at 40 days post seedling emergence) increased as
supplemental irradiance increased from 13 to 233 umol-m’z-s'l (24-h), and was further
increased by root zone heating to 27 °C (Graper and Healy, 1990). In petunias,

increasing ambient light intensity by 53 % and elevating plant temperatures by 4.3 °C

45

increased seedling relative growth rate (In fresh weight) by 45 % (Graper and Healy,
1991). Our studies show similar results, as dry weight at ﬁnish was signiﬁcantly
affected by temperature and DLI in all species studied (Fig. 2, 7, ll, 15). The largest
increases in dry weight due to DLI were observed under the cooler air temperatures
where growth and development were slower. Thus, the plants had a longer duration of
time to harvest light. In Impatiens, dry weight generally increased with decreasing
temperature, although, when temperature was >20 °C, plant dry weight did not increase
as the DLI increased above as 14 mol m‘2 d". In Celosia, Salvia, and T agetes,
increasing daily light integral increased plant dry weight at all temperatures provided in
treatments. Additionally, growing Salvia, T agetes, and Impatiens under increasingly
cooler temperatures from 26 to 14 °C increased dry weight (and thus improved quality
and strength of the plugs). However, this strategy of increasing plug quality also
increases time to reach a mature plug.

Height is an important quality factor for plugs, as it is desirable to have compact
plugs for shipping, transplanting, and aesthetic purposes. At high DLIs as temperature
increased, height of T agetes, Salvia, and Impatiens increased, although height
decreased in Celosia. At low DLIs, height increased with increasing temperatures in the
species studied.

Celosia height was highly variable, but the response curve showed a similar
response under higher temperatures to Salvia and Impatiens. However, at lower
temperatures, increasing DLI had a much more dramatic affect on increasing plant

height, which could be explained by more nodes developing before plants reached

46

ﬁnish stage. Celosia leaves were smaller and chlorotic under the cooler temperatures,
so they did not reach the speciﬁed 4.5 cm plant width until they had developed several
more nodes. Thus, a better developmental point to determine Celosia as “ﬁnished”
would have been more appropriate in this study.

Early ﬂower initiation, such as during the seedling plug stage, can decrease time
to ﬂower in subsequent growth environments. High percentages of visible ﬂower bud
were observed at the ﬁnish plug stage in T agetes and Impatiens in most temperature and
DLI combinations. In contrast, Salvia and Celosia had very low percentages at the
time of ﬁnish. For all species studied, however, visible bud percentage was greatest
when plugs were grown under the highest DLIs and coolest temperatures.
Reproductive seedlings will reach ﬂowering earlier than seedlings that are vegetative,
which can be desirable for greenhouse growers who want rapid ﬂowering in a ﬁnish
container. However, this may not be beneﬁcial in cases where more vegetative growth
is desired before ﬂowering occurs, such as when seedlings are transplanted into large
ﬁnish containers.

Responses to temperature and DLI are truly unique to each bedding plant
species, although some trends among species can be observed. This information will
enable bedding plant growers to better predict the timing of their plugs, which is
extremely important due to large volumes of plugs produced in short periods of time,
when heating is expensive, and natural light intensities are increasing in the months of
January through April. Additionally, this information will allow growers to better
predict quality of plugs at ﬁnish when grown under a wide range of greenhouse

temperature and DLI combinations.

47

Literature Cited

Adams, S.R., S. Pearson, and P. Hadley. 1997. The effects of temperature,
photoperiod and light integral on the time to ﬂowering of pansy cv. Universal violet
(Viola xwittrockiana Gams.). Ann. Bot. 80(1):107-112.

Adams, S.R., S. Pearson, P. Hadley, and W.M. Pateﬁeld. 1999. The effects of
temperature and light integral on the phases of photoperiod sensitivity in Petunia
xhybrida. Ann. Bot. 83(3):263-269.

Armitage, A.M., W.H. Carlson, and J.A. Flore. 1981. The effect of temperature and
quantum ﬂux density on the morphology, physiology, and ﬂowering of hybrid
geraniums Pelargonium xhortorum. J. Amer. Soc. Hort. Sci. 106(5):643-647.

Dressen, DR. and R.W. Langhans. 1992. Temperature effects on growth of impatiens
plug seedlings in controlled environments. J. Amer. Soc. Hort. Sci. 117(2):209-215.

Faust, J.E. and RD. Heins. 1997. Quantifying the inﬂuence of high-pressure sodium
lighting on shoot-tip temperature. Proc. Third Int. Simp. Artiﬁcial Lighting. Acta
Hort. 418:85-91.

Graper, DP. and W. Healy. 1990. Synergistic acceleration of Begonia semperﬂorens
development using supplemental irradiance and soil heating. Acta Hortic. 272:255-
259.

Graper, DP. and W. Healy. 1991. High pressure sodium irradiation and infrared
radiation accelerate Petunia seedling growth. J. Amer. Soc. Hort. Sci. 116(3):435-438.

Kessler, R., A.M. Armitage, and D. Koranski. 1990. Effect of supplemental light and
duration of exposure on growth and ﬂowering of Begonia semperﬂorens. Acta Hortic.
272:137-144.

Pietsch, G.M., W.H. Carlson, R.D. Heins, and J .E. Faust. 1995. The effect of day

and night temperature and irradiance on development of Catharanthus roseus (L.)
'Grape Cooler'. J. Amer. Soc. Hort. Sci. 120(5):877-881.

48

Table 1. Actual temperature recorded in geenhouse sections.

 

Average soil temperature (°C) Average air temperature ( oC)
Replication (Under ambient conditions)

 

 

 

14 17 20 23 26 14 17 20 23 26
1 14.4 17.4 19.2 24.0 26.0 14.5 16.7 20.2 23.7 26.3
2 17.0 18.4 19.9 24.5 26.7 16.6 17.6 20.6 25.4 27.3

 

Table 2. Actual daily light integral (DLI) recorded in geenhouse sections.

 

 

Average DLI

Replication Treatment (mol-m‘z-d")
1 Ambient light plus 50% shade cloth 4.1
' Ambient 8.6
Ambient plus HPS 15.5
2 Ambient light plus 50% shade cloth 10.8
Ambient 19.4
Ambient plus HPS 24.1

 

49

Table 3. Signiﬁcance of temperature (T), daily light integral (DLI), and their
interaction (T*DLI) to the models developed for Celosia, Impatiens, Salvia, and
T agetes at ﬁnish.

 

 

 

 

 

 

Days to ﬁnish Dry weight Height Node number
Celosia
T ***Z *** *** ***
DLI *** *** *** ***
T*DLI * *** *** *
Impatiens
T *** *** *** ***
DLI *** *** =10!qu *4";
T*DLI *** NS #3101! ***
‘ Salvia
T *** *** *** ***
DLI NS *** *** ***
T*DLI NS *** *alult ***
Tagetes
T *** *** *** ***
DLI NS *** #3101! ***
T*DLI NS *** ** NS

 

zNS, *, **, *** Nonsigniﬁcant or signiﬁcant at P S 0.05, 0.01, 0.001, respectively.

50

Days to ﬁnished plug

60

  
 
 
 
  
     

Eh
O
1

A
o
1

U)
o
1

 

 

 

 

 

 

 

 

 

 

 

 

23 20

26 Temperature (°C)

Figure 1. Response surface for Celosia days to ﬁnish

as a function of average daily temperature (T) and average daily
light integral (DLI). Celosia was considered to be ﬁnished
when the plug was at the fourth leaf stage and reached 3.5 cm
in width. The equation for the response surface was

y— = 111. 901 - 3. 257l6T- 1. 41259DLI + 0. 04514T*DLI with
R2 = 0. 96.

51

 

 

 

 

 

 

 

 

 

 

 

 

@010 "Z
ED 0 08 ‘ ii ' A k ' 1i , i
<1) - ~ ’ ‘
i 0.06‘ . 3f
5 i ' A ‘ .. ’ i
0.04- _ 0 ' * .
11 " ‘
0.02— /
- ilk ' .    ’1 " ‘J ~30
0.00‘ x, ~ ~ ‘ 25
,1 *. , ‘ ‘ 20 \
17 _ , , 4 A .
20 ’ ' “ ’ 15 3 8
Te ‘ \‘9
[are 0 5 9X2
(C) 29

Figure 2. Response surface for Celosia dry weight as a
function of average daily temperature (T) and average daily
light integral (DLI). The equation for the response surface was
y = -0. 19702 + 0.01817T + 0.00749DLI - 0.00037254TQ

- 0.00023343T*DLI with R2 = 0.54.

52

 

 

 

 

 

Height (cm)

 

DJ

 

 

 

 

1 ii'

25 H

20

C(10)] 15
010]? 10
0') 5

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3. Response surface for Celosia height as a function
of average daily temperature (T) and average daily light
integral (DLI). The equation for the response surface was

y= 2.50443+ 0.13542DLI+ 0.00342T2+ 0.00223DLI-
0.00951T*DLI with R2 = 0.17.

53

16 ‘x ;_

    
   
 

'

14- ,

Mil-

 

 

 

 

 

12 . , ¢
41 I; A A l +
:12 10- i' A‘) q _ A ”1%?“
e .. r/ .471. . /
a A 71‘ ' A} , /
Q) 8 T 0 41 ‘ [.1.—«7‘ ”a ;
“U ’4‘ 711“ ﬂ/
0 / l * J”
z , , ,_ _ /
6 A It / F} A ’/
Ai/ *‘ [I A A
-—- ‘ k
A‘ fﬁﬁd:~ﬁt NA’J/ .
A i 3 U A it
4 A , 4, A I
ll

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4. Response surface for Celosia node number at ﬁnish
as a function of average daily temperature (T) and average daily light
integral (DLI). The equation for the response surface was

y= 29.329-1.75315T+ 0.25702DLI+ 0.03216TQ-0.00865T*DLI
with R2: 0.65.

54

Visible bud percentage

100 ~

 

 

 

 

 

 

 

 

80 -
A
60 . A- Ar-
40 - i
l A
, 4 .
201 i
t ' .
‘ 1 1M“ " s 0
0‘ A A“ i " A2] A" h
29 26 , A A.. .. i . . I .1
17 0
Temperature (°C) DL‘ (m

Figure 5. The inﬂuence of temperature and daily light integral
(DLI) on visible bud percentage at the ﬁnish plug stage in Celosia.

55

Days to ﬁnish

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

‘ ’ « i ' r4 if.”
f . . 7 g! , ~ ‘ ”\i y, \
_ ~.JI»< 7V \
20 ‘ ’ , ‘ ' ~\ 1 . ‘ ,
'\ > _ b _
10 ' . ‘ p 14
15 ' 20 17
oél 20 23 KC)
02) 25 ewe
0'} 29 10““6

Figure 6. Response surface for Impatiens days to ﬁnish

as a function of average daily temperature (T) and average daily
light integral (DLI). The equation for the response surface was

y— = 185. 41233 - 11.27041T- 1. 53677DLI + 0. 20366T2 +
0. 05670T*DLI with R2 = 0. 96.

56

0.10 4

 

 

 

 

 

 

 

 

 

 

 

 

 

0 ti T
i“ ‘ . 11
A
008 F i! i L 4‘:
.. w C/
an A A A it ‘
H 0.06 , I x n
in / :1
>5 0.04
H
D
0.02 i 14
l 17 \
0 00 5 20 {O
, 0
10 23 6‘9}
15 26 Qe}
”201mg 25 29
‘1")

Figure 7. Response surface for Impatiens dry weight at ﬁnish
as a function of average daily temperature (T) and average daily
light integral (DLI). The equation for the response surface was
y = 0.10154 - 0.00651T + 0.00245DLI + 0.0001202'1‘2

- 0.00005133DL12 with R2 = 0.39

57

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6 I
it i
5 ‘1 t 1‘ it 1
L 1i /A it. 1
A A ‘ ii I 4r
E ‘v. ' ‘ '4 I/‘I ‘ ‘
3 4 A» f it/ “/t- 1 ”E”
H 414 . , ‘
"ED hZ/“A// ii 1:
E 3 7i/ ‘jﬂ\7L‘ f “I"
4: i k " n \
2 A ‘ 7AA} A I ' 26 00
ii * 77W 1 23 ok
1 Z 3; " 20 {17$
20 i. 1 Q?
15 10 l 17 we
DL 14
[(Inolm-Zdﬂ) 5

Figure 8. Response surface for Impatiens height at ﬁnish
as a function of average daily temperature (T) and average daily
light integral (DLI). The equation for the response surface was

y= 5.896504 - 0.421892T + 0.065601DLI + 0.014178'IJ
+ 0.002082DLI2 - 0.007713T*DLI with R2: 0.39.

58

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

T
8 M if" .
N f
o \ ~ >  ‘
7% 5 '4 >5”,
Q) “\>B/ ‘ 11“."
"g 4 z. A
z “ ‘  A
2 ' \_\
25 ‘ .
20 _ 29
’ " 26
OQK 15 ‘ .. __ 23
0’0! 10 CO
1))? 20 K036
s99

14

Figure 9. Response surface for Impatiens node number at ﬁnish

as a function of average daily temperature (T) and average daily
light integral (DLI). The equation for the response surface was

y = -4.54 + 0.82677T + 0.24486DLI - 00154sz - 0.00786T*DLI

with R2: 0.31.

59

Visible bud percentage

 

100 - 4111(L-~ 1 . ii “if ii" air 7.

m
C
1

05
O
l

h
o
1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 10. The inﬂuence of average daily temperature (T)

and average daily light integral (DLI) on visible bud percentage
at ﬁnish in Impatiens.

60

 

50 I I I I I I l T

. y = 98.8 -4.96x + 0.0829x2
45 " ' ’ ' R2 = 0.83

l

35 --

30 ‘-

Days to Finished Plug

 

 

 

 

l l
20 i i I i I i i i

l4 I6 18 20 22 24 26 28

Temperature (°C)

Figure 11. The inﬂuence of temperature on days to ﬁnished plug
in Salvia. Daily light integral (DLI) did not have a signiﬁcant
effect on days to ﬁnished plug. Plugs were considered ﬁnished
when the second leaf pair reached 3.5 cm in width.

61

Dry weight (g)

0.10 ‘

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.08 ii ' ' [ ' ~
I
'11 ' i
0.06 ‘ i
0 04 V .\ ‘L g
0.02 i -,
/[/V
0.00 i '
25
20 l 29
O 15 26
{if 23
020 10 20 °C)
/ ‘ wek
’12 ‘2)” 5 17 Q6"
14 “V5“

Figure 12. Response surface for Salvia dry weight at ﬁnish

as a function of average daily temperature (T) and average daily
light integral (DLI). The equation for the response surface was
y = 0.057617 - 0.004011T + 0.004607DLI + 0.000095013
T2 - 0.000026618DL12- 0.000108T*DLI with R2 = 0.60.

62

Height (cm)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 13. Response surface for Salvia height at ﬁnish

as a function of average daily temperature (T) and average daily
light integral (DLI). The equation for the response surface was
y = 1.761064 - 0.081501T + 0.158651DLI + 000902318

+ 0.002123DLI2 - 0.012233T*DLI with R2 = 0.55.

63

 

 

 

 

 

 

Node number

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 14. Response surface for Salvia node number at ﬁnish
as a function of average daily temperature (T) and average daily
light integral (DLI). The equation for the response surface was
y = 6.85962 - 0.30447T + 0.00538TQ - 0.00095188DLI2 +
0.00332T*DLI with R2 = 0.39.

100

 

a) 80
89
c.
8
g; 60
9..
-o
.3
2 40 ‘ .
:9. ‘ - . .
.82 . . 29
> 20 . ‘ . ‘ 26 N
. 9 . 23 as»
A 0
0 . i 20 .95
25 20 ‘ . ‘ 047
D 15 10 A ‘ 17 39,
LI( &
I1201m~2 ,1 5 14
d) 0

Figure 15. The inﬂuence of temperature and daily light integral
(DLI) on visible bud percentage at the ﬁnish plug stage inSaIvia

65

Days to ﬁnish

32 I I W I I I I I

 

30 n g y = 35.2 — 0.665x .
r2 = .50
28 «~ 0 -
26 w

24 ‘-

 

 

 

 

Figure 16. The inﬂuence of temperature on days to ﬁnished plug
in Tagetes. Daily light integral (DLI) did not have a signiﬁcant
effect on days to ﬁnished plug. Plugs were considered ﬁnished
when the second leaf pair reached 4.5 cm in width.

66

ht (8)

Dry weig

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.14
0.12 ' i‘
0.10 . 1:
0.08 “
1| _,
0.06 , it” \4 _
0.04 . .. 3
0.02 :_
0.00
25
20 29
0 15 26
Q04) 10 23
0/02? 20 6(0)
., 5 17 1‘3““
0' 9e,
14 16:9

Figure 17. Response surface for T agetes dry weight at ﬁnish
as a function of average daily temperature (T) and average daily
light integral (DLI). The equation for the response surface was

y = 0.05653 - 0.0046OT + 0.00587DLI + 0.00011621
T2- 0.00017692T*DLI with R2 = 0.60.

67

Height (cm)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4r
6 « 4*
4
z i t
5 - , W‘ 77
lg}: A L 1
4 . . ‘F\ . 1 ‘ . '\‘ r
7: H / v
3 ‘ A
VP i\\\i .
25 A 1 ' A >- 29
2 A 26
1 /23
DLI( 1 20 6 CC)
111011)) 2 17 wQeia
d ) 14 13

Figure 18. Response surface for T agetes height at ﬁnish
as a function of average daily temperature (T) and average daily
light integral (DLI). The equation for the response surface was

y- — 4. 85607- O. 21798T2 + 0. 08484DLI + 0. 00802T2
- 0. 000306T*DLI with R2: 0. 46.

68

4.5

DJ
Kl!

 

 

 

 

 

 

 

Node number
b)
O

I"
Ut

 

 

 

 

 

 

 

 

I”
o

 

 

 

 

 

1.5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

14 16‘“?

Figure 19. Response surface for T agetes node number at ﬁnish
as a function of average daily temperature (T) and average daily
light integral (DLI). Each point may represent more than one observation

The equation for the response surface was y = 4.79135 - 0.16583T
+ 0.003551“2 + 0.01463DLI with R2 = 0.10

69

T _ T i
100

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

. T
31) 80 T i T ’ ~‘i
S 1
8 l e i
O
8 60 1‘ ..
Q‘ A
E 40 is A
g /,//w//\~W ‘ i
11”- 20 "i” A \\
> .,
0 l “ l
20 i 29
0 15 26
{f@ 23 oC)
o/ 10 e.K
$29 20 313'
9., 5 17 «to?
14

Fi ure 20. The inﬂuence of temperature and daily light integral
(DLI) on visible bud percentage at the ﬁnish plug stage in T agetes

70

SECTION III

Quantifying the Effects of Temperature and Daily Light Integral on Finish Bedding

Plant Growth and Development

71

Quantifying the Effects of Temperature and Daily Light Integral on Finish
Bedding Plant Growth and Development

Lee Ann Pramukl and Erik S. Runkle2

Department of Horticulture, Michigan State University, East Lansing, MI 48824

Additional index words: Celosia, Impatiens, Salvia, T agetes.

Received for publication . Accepted for publication . We

 

gratefully acknowledge funding from growers providing support for Michigan State
University ﬂoriculture research.

1 Graduate Student. Current address: Michigan State University, Dept. of Horticulture,
East Lansing, MI 48824

2 Assistant Professor of Horticulture and Extension Specialist, to whom reprint

requests should be addressed (Email: runkleer@msu.edu).

72

Introduction

Production of garden plants is of major economic importance to the ﬂoriculture
industry. In 2000, greenhouse growers in the United States produced garden plants
with a wholesale value of $2.12 billion, representing 50% of the wholesale value of all
reported ﬂoricultural crops (USDA, 2001). The production of spring bedding plants in
northern climates in the winter and early spring forces growers to rely on greenhouse
heating. In recent years, fuel prices have ﬂuctuated dramatically, and in response to
energy expenses, growers may reduce their temperature settings to reduce their monthly
fuel consumption. Although these methods may save in short-term fuel costs, crop
timing and plant quality may be compromised in the process.

Daily light integral (DLI) varies by latitude and by time of year. In northern
climates, DLIs can be quite low during winter and early spring. The amount of light
plants receive in a greenhouse is not only affected by the amount of ambient solar
radiation, but also by interference from greenhouse glazing and structures, which can
reduce light by 40%. For example, outdoor light levels in midsummer in East Lansing,
Michigan average about 45 mol-m'z-d'1, and in midwinter average about 10 mol-m'Z-d‘l
(Niu et a1. , 2001a). Thus, a typical greenhouse will transmit at most an average of 6 to
27 mol-m'z-d'l during the year. Under lower light levels, growers may consider the use
of supplemental lighting to improve plant quality. However, whether the beneﬁts of
supplemental lighting outweigh the economic costs has not been determined for many
bedding plants primarily because the effects of DLI on plant growth and development

have not been determined.

73

Due to the value of bedding plants and the need for energy efﬁcient production,
the growth and development of bedding plants must be well understood and quantiﬁed.
The effects of temperature and DLI have been studied on some economically important
bedding plants, such as petunia (Petunia xhybrida Hort.Vilm.-Andr.), pansy (Viola
xwittrockiana Gams.), vinca (Catharanthus roseus L.), and seed geranium
(Pelargonium xhortorum Bailey) (Adams et al., 1997; 1999; Armitage et al. , 1981;
Pietsch et al. , 1995). Although these studies provide information on plant response to
temperature and light intensity, more research in this area is warranted due to the
variability of optimum temperatures and light requirements among species and between
developmental processes. Additionally, to our knowledge, few recent scientiﬁc studies
on temperature and DLI interaction have been published on other economically
important ﬂoricultural crops, such as impatiens (Impatiens wallerana Hook.f.) and
marigold (T agetes patula L.).

The objectives of this research were to quantify the effects of temperature and
DLI on progress to ﬂowering and plant appearance at ﬂowering (dry weight, height,
node number, ﬂower number, and ﬂower size) of four popular bedding plants: Celosia,
Impatiens, Salvia, and T agetes.

Materials and Methods

Seedling plug culture. Seeds of Celosia argentea var. plumosa L. ‘Gloria Mix’,
Impatiens wallerana Hook.f. ‘Accent Red’, Salvia splendens F. Sello ex Roem &
Schult. ‘Vista Red’, and T agetes patula L. ‘Bonanza Yellow’ were sown in 288-cell

plug trays on 25 January 2002 and 2 April 2002 at a wholesale plug producer (Raker’s

74

Acres, Litchﬁeld, Mich.). The germinated seeds were received at Michigan State
University on 29 January 2002 and on 8 April 2002. The 288-cell trays were placed in
a growth chamber set at 23 °C under 150 umol-m'Z-s“ provided by incandescent and
ﬂuorescent lamps with a 16-h photoperiod. Chambers were set at a vapor pressure
deﬁcit of 0.7 kPa. Plugs were top irrigated with well water (containing 95, 34, and 29
mg-L“ Ca, Mg, and S, respectively) supplemented with a water soluble fertilizer to
provide the following (mg-L"): 40 N, 4 P, 40 K, 5 Ca, 0.3 Fe, 0.03 B and Mo, and 0.2
Mn, Zn, Cu (MSU Special; Greencare Fertilizers, Chicago, IL). Water was acidiﬁed
with H2804 to a titratable alkalinity of ~140 mg-L’l CaCO3. Seedling were grown until
deemed ready for transplant, which was 19, 23. 26, and 26 days from seed, for

T agetes, Impatiens, Salvia, and Celosia, respectively.

Greenhouse temperature and DLI treatments. For each species, 150 seedlings
were removed from the growth chamber and transplanted into lO-cm pots containing
70% peat moss, 21% perlite, and 9% vermiculite (SUREMIX, Michigan Grower
Products, Inc., Galesburg, Mich). Plants were placed into 5 glass greenhouse
compartments set at constant 14, 17, 20, 23, and 26 °C. Greenhouse air temperature
was measured by a thermocouple placed in an aspirated box, and shoot tip temperature
was measured by a thermocouple inserted 2:2 mm below a plant shoot-tip under ambient
light conditions. Within each compartment, ten pots were placed under each of three
DLI treatments: ambient light with 50% shade cloth (OLS 50; Ludvig Svensson,
Charlotte, NC), ambient light, and ambient plus supplemental lighting from high

pressure sodium lamps (z170 umol-m’zs"). Plants in all treatments were exposed to a

75

16-h photoperiod, from 0600 HR to 2200 HR, using HPS lamps which delivered 2:34,
z75, z170 umol-m'zs under the ambient light plus 50% shade cloth, ambient light, and
ambient plus supplemental high-pressure sodium, respectively. Line quantum sensors
(Apogee Instruments, Inc. Logan, Utah) were placed under the three lighting treatments
in three of the ﬁve greenhouse compartments to measure photosynthetic photon ﬂux
(PPF). Instantaneous values were converted to daily light integrals (DLI), which were
used for analysis. Vapor pressure deﬁcit was maintained at 240.7 kPa by steam
injection. A CR10 data logger (Campbell Scientiﬁc, Logan, Utah) recorded the
environmental data every 10 seconds and hourly averages were reported (Table l and
2).

Plants were top irrigated as necessary with well water (containing 95, 34, and
29 mg-L‘l Ca, Mg, and S, respectively) supplemented with a water soluble fertilizer to
provide the following (mg-L"): 125 N, 13‘ P, 125 K, 15 Ca, 1 Fe, 0.1 B and Mo, and
0.5 Mn, Zn, Cu (MSU Special; Greencare Fertilizers, Chicago, IL) acidiﬁed with
H280, to a titratable alkalinity of 140 mg-L" CaCO3. Date of ﬂower, plant height from
soil level, node number on the primary shoot, total shoot dry weight, ﬂower number,
and ﬂower size were recorded at open ﬂower. T agetes and Impatiens were considered
open when all petals were fully reﬂexed. Celosia was considered in ﬂower when the
inﬂorescence reached 4 cm long, and Salvia when the bottom ﬂoret was open.

Data were analyzed using average air temperature and DLI for each individual
plant from transplant to ﬂowering. Flowering data were converted to rates by taking the

reciprocal of number of days to ﬂowering. Multiple regression analysis was performed

76

using SAS (SAS Institute Inc., Cary, NC) response surface regression (RSREG
procedure) to determine the effect of DLI in combination with air temperature. Similar
studies with temperature and DLI have used similar forms of analysis (Adams et al.
1997; Carew et al. , 2003). If P > 0.05 for the contribution of individual terms to the
model, the terms were removed, and regression (REG procedure) was used to
determine the model coefﬁcients. Equations were then used to generate predicted
models. Approximately 300 observations were used to generate each model. Base
temperatures, under 5 and 15 moltm‘z-d" , were calculated by inserting the appropriate
DLI into the rate of progress to ﬂower equation and setting the equation equal to zero.
Results

Celosia. Rate of progress to ﬂowering was related quadratically with
temperature and DLI (Table 3). Within the range of observed DLI, rate of progress to
ﬂowering increased up to z25 °C (Fig. 1). Increasing the DLI from 5 to 15 mol-m'z-d",
accelerated ﬂowering rate, but further increases in DLI had a negligible effect on rate
of progress to ﬂower. The model predicted days to ﬂower within i 5 days for 68% of
the actual data (Fig. 6). Calculated base temperatures under 5 and 15 mol-m'z-d'l were
11.7 and 10.2 °C, respectively.

Plant height was primarily affected by temperature, increasing with increasing
temperature and the largest differences in height due to DLI were observed at 28 °C
(Fig. 2). Dry weight increased as temperature and especially DLI increased (Fig. 3).
For example, at 14 °C, plants under 5 mol-m'2~d’l averaged 1.6 g while those under 25

mol-m‘ztd'l averaged 5.8 g. Node number at ﬂowering was greatest in plants that

77

received 25 mol-m‘z-d", but differences in node number in plants receiving < 20 mol-m'
2-d” were small (Fig. 4). However, node number had a low coefﬁcient of
determination (R2: 0.23) (Table 3). Under 25 mol-mad", ﬂower number was greatest
at z22 oC, and began to decrease as temperature increased or decreased (Fig.5). Under
5 mol-m'zd'l , ﬂower number was maximal at z16 °C, and decreased as temperature
increased to 28 °C. Flower size was not recorded for Celosia, as the length of the
inﬂorescence was used to determine when plants were in ﬂower.

Impatiens. Rate of progress to ﬂowering increased quadratically as temperature
increased from 14 to 28 °C (Fig. 7). The model predicted days to ﬂower within i 5
days for 70% of the actual data (Fig. 6). Base temperatures calculated under 5 and 15
mol-m’z-d'l were 7.5 and 4.3, respectively.

Plant height at ﬂowering increased under all DLIs as temperatures increased
from 14 to 21°C and decreased thereafter (Fig. 8). Additionally, plant height increased
as DLI increased at all temperatures studied. However, the coefﬁcient of determination
for the model was relatively low (R2=0.21). Dry weight increased as DLI increased at
all temperatures studied; at 20 °C, dry weight was z72% less under 5 than 25 mol-m‘z-d‘
' (Fig. 9). Node number was not recorded for Impatiens. Flower size decreased as
temperature increased from z15 °C to 28 °C, and the effects of DLI were relatively
small (Fig. 10). Flower number decreased with increasing temperature and increased
with increasing DLI. For example, at 14 °C, ﬂower number increased by z88% as DLI
increased from 5 to 25 mol-m‘z-d", and at 26 oC, ﬂower number increased by z330%

(Fig. 11).

78

.m— ..

Salvia. Rate of progress to ﬂower increased quadratically as temperature and
DLI increased, and an optimum temperature was not observed in the temperatures
tested (Fig. 12). The model predicted days to ﬂower within 1‘ 5 days for 90% of the
actual data (Fig. 16). Base temperatures calculated under 5 and 15 mol-m'z-d" were 7.3
and 6.8 °C, respectively.

Plant height increased with temperature under all DLIs until a maximum at z20
°C under 5 mol-m’z-d" and at -~24 °C under 25 mol-m’Z-d"; beyond that maximum, plant
height decreased (Fig. 13). However, the R2 value was low (0.21). Plant height
decreased with increasing DLI at temperatures ranging from 14 through 26 °C. Dry
weight increased as temperature decreased regardless of DLI (Fig. 14). Node number
at ﬂowering and ﬂower size were not signiﬁcantly affected by temperature or DLI (data
not presented). Flower number generally decreased with increasing temperature, but
was between 9 and 11 when temperature was S 20 °C (Fig. 15).

T agetes. Rate of progress to ﬂowering increased as DLI and temperature
increased (Fig. 17), and an optimum was not reached in the observed temperature
range. The model predicted days to ﬂower within i 5 days for 91% of the actual data
(Fig. 16). Base temperatures calculated under 5 and 15 mol-m‘z-d‘l were both -3.9 °C.
Plant height increased linearly with increasing temperature and DLI, although the r2
value was low (0.23) (Fig. 18). Dry weight was greatest at the coolest temperatures
and highest DLI, and decreased with increasing temperature (Fig. 19). At 14 °C, dry
weight increased by 100% as DLI increased from 5 to 25 mol-m'z-d". Flower number

and ﬂower size both decreased linearly as temperatures increased from 14 to 28 °C and

79

DLI decreased from 25 to 5 mol-m'Z-d‘l (Fig. 20 and 21). Under 25 mol-mad", ﬂowers
were 84% smaller and 42% fewer when they ﬂowered at 28°C compared with plants
grown at 14 °C.
Discussion

Days to ﬂowering was signiﬁcantly affected by both temperature and DLI in all
species. In the observed temperature and DLI ranges, Topt were observed in Celosia
(~25 0C) and Impatiens (z26 °C), but not in Salvia and T agetes. Increasing the DLI
increased progress to ﬂowering in Salvia and T agetes, but above 15 mol-m'z-d", there
was little increase in rate progress to ﬂower in Celosia. The effect of DLI on Impatiens
varied with temperature, and at >20 °C, the model predicts a delay in ﬂowering at > 15
mol-mid". This may indicate a maximum in photosynthetic capacity for these plants,
which is not surprising since Impatiens can be considered a shade-tolerant plant.

The increase in rate of progress to ﬂower attributed to DLI for these species
may be at least partially due to increased plant temperature under the higher DLI
treatments. Studies on vinca (Catharanthus roseus L.) showed that shoot tip
temperature can be greater than air temperature when under higher light intensities
(Faust and Heins, 1997). Shoots receiving supplemental HPS lighting of 50, 75, and
100 umol-m’z-s’l were 1.2, 1.5, and 1.7 °C higher, respectively, than that of plants in
the dark (Faust and Heins, 1997). Because node number was not signiﬁcantly
inﬂuenced by temperature or DLI in Salvia or T agetes (data not shown), the differences
in time to ﬂower could primarily be a function of plant temperature. In contrast,

temperature and DLI inﬂuenced node number at ﬂowering in Celosia. Node number

80

below the inﬂorescence of Celosia increased as temperature increased from 20 to 28 0C,
and was also greater under the highest DLIs, although the coefﬁcient of determination
was quite low (r2 =0.20). Additionally, low light can affect plant development by
limiting the supply of photosynthate. This could also be a contributing factor to
decreases in rate of ﬂowering under the lower light levels.

The models developed varied in accuracy, with Salvia and T agetes generally
being the most accurate (> 90% of the actual data was within 1: 5 days of the predicted),
and Celosia and Impatiens containing more variability. Actual days to ﬂower was
greater than predicted in the models for Celosia and Impatiens as evidenced by the
skewed frequency diagrams. Some of the variability may be explained by genetic
variability within the seed populations. Additionally, the selected cultivar for Celosia
was ‘Gloria Mix’, which may have had more variability than if a single color cultivar
had been studied. Further independent experimentation could be performed to
strengthen the validity of each model.

Dry weight at ﬂower increased as DLI increased from 5 to 25 mol-m‘z-d'l in all
species, except for Salvia, which reached an optimum dry weight under z15 mol-m‘z-d'
'. Dry weight also decreased with increasing temperature in all species except for
Celosia. A previous study on campanula showed similar results; as average daily plant
temperature decreased from 25 to 15 °C, dry weight decreased linearly under a DLI of
10.8 and 15.8 mol-m’Z-d" (Niu et al., 2001b). Dry weight increased by z155% when

DLI increased from 4.2 to 10.8 mol-m'Z-d'l and by 25% when DLI increased from 10.8

to 15.8 mol-m‘Z-d‘l (Niu et al., 2001b). In contrast, in our study with Celosia, dry

81

weight increased with increasing temperature. This may be explained by the chlorotic
growth that was observed at cooler temperature treatments, indicating a decreased
ability to harvest light. This is likely why dry weight increased with temperature,
especially at the higher DLIs, even though plants grew for a longer period of time
before ﬂowering at the cooler temperatures.

Flower number at ﬁrst open ﬂower generally decreased as temperature
increased because time to ﬂowering was reduced as temperature increased. Thus,
plants had a longer duration to produce photosynthates when grown at the cooler
temperatures which could be used for ﬂower production. In previous studies with
coreopsis (Coreopsis grandtﬂora Hogg ex Sweet. ‘Sunray’), rudbeckia (Rudbeckia
fulgida Ait. ‘Goldsturm’), and Shasta daisy (Leucanthemum xsuperbum Bergman ex. J.
Ingram ‘Snowcap’), ﬂower bud number at time of ﬂowering decreased 80% , 75%, and
55% , respectively, as temperature increased from 16 °C to 26 °C (Yuan et al., 1998).
In campanula (Campanula carpatica Jacq. ‘Blue Clips’), the number of ﬂower buds
decreased linearly, at 10 ﬂowers per °C, as plant temperature increased from 16 to 24
°C (under ambient CO2 concentration) (Niu et al., 2001). Our data suggest a similar
response, with ﬂower number decreasing as temperature increased in all four bedding
plant species. Additionally, in Celosia, Impatiens, and T agetes, ﬂower number
increased as DLI increased at all temperatures studied. However, ﬂower number of

Salvia began to decrease when temperature was below z20 0C and DLI was >15 mol-m‘

2.d-l.

82

Flower size was not signiﬁcantly inﬂuenced by temperature or DLI in Salvia
and was not measured in Celosia as length of the ﬂower was used to determine time of
ﬂower. Flower size of Impatiens and T agetes increased as temperature decreased.

This can also be explained by the ability of plants to harvest increasingly more light at
the lower temperatures, since the rate of progress to ﬂower was slower at the lower
temperatures. Increasing the DLI also increased ﬂower size of Impatiens and T agetes,
but in Impatiens, it reached a maximum between 10 and 15 mol-mad". Other studies
indicate similar relationships. In campanula, at temperatures ranging from 14 to 26 °C,
ﬂowers were z10-15% larger under 17 than under 5 mol-m‘Z-d'l (Niu et al., 2001).
Similarly, ﬂower size in vinca was 1.5-20% greater when plants were grown under a
DLI of :29 mol-m'z-d" at temperatures ranging from 15 to 35 °C, compared with plants
under z18 and z9 mol-m'Z-d" (Pietsch et al., 1995). In geranium ‘Sooner Red’, ﬂowers
were smaller under shade than under ambient conditions (Armitage and Wetzstein,
1984).

Except for T agetes, the estimated base temperature for rate of progress to
' ﬂowering for these species differed under different DLIs, with the largest difference
occurring in Impatiens (3.2 °C) as DLI increased from 5 to 15 mol-m'Z-d". T agetes had
the lowest base temperature of the species studied at -3.9 °C. Salvia (7.3 and 6.8 °C)
and Impatiens (7.5 and 4.3 °C) had similar base temperatures and Celosia had the
highest base temperatures (11.7 and 10.2 0C). If short-term heating costs were of
concern, T agetes, Impatiens, and Salvia could be grown cooler, and higher quality

could be obtained, although time to ﬂower would be increased. However, Celosia,

83

having a much higher base temperature, could not be successfully produced under
cooler temperatures, so warmer temperatures >20 °C would be recommended.

Supplemental lighting could be beneﬁcial for all species under naturally low
light levels to reduce days to ﬂower and in most cases, increase quality. For Celosia,
hastening of ﬂowering only occurred with DLIs up to 15 mol-m‘z-d". So, if natural light
levels are already moderately high, supplemental lighting would have little or no effect
on time to ﬂower. Similarly, in Impatiens, at temperatures >20 °C, the model predicted
that a DLI >15 mol'm'Z-d'l delayed time to ﬂower, so supplemental lighting would not
be beneﬁcial. For Salvia and T agetes, time to ﬂower continued to decrease with
increasing DLI to 25 moltm'Z-dJ, which was the greatest DLI recorded in these
experirnents.

Increasing daily light integral may be beneﬁcial for decreasing time to ﬂower
and improving plant quality, but the economic costs to install and maintain
supplemental lighting should be considered. Using a ﬁnancial lighting model presented
by Fisher and Donnelly (2002), we developed an economic scenario to demonstrate
how timing information can be utilized. If a crop of Celosia were grown at 20 °C and
the DLI was z5 mol-m'zod“, it would take 43 days to ﬂower. With an additional 5
mol-m'Z-d", it would take 37 days to ﬂower. Assuming the use of 400W HPS lamps,
lighting for 16 weeks per year, the lamps lasting 15 years, and the bulbs lasting 12,000
hours, the cost without lighting amounts to $0.92/ft2/crop and with lighting,

$1 .58/ft2/crop (Table 4). The cost to install lamps and provide electricity would exceed

84

the amount of overhead one would save by increasing the crop time, so lighting would
not be beneﬁcial in this scenario.

The information presented here can allow growers to predict crop timing and
plant quality under a wide range of temperatures and DLIs in 4 bedding plant cultivars.
This information can then be used to weigh the costs and beneﬁts of timing and quality

with economic costs.

85

 

Literal

Adams
photop
(Viola

Adams
temper.
xhj‘bric

Armita
quantln
geranit

Armita
initiatic

Carew,
temper
8T0W1h
128(3):

Faust,
lightin;

Fisher,
illVesu
HOI'tic

Niu, c
PEFCnI

Niu, c
tempe]
develo

Pictsci
and nil
'Grape

Literature Cited

Adams, S.R., S. Pearson, and P. Hadley. 1997. The effects of temperature,
photoperiod and light integral on the time to ﬂowering of pansy cv. Universal Violet
(Viola xwittrockiana Gams.). Ann. Bot. 80(1):107-112.

Adams, S.R., S. Pearson, P. Hadley, and W.M. Pateﬁeld. 1999. The effects of
temperature and light integral on the phases of photoperiod sensitivity in Petunia
xhybrida. Ann. Bot. 83(3);263-269.

Armitage, A.M., W.H. Carlson, and J.A. Flore. 1981. The effect of temperature and
quantum ﬂux density on the morphology, physiology, and ﬂowering of hybrid
geraniums Pelargonium xhortorum. J. Amer. Soc. Hort. Sci. 106(5):643-647.

Armitage, A.M. and H.Y. Wetzstein. 1984. Inﬂuence of light intensity on ﬂower
initiation and differentiation in hybrid geranium. HortScience 19(1):]14-116.

Carew, J .G., K. Mahood, J. Darby, P. Hadley, and NH. Battey. 2003. The effect of
temperature, photosynthetic photon ﬂux density, and photoperiod on the vegetative
growth and ﬂowering of ‘Autumn Bliss’ raspberry. J. Amer. Soc. Hort. Sci.
128(3):291-296.

Faust, J.E. and RD. Heins. 1997. Quantifying the inﬂuence of high-pressure sodium
lighting on shoot-tip temperature. Acta Hortic. 418:85—91.

Fisher, PR, and C .S. Donelly. 2002. Development of a ﬁnancial model to evaluate
investment in supplemental lighting for greenhouse ﬂoricultural production. Acta
Hortic. 580:191-196.

Niu, G., E. Runkle, R.D. Heins, A. Cameron, and W. Carlson. 2001a. Herbaceous
perennials: light. Greenhouse Grower. 134-143.

Niu, G., R.D. Heins, A.C. Cameron, and W.H. Carlson. 2001b. Day and night
temperatures, daily light integral, and C02 enrichment affect growth and ﬂower
development of Campanula carpatica ‘Blue Clips’. Scientia Hortic. 87:93-105.

Pietsch, G.M., W.H. Carlson, R.D. Heins, and J .E. Faust. 1995. The effect of day
and night temperature and irradiance on development of Catharanthus roseus (L.)
'Grape Cooler'. J. Amer. Soc. Hort. Sci. 120(5):877-881.

Yuan, M., W.H. Carlson, R.D. Heins, and AC. Cameron. 1998. Effect of forcing
temperature on Coreopsis grandiﬂora, Gaillardia xgrandiﬂora, Leucanthemum
xsuperbum, and Rudbeckia fulgida. HortScience 33(4):663—667.

86

Table 1. Air temperature and average shoot-tip temperature of plants (T agetes) under
ambient light treatments grown in glass greenhouses at the indicated setpoints.

 

 

 

 

Replication Shoot-tip temperatures °C Air temperatures °C
14 17 20 23 26 14 17 20 23 26
1 16.1 17.4 20.5 23.3 26.4 15.1 17.4 20.3 24.2 26.7
2 17.7 18.9 20.5 25.7 26.9 16.8 17.6 20.7 25.5 27.1

 

 

Table 2. Daily light integral (DLI) under treatrnents.
Average DLI

 

 

Replication Treatment (mol-m'Z-d")
1 Ambient light plus 50% shade cloth 7.6
Ambient 15.8
Ambient plus HPS 21.6 __
2 Ambient light plus 50% shade cloth 11.4
Ambient 21.2
Ambientjlus HPS 25.6

 

 

87

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88

Table 4. Theoretical example of the cost of supplying an additional 5 mol-m‘z-d'l of
HPS lighting to Celosia grown at 20 °C. Assuming 4” plant spacing, electricity costs
= $0.099/ft2/wk and overhead from lamp installation and maintenance =
$0.051/ft2/wk. Financial information and assumptions taken from Fisher and Donnelly,
2002.

 

 

 

 

 

 

 

Lighting Overhead Total cost
DLI Days to cost per ft2/ cost per ftz/ per ftz/
Scenario (mol-m‘zod“) ﬂower week week crop
Natural light 5 43 0 $0.15 $0.92
Supplemental 10 37 $0.149 $0.15 $1.58
light

 

 

 

89

 

 

0
0

ll.\

.0.

. . 0
0 0

C

Fig

of]
in'

0. 06

0.05 ‘ g 5‘
0.04 0' i ‘

 

1/ Days to ﬂower

 

Figure 1. Temperature and daily light integral effects on Celosia rate
of progress toward ﬂowering. The model was generated using the coefﬁcients
in Table 3.

35.

 

30‘

N
LII

Height (cm)
'5’

15‘

 

10" ‘

 

 

  
    
 
  
 

I

29

 

6
3

      
 

O

 

  
    

20 °C)
7
D 15 10 5 14 etawxe K
LI (mol m‘2 d") '8er

Figure 2. Temperature and daily light integral (DLI) effects on Celosia
height at ﬂowering. The model was generated using the coefﬁcients in Table 3.

91

12

 

e

:3
0.
‘9:

 

Figure 3. Temperature and daily light integral (DLI) effects on Celosia
dry weight at ﬂowering. The model was generated using the coefficients
in Table 3.

92

40

 

to
5?
:

 

Figure 4. Temperature and daily light integral (DLI) effects on Celosia
node number at ﬂowering. The model was generated using the coefﬁcients
in Table 3.

93

Flower number
'5’
: ’

 

 

Figure 5. Temperature and daily light integral (DLI) effects on Celosia
ﬂower number. The model was generated using the coefficients
in Table 3.

94

 

3O ‘— _T ‘— I I I ' I ' r ' I ‘ I I I

 

 

C elosia
25 -
20 ~
>\
O
C.“
Q)
3
C"
O)
I-
u.
l 1 l l 1 1 l L l
I I T I f I I I j I I I
Impatiens
>\
0
I:
Q)
3
D'
Q)
L-
LL.

 

 

 

-20 -l6 -12 -8 -4 0 4 8 12 16 20

Days to ﬂowering difference

Figure 6. Frequency of predicted minus actual days to ﬂower in Celosia and
Impatiens. The total number of plants observed under temperatures ranging from 14 to
26 °C and daily light integrals from 4 to 26 mol-m‘Z-d'l was 296 and 298, respectively.

95

0.08

O. 06

 

0.04

 

 

1/ Days to ﬂower

 

 

0.00

 

 

 

Figure 7. Temperature and daily light integral (DLI) effects on Impatiens
rate of progress toward ﬂowering. The model was generated using the coefﬁcients
in Table 3.

96

Height (cm)

H 9—5
h ON
I I

D

 

 

 

 

 

 

Figure 8. Temperature and daily light integral (DLI) effects on

Impatiens height at ﬂowering. The model was generated using the
coefﬁcients in Table 3.

97

v ,5»
v

 

Dry weight (g)

 

Figure 9. Temperature and daily light integral (DLI) effects on
Impatiens dry weight at ﬂowering. The model was generated
using the coefﬁcients in Table 3.

98

Flower size (cm)

 

Figure 10. Temperature and daily light integral (DLI) effects on
Impatiens ﬂower size. The model was generated
using the coefﬁcients in Table 3.

99

 

 

 

Flower number

 

 

 

Figure 11. Temperature and daily light integral (DLI) effects on
Impatiens ﬂower number. The model was generated
using the coefﬁcients in Table 3.

100

1/ Days to ﬂower

0.06 1

0.05 ‘

 

 

0.04 ‘

0.03 "

0.02 ‘

 

 

0.01‘

 

Figure 12. Temperature and daily light integral (DLI) effects on

Salvia rate of progress toward ﬂowering. The model was generated
using the coefficients in Table 3.

101

 

 

Figure 13. Temperature and daily light integral (DLI) effects on
Salvia height at ﬂowering. The model was generated
using the coefficients in Table 3.

102

 

Dry welght (g)

 

Figure 14. Temperature and daily light integral (DLI) effects on
Salvia dry weight at ﬂowering. The model was generated
using the coefﬁcients in Table 3.

103

 

Flower number

 

Figure 15. Temperature and daily light integral (DLI) effects on
Salvia ﬂower number. The model was generated
using the coefﬁcients in Table 3.

104

 

50 ' I r I I I I I I r I I

 

45 «b Salvia

Frequency

 

.rageres g , ‘ l

Frequency

 

 

 

 

Days to ﬂowering difference

Figure 16. Frequency of predicted minus actual days to ﬂower in Salvia and Tagetes.
The total number of plants observed under temperatures ranging from 14 to 26 °C and
daily light integrals from 4 to 26 mol-m’Z-d’l was 300 and 292, respectively.

105

l/Days to ﬂower

0.08

0.07

0.06

 

0.05

0. 04

0. 03

0.02

0.01

 

Figure 17. Temperature and daily light integral (DLI) effects on

Tagetes rate of progress toward ﬂowering. The model was generated
using the coefﬁcients in Table 3.

106

Height (cm)

18

Figure 18. Tem;

 

 

 

T agetes height. 7
in Table 3.

perature and daily light integral (DLI) effects on
The model was generated using the coefficients

107

Dry weight (g)

 

 

Figure 19. Temperature and daily light integral (DLI) effects on
Tagetes dry weight. The model was generated using the coefficients
in Table 3.

108

Flower size (cm)

 

Figure 20. Temperature and daily light integral (DLI) effects on
T agetes ﬂower size. The model was generated using the coefficients
in Table 3.

109

. . ‘12
35 " 3
32 . . g ‘ h
29

 

7‘?
4% ._
’4’

 

Figure 21. Temperature and daily light integral (DLI) effects on
Tagetes ﬂower number. The model was generated using the coefﬁcients
in Table 3.

110

SECTION IV

Effects of Daily Light Integral on Bedding Plant Plugs and Subsequent Growth and

Development

111

Effects of Daily Light Integral on Bedding Plant Plugs and Subsequent Growth and
Development

Lee Ann Pramukl and Erik S. Runkle2

Department of Horticulture, Michigan State University, East Lansing, MI 48824

Additional index words: Celosia, Impatiens, Salvia, T agetes, Viola.

Received for publication . Accepted for publication . We

 

 

gratefully acknowledge funding from greenhouse growers providing support for
Michigan State University ﬂoriculture research. Additional thanks to David Joeright
for assistance in experimental setup.

' Graduate Student. Current address: Michigan State University, Dept. of Horticulture,
East Lansing, MI 48824

2 Assistant Professor of Horticulture and Extension Specialist, to whom reprint requests

should be addressed (Email: runkleer@msu.edu)

 

112

Introduction

Daily light integral (DLI) is the cumulative amount of photosynthetic light
received and it is expressed in mol-m'z-d‘. DLI varies by latitude and by time of year.
Mean DLI ranges from 5 to 10 mol-m‘z-d'l across the Northern US. in December to 55
to 60 mol-m'z-d'l in the Southwestern US. in May through July (Korczynski et al.,

2002). The primary differences in DLI from May through August occur between the

 

eastern and western US. due to regional weather patterns and elevation. From October 1.
through February, differences occur between the northern and southern US. due to
differences in solar duration and quantum ﬂuxes (Korczynski et al., 2002).

The amount of light plants receive in a greenhouse is reduced by the
interference from greenhouse glazing and structures. For example, the DLI outdoors in
midsummer in East Lansing, Michigan average z45 molm’z-d“, and in midwinter
average le mol-m'Z-d" (Niu et al., 2001). Due to glazing and structures, light
transmission is often reduced by about 40%. Thus, a typical greenhouse in Michigan
will transmit an average of z6 to 27 mol-m'z-d'l during the year.

During the winter months in northern climates, low DLIs may lead to poor plant
quality and slower plant development. For example, in petunia, a DLI of 6.6 rather
than 13 mol-m’z-d‘l increased time to ﬂower by up to 3 weeks (Kaczperski et al., 1991).
Since the advent of plug technology, few scientiﬁc studies have been published on the

effects of daily light integral (DLI) on bedding plant plug growth and development. In

113

addition, the effects of DLI during the plug stage on subsequent bedding plant growth
and deve10pment have not been investigated to our knowledge.

DLI is known to affect dry weight and height. For example, the dry weight of
Petunia xhybrida (Graper et al., 1990;Graper and Healy, 1992; Lieth et al, 1991),
Begonia semperﬂorens (Graper and Healy, 1990), Viola xwittrockiana (Adams et al,
1997), and Pelargonium xhortorum (White and Warrington, 1988) increased as DLI
increased, although the dry weight generally increases at a decreasing rate as DLI
increases. An increase in DLI decreased height in Pelargonium xhortorum (Erickson
et al. , 1980) and Impatiens wallerana (Dressen and Langhans, 1992).

Increasing DLI hastened time to ﬂowering in Pelargonium xhortorum
(Carpenter and Rodriquiz, 1971; Erickson et al., 1981; Armitage and Wetzstein, 1984),
Matthiola incana (Dansereau et al., 1998), and Petunia xhybrida (Kacsperski et al.,
1991). However, increasing DLI from 4 to 16 mol-m'Z-d", did not have an effect on
time to ﬂower in Campanula carpatica (Niu et al. , 2001b).

Quality characteristics such as ﬂower size and ﬂower number can be affected
by DLI. Generally, the number and size of ﬂowers increases as DLI increases. This
trend has been observed in species such as Pelargonium xhortorum (Armitage and
Wetzstein, 1984) and Catharanthus roseus (Pietsch et al., 1995). In Campanula ‘Deep
Blue Clips’, ﬂower size and number were similar when grown under DLIs ranging
from 5 to 17 mol-m'Z-d'l before visible bud (Niu et al., 2001). Supplemental lighting
after visible bud partially compensated for smaller ﬂower number under higher

temperatures; the number of ﬂower buds was z40% higher under 17 mol~m'2.d'l after

114

 

visible bud at 22 to 24 °C than under 5.7 mol-m‘Z-d" at 14 to 16 °C (Niu et al., 2001).
Flower size also increased as DLI increased after visible bud; at temperatures ranging
from 14 to 26 °C, ﬂowers were z10-15% larger under 17 mol-m'z-d'l than under 5
mol-m'z-d‘l (Niu et al., 2001).

Several studies have been published on the effects of DLI from seedling stage
until ﬂowering, but little information is available on the effects of DLI speciﬁcally
during the seedling stage. Goals of this research were to investigate the effects of DLI
on growth, development, and quality of ﬁve popular bedding plant species as young
plants and to determine if there were any residual effects of DLI on subsequent growth
and development after transplant.

Materials and Methods

Initial DLI treatments. Seeds of Celosia argentea var. plumosa ‘Gloria Mix’,
Impatiens wallerana ‘Accent Red’, Salvia splendens ‘Vista Red’ , T agetes patula
‘Bonanza Yellow’, and Viola xwittrockiana ‘Crystal Bowl Yellow’ were sown into 288—
cell trays at a wholesale plug producer (Raker’s Acres, Inc. Litchﬁeld, Mich). Five
days after sowing, trays were delivered and randomly placed in three Conviron E15
growth chambers (Winnipeg, Canada). A high light (HL) chamber was ﬁtted with six
160W ﬂuorescent tubes and ten 25W incandescent bulbs; the medium light (ML)
chamber was ﬁtted with eight ﬂuorescent tubes (four painted black) and ten
incandescent bulbs (four painted black); and the low light chamber was ﬁtted with ten
ﬂuorescent tubes (eight painted black), and six incandescent bulbs (three painted black).

Bulbs were painted black to provide differing light intensities while producing a similar

115

 

thermal load in each chamber. Each chamber was set at z21 °C with minor adjustments
made so that plant temperature was 21°C. A vapor pressure deﬁcit (V PD) of 0.6 kPa
was maintained. In each chamber, air temperature was monitored by an aspirated
thermocouple, plant temperatures were monitored by a thermocouple placed in the
shoot tip, and canopy temperature was monitored by an infrared sensor (IRt/c.01,
Exergen Corp., Watertown, MA) placed at a 45G angle above the canopy. Light
intensity was monitored with a line quantum sensor (Apogee Instruments, Inc. , Logan,
Utah) and a quantum sensor (LI-COR, Lincoln Nebr.). A CRIO data logger (Campbell »
Scientiﬁc, Logan, Utah) recorded the environmental data every 10 seconds and hourly
averages were recorded. Actual average temperature, shoot-tip temperature, VPD, and
DLI from the start of treatments to the end of the plug stage were calculated (Tables 1
and 2). The red (600 to 700 nm) to far-red (700-800 nm) ratio (photons) was
determined each chamber with a spectroradiometer (LI-COR, LI-1800, Lincoln, Nebr.)
and was 3.56, 3.56, and 3.58 for the BL, ML, and LL chambers, respectively. Plugs
were subirrigated with well water (containing 95, 34, and 29 mg-L’l Ca, Mg, and S,
respectively) supplemented with a water soluble fertilizer to provide the following
(mg-L“): 40 N, 4 P, 40 K, 5 Ca, 0.3 Fe, 0.03 B and Mo, and 0.2 Mn, Zn, Cu acidiﬁed
with H2804 to a titratable alkalinity of ~140 mg-L" CaCO3 (MSU Special; Greencare
Fertilizers, Chicago, IL).

Common Environment. Sixteen plugs (8 from each block) of T agetes, Celosia,
Impatiens, Salvia, and Viola were transplanted after 18, 19, 22, 22, and 26 days under

the initial DLI treatments, respectively. Plant height from soil level to shoot apex, node

116

number, shoot dry weight, and visible ﬂower bud (if present) were recorded at
transplant. Plugs were potted into lO-cm pots with a 70% peat moss, 21 % perlite, and
9% vermiculite potting media (SUREMIX, Michigan Grower Products, Inc. ,
Galesburg, Mich.) and randomly placed in a common growth chamber (TC-2
Environmental Growth Chambers, Chagrin Fall, Ohio). Plants were top irrigated as
necessary with well water supplemented with a water soluble fertilizer to provide the
following (mg-L"): 125 N, 13 P, 125 K, 15 Ca, 1 Fe, 0.1 B and Mo, and 0.5 Mn, Zn,
Cu (MSU Special; Greencare Fertilizers, Chicago, IL). Water was acidiﬁed with H280,
to a titratable alkalinity of z140 mg-L“ CaCO3. ‘

The growth chamber was set at 2] 0C, and a DLI of 8.5 mol-m'z-d'l was
provided by ﬂuorescent and incandescent lamps (16-h photoperiod). The vapor
pressure deﬁcit was set at 0.7kPa. DLI was monitored with a quantum sensor (LI-
COR, Lincoln, Nebr.), plant temperature was monitored with thermocouples placed in
the shoot tips, and air temperature was monitored by an aspirated thermocouple.
Temperature and light values were recorded by a CR10 data logger (Campbell
Scientiﬁc, Logan, Utah) every 10 seconds and hourly averages were recorded. The
actual air temperature averaged 21.9 0C. When plants reached ﬂowering, date of ﬁrst
open ﬂower, plant height, node number below the ﬁrst ﬂower, ﬂower number, ﬂower
size, and dry weight were recorded. Salvia was considered in ﬂower when the bottom
ﬂower on the spike opened and Celosia was considered in ﬂower when the
inﬂorescence reached 4 cm in length. The experiment was performed twice, and data

were analyzed using SAS (SAS Institute Inc., Cary, NC) general linear model (GLM

117

procedure). Regression procedures were performed in Sigma Plot (SPSS, Chicago,
Illinois). Average shoot dry weight per average node number was calculated for each
species and used as an indication of plug quality.

Results

Seedling stage. Node number increased as DLI increased from 4.1 to 14.2
mol-m'Z-d'l in all species except for Salvia (Table 3). In Celosia, Impatiens, T agetes,
and Viola, average dry weight per node increased linearly with DLI and by 64%, 47% ,
64%, and 68% respectively, as DLI increased from 4.1 to 14.2 mol-m'Z-d'l (Fig.1).
Salvia dry weight per node increased from 0.006 to 0.014 g-node‘l as DLI inereased
until a maximum at z 12 mol-m'z-d". ‘

Quadratic relationships relating DLI to height were observed in all species
measured (Fig. 2). As DLI increased from 4.1 to 14.2 mol-m’Z-d", height of Impatiens
and Salvia decreased by 27% and 37%. As DLI increased from 4.1 to 14.2 mol-m‘z-d",
height of T agetes increased from 3.1 to 3.4 cm and height of Celosia increased from
2.5 to 2.8 cm. Viola height was not recorded.

Impatiens and Tagetes were the only genera to have visible ﬂower buds at the
time of transplant, and as DLI increased, the percentage of plugs at visible bud
generally increased (Fig. 3). Thirty-eight percent of Impatiens plugs under 14.1 mol-m‘
2-d" were in bud, while plugs grown under 4.1 or 4.5 mol-m'Z-d'I had no ﬂower buds.
All T agetes plugs were in bud at time of transplant under 2 7.2 mol-mad", and only

56% of plants were in bud when grown under 4.1 mol-m’z-d".

118

 

Subsequent growth and development. Celosia. Time to ﬂower decreased (by 10
days) as DLI during the plug stage increased from 4.1 to 14.2 mol-m'z-d'l (Fig. 4A).
Correspondingly, node number below the ﬁrst inﬂorescence decreased by 7 nodes as
initial DLI increased from 4.1 to 14.2 mol-m’Z-d" (Fig. 4B). Flower number at ﬁrst
ﬂower and dry weight decreased linearly (by z61% and z31% , respectively) as the
initial DLI increased within the range studied (Fig. 4C-D). Plant height at ﬂowering
also decreased linearly (from 22.2 to 18.7 cm) as initial DLI increased from 4.1 to 14.2
. mol-m‘zd‘1 (Fig. 4E).

Impatiens. The relationship between days to ﬂower after transplant and DLI was
quadratic; days to ﬂower decreased from 36 to a minimum of 2:24 days as the initial
DLI increased from 4.1 to ~12 mol-m‘Z-d‘1 (Fig. 5A). Additionally, node number below
the ﬁrst open ﬂower decreased linearly, from 7 to 4 (Fig. 5B). Flower number and
ﬂower size decreased linearly from 49 to 20 (Fig. 5C) and from 5 to 4.5 cm,
respectively (Table 3). As the initial DLI increased from 4.1 to 14.2 mol-m'z-d", dry
weight and height at ﬁrst ﬂower decreased linearly by 59% and 24% , respectively (Fig.
5D and E).

Salvia. Time to ﬂower decreased by 11 days as initial DLI increased from 4.1
to 14.2 mol-m‘Z-d'1 (Fig. 6A). Plants developed fewer nodes below the inﬂorescence
when plugs were grown under higher DLIs, decreasing from 6 to 4 (Fig. 6B).
Signiﬁcant linear relationships were also observed between initial DLI and ﬂower
number, ﬂower size, dry weight and height (Figure 6C to B, Table 3). As initial DLI

increased from 4.1 to 14.2 mol-m’Z-d", ﬂower number decreased from 2 to 1 and ﬂower

119

size decreased from 4.1 to 3.1 cm. Dry weight and height at ﬂowering decreased with
increasing DLI by 62% and 25% , respectively.

T agetes. Time to ﬂower decreased by only 4 days as initial DLI increased from
4.1 to zllmol-m'Z-d'l (Fig. 7A). Node number decreased very slightly (from 4.3 to
3.5) as initial DLI increased from 4.1 to 14.2 mol-m‘Z-d" (Fig. 7B). Flower number
was not affected by the initial DLI treatments (Fig. 7C). Flower size decreased slightly
(from 4.3 to 4.0 cm) as DLI decreased from 14.3 to 4.1 mol-m’z-d" (Table 3). Dry
weight decreased linearly as DLI increased (Fig. 7D). Height was quadratically related
to the initial DLI (Fig. 7E).

Viola. Time to ﬂower was hastened by 12 days as initial DLI increased from
4.1 to 2:11 mol-m'Z-d‘l (Fig. 8A). Flower number and dry weight decreased lineme
from 11 to 7 and by 26%, respectively, as initial DLI increased from 4.1 to 14.2
mol-m‘z-d'l (Fig. 8C and 8D). Node number, ﬂower size, and height at ﬂowering were
not signiﬁcantly affected by the initial DLI treatments (Fig. SB, 8E, Table 4).
Discussion

Although temperature is often considered to be the main environmental factor
inﬂuencing plant rate of development, our study shows some inﬂuence of DLI.
Average node number at transplant increased with increasing DLI, indicating increased
developmental rates during the plug stage for all species, except for Salvia, where DLI
had no effect. Node number below the ﬁrst open ﬂower in Salvia, Celosia, and

Impatiens decreased as initial DLI increased, indicating higher rates of ﬂoral

120

development. This indicates that seedlings provided with a high DLI during the plug
stage will ﬂower earlier and develop fewer nodes before ﬂower initiation.

Previous studies on DLI during the plug stage have shown a hastening of
ﬂowering with an increase in DLI. Begonia semperﬂorens seedlings, provided with
continuous supplemental light at 233 umol-m‘Z-s" delivered 15 to 25 days after
germination showed a decrease in days to transplant and days to ﬂower by z 4 days as '
compared with plants under 13 umol-m‘Z-d". However, these results could have been
confounded with an increase in temperature (up to 4 °C) under the higher light intensity
(Graper and Healy, 1990). Flowering of Petunia xhybrida seedlings grown under
higher DLIs was accelerated by z14 days (Graper et al. , 1990). In our study, DLI
treatments increasing from 4.1 to 14.2 mol-m"2-d'l decreased subsequent time to ﬂower
in all species, but the magnitude varied among the plants tested (Fig. 4-8A). T agetes,
Celosia, Impatiens, and Salvia ﬂowering was accelerated 19%, 24%, 33% , and 41%,
respectively, as initial DLI treatments increased from 4.1 to 14.2 mol-m'z-d". Viola
ﬂowering was hastened by 28% as DLI increased from 4.1 to 11.5 mol-m‘Z-d" .. Most of
the observed differences in time to ﬂower can be attributed to DLI, as actual
temperatures were very similar among DLI treatments (S 1°C).

High quality plugs are those that have a large dry mass per node (i.e. thick
stems) and are relatively compact, since limited size and plug strength are important for
shipping and ease of transplanting. Using this deﬁnition for plant quality, at the time of
transplant, the quality of all species increased as average DLI increased (Fig. lA—E).

Average dry weight per average node number continued to increase linearly as initial

121

 

DLI increased from 4.1 to 14.2 mol-m‘Z-d" for all species, except for Salvia. Salvia
continued to increase until it reached a maximum under z12 mol-m'z-d", which may be
a saturating DLI for photosynthesis at ambient CO2 concentrations and at 21 °C (Fig.
1C). Additionally, increasing DLI decreased height at transplant in Impatiens and
Salvia, resulting in a more compact plug. Statistically DLI was quadratically related to
height of Celosia and T agetes, but these relationships were determined to be
horticulturally insigniﬁcant. Thus, this data indicates that supplemental lighting used to
increase DLI would increase plug quality and accelerate ﬂowering, at least in the range
of DLIs studied.

Flower number at ﬂowering in all species decreased as the initial DLI increased,
except for T agetes, in which initial DLI and ﬂower number had no signiﬁcant
relationship (Fig. 4-8C). Because plants grown under lower initial DLI treatments took
longer to ﬂower, the plants had a longer duration to harvest light in the subsequent
environment. Thus, plants had a longer time to photosynthesize and produce more
ﬂowers. There was no signiﬁcant relationship between initial DLI and ﬂower size in
Viola, but signiﬁcant relationships were observed in Impatiens, Salvia, and T agetes.

Dry weight at ﬂowering was linearly related to DLI in all species; with
decreasing initial DLI, dry weight at ﬂowering increased. This also may be explained
by the longer duration that plants were in the common environment due to delayed
ﬂowering. This ﬁnding posed the question of whether the dry weight gain per day to
ﬂower was related to the initial DLI treatment. Upon further inspection, decreasing

linear trends were observed in Celosia, Impatiens, and Salvia (Fig. 9), indicating that

122

 

as DLI increased during the plug stage, dry weight gain per day to ﬂower decreased.
This indicates that plants may allocate more energy into ﬂowers if initially exposed to
higher DLIs. Alternatively, plants may have had larger leaves when grown under a
low DLI initially, and thus were able to capture more radiation than plants grown under
a higher DLI. We did not measure leaf area, so further research is needed to support
this hypothesis.

Plant height at ﬂowering decreased linearly with increasing initial DLI in
Celosia, Impatiens, and Salvia. Much of this height difference could be attributed to a
corresponding linear decrease in node number. Height differences were not as highly
correlated in T agetes and were not signiﬁcant in Viola. Corresponding node number
differences were very small in T agetes and not signiﬁcant in Viola.

This study quantiﬁes the consequences of growing seedlings under a range of
DLIs. Although ﬁnal ﬂower number, ﬂower size, dry weight were greater under lower
initial DLI, ﬂowering was hastened as DLI increased. Future research to determine
how exposure to high DLI at different stages of seedling development inﬂuence initial

quality and subsequent ﬂowering would be of merit.

123

Literature Cited

Adams, S.R., S. Pearson, and P. Hadley. 1997. The effects of temperature,
photoperiod and light integral on the time to ﬂowering of pansy cv. Universal Violet
(Viola xwittrockiana Gams.). Ann. Bot. 80(1):107-112.

Armitage, A.M. and H.Y. Wetzstein. 1984. Inﬂuence of light intensity on ﬂower
initiation and differentiation in hybrid geranium. HortScience 19(1): 114-116.

Carpenter, W.J. and RC. Rodriguez. 1971. Earlier ﬂowering of geranium ‘Carefree
Scarlet’ by high intensity supplemental light treatment. HortScience 6(3):206-207.

Dansereau, B., Y. Zhang, and S. Gagnon. 1998. Stock and snapdragon as inﬂuenced
by greenhouse covering materials and supplemental light. HortScience 33(4):668-671.

 

Dressen, DR. and R.W. Langhans. 1992. Temperature effects on growth of impatiens
plug seedlings in controlled environments. J. Amer. Soc. Hort. Sci 117(2):209-215.

Erickson, V.A., A. Armitage, W.H. Carlson, and RM. Miranda. 1981. The effect of
cumulative photsynthetically active radiation on the growth and ﬂowering of the
seedling geranium, Pelargonium xhortorum Bailey. HortScience 15(6):815-817.

Graper, D. F. and W. Healy. 1990. Synergistic acceleration of Begonia sempetﬂorens
development using supplemental irradiance and soil heating. Acta Hortic. 272:255-259.

Graper, DP. and W. Healy. 1991. High pressure sodium irradiation and infrared
radiation accelerate Petunia seedling growth. J. Amer. Soc. Hort. Sci. 116(3):435-438.

Graper, D.F., W. Healy, and D. Lang. 1990. Supplemental irradiance control of
petunia seedling growth at speciﬁc stages of development. Acta Hortic. 272:153-157.

Kaczperski, M.P., W.H. Carlson, and MG. Karlsson. 1991. Growth and development
of Petunia xhybrida as a function of temperature and irradiance. J. Amer. Soc. Hort.
Sci. 116(2):232-237.

Lieth, J H R.H. Merritt, and HG Kohl, Jr. 1991. Crop productivity of petunia in
relation to photosynthetically active radiation and air temperature. J. Amer. Soc. Hort.
Sci. 116(4):623-626.

Niu, G., R.D. Heins, A.C. Cameron, and W.H. Carlson. 2001a. Temperature and
daily light integral inﬂuence plant quality and ﬂower development of Campanula
carpatica ‘Blue Clips’, ‘Deep Blue Clips’, and Campanula ‘Birch Hybrid’.
HortScience. 36(4):664-668.

124

Niu, G., R.D. Heins, A.C. Cameron, and W.H. Carlson. 2001b. Day and night
temperatures, daily light integral, and CO2 enrichment affect growth and ﬂower
development of Campanula carpatica ‘Blue Clips’. Scientia. Hortic. 87:93—105.

White, J .W. and U. Warrington. 1984. Growth and development responses of

geranium to temperature, light integral, C02, and chlormequat. J. Amer. Soc. Hort.
Sci. 109(5):728-735.

125

 

Table 1. Actual environmental conditions inside growth chambers with three daily light
integral (DLI) treatments. LL=low light, ML= moderate light, HL= high light,
VPD = vapor pressure deﬁcit, R= replication.

 

 

 

Average Average air Average
DLI temperature VPD
R Treatment (mol- m’z- d") °C Average shoot-tip temperature °C (kPa)
Salvia Impatiens Celosia Tagetes

1 LL 4.5 21.0 21.1 21.7 21.5 20.5 0.6
ML 7.2 21.4 21.6 21.9 21.6 21.2 0.6
HL 14.2 21.0 21.3 21.6 21.4 20.7 0.6
2 LL 4.1 20.8 21.6 20.8 21.5 20.6 0.7
ML 7.1 21.4 21.5 21.9 21.7 21.3 0.6
HL 12.3 21.4 21.4 21.6 21.1 20.6 0.6

 

Table 2. Comparison of canopy and air temperatures (°C) during a 24-h period in
growth chambers.

 

 

DLI
(mol- m‘z- d") Salvia Impatiens Celosia Tagetes Viola
canopy air canopy air canopy air canopy air canopy arr
4.1 22.7 21.1 22.7 21.4 22.3 21.0 21.1 20.7 21.6 21.0
7.1 22.0 21.4 22.6 21.5 21.9 21.6 20.9 21.3 21.4 21.6
12.3 21.9 20.9 22.5 21.0 22.0 21.0 20.7 20.8 21.9 21.0

 

126

 

Table 3. The effect of daily light integral (DLI) during the plug stage on node number

at time of transplant (n= 16) and on subsequent ﬂower size.
Average DLI

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Species (mol—m'Z-day“) Average node number Average ﬂower size (cm)
Celosia 4-1 4.3 --
4.5 4.6 --
7.1 4.9 --
7.2 5.3 ~—
12.3 5.0 --
14.2 5.2 --
Signiﬁcance *"* '-
P Linear In”
P 0mm;— *III
Impatiens 4.1 4.0 5.0
4.5 4.7 4.8
7.1 5.1 4.6
7.2 5.5 4.6
12.3 4.9 4.2
_ 14.2 5.7 4.5
Signiﬁcance *** "*
P um, "no: "at
P Quadratic y” “r
Salvia 4.1 2.9 4.1
4.5 3 4.0
7.1 3 4.1
7.2 3 3.4
12.3 3 3.8
14.2 3 3.]
Signiﬁcance N5 "**
P Um NS t*#
P Quadratic NS NS
Tagetes 4.1 2.8 4.0
4.5 3.1 4.0
7.1 3.4 4.1
7.2 4 O 4.4
12.3 3.1 4.3
14.2 3.8 4.3
Signiﬁcance **" **"
P Linc" nun unt-
P Quadratic NS "
Viola 4.1 3.9 3.1
4.5 3.8 3.0
7.1 4.6 3.0
7.2 5.1 3.2
12.3 5.3 2.9
14.2 5.6 3.1
Signiﬁcance NS
P Linear *1" NS
P Mic **$ NS

 

 

NS, **.*** Nonsigniﬁcant or signiﬁcant at P S 0.01, or 0.001 respectively.
--, Data not recorded.

127

 

Figure 1. Relationships between daily light integral and average dry weight per average
node number as observed in Celosia, Impatiens, Salvia, T agetes, and Viola at time of
seedling transplant. Each symbol represents the averages of 16 plants. Equations for

regression lines are presented with corresponding r2 values.

128

 

Average dry weight (g)/average node number

0.008
0.007
0.006

0.005 <~

0. 004

0.003 ‘-

0. 002

0.007 ~

0.006 <-

0.005 <~

0.004

0.003

0.014 «
0.012 <-
0.010 ~~

0.008

0. 006 ~~

0.004
0.018
0.016

0.014 ..
0.012 -»

0.010
0.008

0. 006 ..

0. 004

0.012 <~

0.010
0.008
0.006
0.004
0.002

 

1»

1r

Celosia

 

 

,. r2 = 0.91
y = 0.0028 + 0.0004x

A A

 

4
I

I Y r

 

R2= 0.91
y = -0.0011 + 0.0024x- 0.0001x2

 

.0.

r

T agetes

   

r2= 0.93
‘ y= 0.0021+ 0.0012x

 

'1’
1b

uh-

1.

 

f T 1'

Viola

 
    
  

r2: 0.91
o y= 0.0018+ 0.0006x

 

 

0

2 4 6 8 10 12 14

Daily light integral (mol m'2 d'l)

129

16

 

Figure 2. Relationship between daily light integral and average height (cm) as observed
in Celosia, Impatiens, Salvia, and Tagetes at time of transplant. L= linear and Q:
quadratic. NS, *,*** Nonsigniﬁcant or signiﬁcant at P s 0.05 or 0.001, respectively.

Equations for regression lines are presented with corresponding r2 values.

130

 

Height (cm)

4.0

. 2_

3.5 «Celosra r — 0.12,
3.0 ‘1' § .1
2.5 .. W .
2.0 ..
1.5 «~ N5 - _ 2‘

L Q y— 218+ l.07x-0.005x
10 .L e f I 4 : :

I atiens 2_

3.5 T "W 1' _ 0.71 ‘
30 0. k ‘
2.5 .. I .
2.0 .. ’ 2.

L"'q'" y= 4.12-0.28x + .011x
]5 t 4. ¢ 4 ¢ ¢ 4
4.5 +Salvia r2: 0 80.
4.0 .. I <
3.5 <— <
:2“ . ‘
o ‘h I .
2.0 ~- -
1.5 ._L..-Q.-. y = 5.04 - 0.25x + 0.005x2+
10 ¢ ¢ 4 i f i i
4.5 "Tagetes r2: 0.40_
4.0 .. I l

I
3.5 " I I I j
3.0 <~
I

2’5 m- .0. .0. 2-
20 L Q y= 1.94+ 0.358x-0.0l7x

 

 

 

 

 

 

 

O 2 4 6 8 10 12 l4 16

Daily light integral (mol m'2 d")

131

 

 

I I I 7 I I I

 

 

 

 

100 ~- 1:] [:1 1:] a
. Impatiens E]
[:l Tagetes
80 -- -
1:]
O
60 -- -<
1:]

A
O
1
I
O
l

% visible bud at transplant

 

 

 

O
20 —— -
O
0 —- g. .
0 2 4 6 8 10 12 14 16

Daily light integral (mol in2 d")

Figure 3. The relationship between DLI and percent visible ﬂower bud at tranplant
in Impatiens and Tagetes.

132

 

Figure 4. The effect of daily light integral during the plug stage on subsequent days to
ﬂower, node number, ﬂower number, dry weight (g), and height (cm) in Celosia.
Error bars represent 95% conﬁdence intervals. L= linear and Q: quadratic. NS,***
N onsigniﬁcant or signiﬁcant at P 5 0.001, respectively. Equations for regression lines

are presented with corresponding r2 values

133

 

Days to flower

Node number

Dry weight (g) Flower number

Height (cm)

50

A y = 46.4 - 0.95x
45 “ r2= 078*
40 -
35 «~
30 "’ use
L
25 . t i t t t e
B y = 26.2 - 0.66x
25 -» r2= 0.81 .
20 r M i
15 «~ -
our NS
L Q
10 t : i i i t i
C y= 18.9-0.73x
20 “ 2— .
l r - 0.51
10 .. ¥
5 4 can NS é
L Q
0 e t s
1D y=5.1-0.l6X*
5 . 1 r2= 0.82.
4 0 N
3 ..
to. NS
"L Q
2 . . : . t . a
26 r E y = 23.2 - 0.27x .
24 .. r2= 0.50 ,
22 4 i
20 ..
18 _ on NS

16

 

 

 

 

 

 

 

 

 

2 4 6 8 10 12 l4 16

Daily light integral (mol m’2 d")

134

 

I.—

Figure 5. The effects of daily light integral during the plug stage on subsequent days to
ﬂower, node number, ﬂower number, dry weight (g), and height (cm) in Impatiens.
Error bars represent 95% conﬁdence intervals. L= linear and Q: quadratic. NS, *,
*** Nonsigniﬁcant or signiﬁcant at P S 0.05, 0.001, respectively. Equations for

regression lines are presented with corresponding r2 values

135

 

Node number Days ‘0 flower
N

Flower number
A
O

2.5 ..

Dry weight (g)

_o
u.

0.0

Height (cm)

-N
C: Ln :3

 

   

 

 

 
   

 

  

 

 

 

A y= 49.5 - 3.86x+ 0.15x2
b R2: 096‘
”‘1' un-
L Q
B y= 7.82-0.27x
r2= 0.90
Ln: QNS
.C ’y= 59.7-2.80x‘
1“ r2= 0.81 «
i
hit QNS é
D y= 2.7- 0.14x,
r2: 0.90
. § §
L QNS

 

 

0

2 4 6 8 10 12 l4 16
Daily light integral (mol 111‘2 day'l)

136

 

Figure 6. The effects of daily light integral during the plug stage on subsequent days to
ﬂower, node number, ﬂower number, dry weight (g), and height (cm) in Salvia. Error
bars represent 95% conﬁdence intervals. L: linear and Q= quadratic. NS, ***
Nonsigniﬁcant or signiﬁcant at P 5 0.001. Equations for regression lines are presented

with corresponding r2 values.

137

Flower number Node number Days to flower

Dry weight (g)

Height (cm)

35

A y = 32.9 - 0.94x
30 .. Q r = 0.85 .
25 ~
20 «-
Lt!!! QNS
15 i i i i t i i
7 B y = 6.9 - 0.20x ‘
2
= 0.94
6 r ~
5 -l
o
4 .
.0! NS
3 L :Q i i i 1 i i
C y = 2.7 -0.12x
4 ’ r2= 0.30 '
2 0 a
1 1 an NS } i
L Q
0 i t i : i i i
2.5 D y= 2.7-0.14x_
r = 0.94
2.0 -
1.5 -
1.0 u r
L ‘QNS
0.5 i i i i i l i
18 0 E I y= 18.4-0.50x,
i r = 0.55
16 «~ é ;
.4 .. i
12 .. i
10 1* Last QNS I
8 l i i i 1 . 1

 

 

  

 

 

 

 

 

 

2 4 6 8 10 12 l4 16
Daily light integral (mol m‘2 d'l)

138

Figure 7. The effects of daily light integral (DLI) during the plug stage on subsequent
days to ﬂower, node number, ﬂower number, dry weight (g), and height (cm) in

T agetes. Error bars represent 95% conﬁdence intervals. L= linear and Q= quadratic.
NS, *, **, *** Nonsigniﬁcant or signiﬁcant at P S 0.05, 0.01, or 0.001, respectively.

Equations for regression lines are presented with corresponding r2 values.

139

24 1 I T I I I I

 

 

 

 

 

 

 

 

 

3 A y= 26.8- 1.73x+ 0.073x2
E 22 “ R2: 0.91“
=1 20 -» *
Q
H
g 18 .. ‘
a
a 16 «-
14 i i i i i i i
5 w B y= 4.2-0.040x,
2': 2= 044
a r .
5 4 . ‘
ﬂ
8
e 3 ..
z t NS
L Q
2 I 1 1 r l I l
,_ 14 1 C
0
.D
g 12 .. i 1
‘ l
h {
0
B 10 «~
'2 NS NS
{in L Q
8 4 ¢ 4 i ¢ ¢ i
1.4 .. D y= 1.2-0.023»
3n r2= 0.30
,_ - i .
“En
£3 10 y f
t, 0.8
a t t
0.6 .. L ’ QNS
E y= 9.8+ 0.51x-0.026x2
13 ,_ R2= 0.50.
A
a i
U
v 12 ~~ 1
H
A
.2”
o 11
I ..
LNSQ
IO : t i t 'L ‘I i
0 2 4 6 8 10 12 14 16

Daily light integral (mol m'2 d’l)

140

 

Figure 8. The effects of daily light integral during the plug stage on subsequent days to
ﬂower, node number, ﬂower number, dry weight (g), and height (cm) in Viola. Error
bars represent 95% conﬁdence intervals. L= linear and Q: quadratic. NS, **, ***
Nonsigniﬁcant or signiﬁcant at P s 0.01 or 0.001, respectively. Equations for

regression lines are presented along corresponding r2 values.

141

 

50

Days to ﬂower

25

12 4-

]O 4.

Node number

Flower number

Dry weight (g)
'o

Height (cm)

 

45 ..
40 ..
35 ‘-

30 .. Lqumn

T

A y = 60.1 - 5.26x + 0.24x2
R2= 0.84‘

  

 

B

%i ll]

 

y= 12.8-0.40x .
r2= 0.21

G
I...
e—o—a

 

N
o

—
U!

.L A
v ﬁr

y= 2.1 -0.056x
r2: 0.58

   

 

p—u

O
I
Y

\D

 

 

 

 

2 4 6 8 10 12 l4 16

Daily light integral (mol m'2 d")

142

 

Figure 9. The effects of daily light integral during the plug stage on subsequent dry
weight gain per day to ﬂower in Celosia, Impatiens, Salvia, and T agetes. Error bars
represent 95% conﬁdence intervals. L= linear and Q: quadratic. NS, **, ***
Nonsigniﬁcant or signiﬁcant at P S 0.0] or 0.001, respectively. Equations for

regression lines are presented with corresponding r2 values.

143

eight gain per day to flower (g d!)

3

Dry

 

0.13
0.12 <
0.11 «L
0.10 <-

Celosia

0.09 ‘-
0.08 ‘-
0.07 «~

0.06
0.07

0.04 <-

0.03
0.02

0.08

0.06 <~

0.04 ~-

0.02
0.055

0.050
0.045

0.040 «-
0.035 0

0.030
0.060

0.055 -~
0.050 ~-
0.045 .
0.040 ‘-

0.035
0.030

y = 0:116;0.0018x‘
r2= 0.40

 

if Impatiens
0. 06 ..

0.05 <~

y = 0.072 -0.0026x 1
r2: 0.81 q

  

E

It.

 

.. Salvia

= 0.0959-0.0039x
r2: 0.92 ‘

   

Lit! QNS

A

 

«F

«i-

it

Tagmsy= 0031+ 0.0032x-0.002x2‘

R2= 0.38 .

E 1
u ‘

LNS Q

 

db

4|-

 

Viola 1

ll

LNS QNS

 

 

0

4 A
Y I

2 4 e a
Daily light integral (mol in"2 d

10 12 l4 l6
-1)

144

 

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