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TO AVOID FINES return on or More date due. ____________1 DATE DUE DATE DUE DATE DUE ASFP 1 I W» . 6% 3ng it 193:: 3' A MSU Is An Affirmative Action/Equal Opportunity Institution DEVELOPMENTAL AND TROPIC RESPONSES 0F ZEA MAIS (L.) AND Afififilflgfifilfi IflALlAflA (L.) HEYNH. TO TEMPERATURE CONDITIONS SIMULATING CONSERVATION TILLAGE BY Marie-Claude Fortin A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Crop and Soil Sciences 1989 0020757 ABSTRACT DEVELOPMENTAL AND TROPIC RESPONSES OF ZEA MAYS (L.) AND ARAQIDOPSIS IflALlAflA (L.) HEYNH. T0 TEMPERATURE CONDITIONS SIMULATING CONSERVATION TILLAGE By Marie-Claude Fortin Some aspects of Zea gays (L.) (corn) growth have been investigated under temperature conditions simulating the presence of crop residue covers. First, the effects of a straw mulch on the development and the agronomic characteristics (aboveground biomass, height, nitrogen concentration, nitrogen uptake, leaf area, grain and stover yields) of corn were measured in irrigated field experiments. Growth of residue-treated plants was similar or enhanced when compared to bare soil controls at similar stages of development. Subsequently, field experiments were designed to verify that the developmental delays observed with plants grown with residue covers could be accounted for by decreases in seed zone temperature under the residues. Time and thermal time between specific vegetative stages were measured for an oat straw mulch, an inert poplar mulch and a bare soil treatment. The results suggest that allelopathy may be an additional source of developmental delay and that its occurrence is weather-dependent. Finally, since mulch management practices can create horizontal temperature gradients and since corn root responses to such conditions are unknown, experiments under controlled conditions were designed to test if and how root direction of corn can be altered by thermal gradients perpendicular to the gravity vector. Primary roots of corn grown on agar plates exhibited positive thermotropism when exposed to gradients of 0.5 to 4.2 C cm*K In.order to characterize this phenomenon without the interaction of gravity, a wild-type and a gravitropism mutant of Arabiggpglg thaliaga Heynh. were used. The results show that the extent to which root thermotropism is exhibited varies widely with species, and in corn, is dependent on the gradient strength and the temperature of exposure. ACKNOWLEDGEMENTS I wish to express my sincere appreciation to Dr. F. J. Pierce and Dr. K. L. Poff, two outstanding advisors. Their confidence in my work, their friendship, and the time they invested in discussions and help for my various enterprises during these years made my Ph.(D) an enjoyable and challenging experience. I thank Brian Long for constant help throughout the springs, summers and falls of 1987, 1988 and 1989 and Therese Best for her obliging helpfulness during the course of my work in the PRL. Dr. Ritchie contributed to my understanding of maize physiology. The help of Dr. Erickson and the Nowlin Chair group was appreciated for providing the temperature reading equipment and the weather data. Thank you to Matt Zwiernik for being an excellent assistant in 1987; my regards to Becky Gray, for making the summer of 1988 more enjoyable. Credit is also due to Dan Knezek, Joy Wang, Bob Deatrick, John Ferguson and Bill Mohn who all made my work easier at one point or another. Finally, I wish to acknowledge Georges Fortin and Daniel Longtin, without whom all of this work would not have begun. iv TABLE OF CONTENTS List of Tables .................................................. vi List of Figures ............................................... viii Introduction ..................................................... 1 List of references ............................................. 3 Literature Review ................................................ 4 Modifications of the soil environment by crop residues ......... 4 Temperature and Zaa maya (L.) shoot growth ..................... 6 Temperature and Zea mays (L.) root growth ...................... 7 Arabidopsis thaliana (L.) Heynh. as a model system to understand plant physiology ................................... 10 List of References ............................................ 12 Chapter 1. Distinction between developmental and growth effects of crop residues on gaa mays (L.) ........... 17 Materials and Methods ............................. 19 Results and Discussion ............................ 21 List of References ................................ 41 Chapter 2. Timing and nature of Axaaa aativa (L.) straw mulch retardation of Zaa mayg (L.) vegetative development ......................................... 44 Materials and Methods ............................. 46 Results and Discussion ............................ 48 List of References ................................ 64 Chapter 3. Thermotropism by seedlings of zaa mays (L.) and Agaaigaaaia thaliana (L.) Heynh ..................... 66 Materials and Methods ............................. 68 Results and Discussion ............................ 72 List of References ................................ 86 Conclusions ..................................................... 88 LIST OF TABLES Table 1.1. Number of days (after emergence) to reach various developmental stages (D.S.) and grain water content at harvest for corn grown on bare and residue-covered soil ......... 31 Table 1.2. Total precipitation (rainfall plus irrigation), solar radiation, maximum daily air temperature, maximum daily soil temperature during various developmental stages (D.S.) of corn in 1987 and 1988 ........................................ 32 Table 1.3. Height (leaves extended) of corn grown on bare and residue-covered soil from emergence to silking .................. 33 Table 1.4. 1988 fourth, fifth and sixth leaf areas at V6, leaf area index (LAI) at R3 and 1987 and 1988 stover yield, grain yield and grain to stover ratio of corn grown on bare and residue-covered soil ............................................ 34 Table 2.1. Average daily maximum and minimum seed zone temperature from the day of mulch application (LTE2) to V6 ...... 57 Table 2.2. Average daily maximum seed zone temperature for various periods of development for a bare soil and mulch treatments applied at LTE2 or V4 ................................ 57 Table 2.3. Seed zone thermal time for the LTE2-V6 period and air temperature-based thermal time for the V6-V12 development interval for a bare treatment and an oat straw mulch and poplar excelsior mulch treatments applied at LTE2 or V4 ................ 58 Table 2.4. Days required between various developmental stages for corn grown on bare soil and soil covered with oat straw mulch applied at V4 ............................................. 59 Table 3.1. Effect of a 4.2 C cm‘1 temperature gradient on root length, direction and wiggliness of a wild-type (WT) and gravitropism mutant (GM) of Arabidopaia thaliana (L.) Heynh ..... 81 Table 3.2. Effect of germination temperature on root length, direction and wiggliness of a wild-type (WT) and gravitropism mutant (GM) of Arabidopaig thaliana (L.) Heynh .................. 81 vi Table 3.3. Effect of a 4.2 C cmfi-temperature gradient on shoot length, direction and wiggliness of a wild-type (WT) and gravitropism mutant (GM) of Arabidopais thaliana (L.) Heynh ..... 82 Table 3.4. Effect of germination temperature on shoot length, direction and wiggliness of a wild-type (WT) and gravitropism mutant (GM) of Arabidopsia thaliana (L.)Heynh ................... 82 vii LIST OF FIGURES Figure 1.1. Daily minimum and maximum soil temperature at the 2.5 cm depth from emergence to V6, in 1988 at the Michigan State University Research Farm, East Lansing, MI ................ 35 Figure 1.2. Dry weight of corn aboveground biomass at various stages of development in 1987 and 1988 .......................... 36 Figure 1.3. Dry weight of corn aboveground biomass at various dates during the vegetative period until 75% silking in 1988....37 Figure 1.4. Whole plant N concentration (A) and N uptake (B) at development stages V3, V6, V9, V12 and R1 in 1988 ............... 38 Figure 1.5. Whole plant N concentration at various dates during the vegetative period until 75% silking (A), and nitrogen uptake until V12 (B) in 1988 ........................................... 39 Figure 1.6. Corn height (leaves extended) at various dates and as a function of increasing leaf ligule number during the vegetative period in 1988 ....................................... 40 Figure 2.1. Daily average air temperature and rainfall from planting to the date all treatments reached V12 at the Michigan State University Research Farm, East Lansing, MI ................ 60 Figure 2.2. Seed zone temperature degree-day and air temperature degree-day accumulation from the day of mulch application (LTE2) to the day all plots reached V6 ............. 61 Figure 2.3. Additional number of days required by corn grown with an oat straw mulch and a poplar excelsior mulch to reach some vegetative developmental stages as compared to a bare soil treatment ....................................................... 62 Figure 2.4. Observed thermal time to V3, V4, V5 and V6 versus predicted thermal time from an adaptation of a Ceres-Maize phenology equation .............................................. 63 Figure 3.1. Diagram of the angle of deviation (6) of a corn primary root curving after the transfer of the seedling to a thermogradient plate. The positions of the root tip at the time of transfer and at the end of the experiment are marked .......................................................... 83 viii Figure 3.2. Angle of deviation of the primary root of corn exposed to various temperatures within four gradients ........... 84 Figure 3.3. Elongation growth of corn primary roots grown for 24 hours in darkness in insulated aluminum plates at constant temperatures .................................................... 85 Figure 3.4. Angle of deviation of the primary root of corn exposed to 14.7 C and 21 C within four gradients ................ 85 ix INTRODUCTION The no-tillage and conservation tillage cropping methods were developed in the Mid-West for the prevention of land degradation from soil, water and wind erosion associated with the traditional ways of preparing soil for row crops. Adoption of these systems relied mostly on the fact that conservation tillage also provides economy of labor and energy, and reduces evapotranspiration. Along with these benefits come some important disadvantages such as problems with weed control and soil temperature (Phillips and Phillips, 1984). In the northern agricultural regions of this continent, the consequences of altered soil thermal regimes have been extensively studied because of their impact on crop plants, particularly Zaa maya (L.). The single most important factor modifying soil temperature regimes in conservation tillage environments is the amount of mulch left on the soil surface (Potter et al., 1985). Crop residues modify the radiant energy balance, resulting in the following effects: soil temperature under the residues can be lower than under a bare soil (Gupta et al., 1983); the amplitude of' diurnal temperature variations is reduced, decreasing the vertical gradients through the soil profile (Van Doren and Allmaras, 1978); and horizontal temperature gradients are created with systems that leave mulch materials in bands between the row or over the row (Allmaras and Nelson, 1971). This work attempts to develop an understanding of corn growth associated with some of these modifications of soil temperature induced by conservation tillage. The first study examines how some of the agronomic characteristics of corn grown with a residue cover compare with those of corn grown without residue cover when developmental differences are taken into account. The second study quantifies the extent to which developmental delays can be attributed to soil temperature. Finally, the third study explores if and how corn roots respond to horizontal temperature gradients. LIST OF REFERENCES Allmaras, R. R. and W. W. Nelson. 1971. Corn (Zaa maya L.) root configuration as influenced by some row-interrow variants of tillage and straw mulch management. Soil Sci. Soc. Am. Proc. 35:947-980. Gupta, S. C., W. E. Larson, and D. R. Linden. 1983. Tillage and surface residue effects on soil upper boundary temperature. Soil Sci. Soc. Am. J. 47:1212-1218. Phillips, R. E. and S. H. Phillips. 1984. No-tillage agriculture. Principles and practices. Van Nostrand Reinhold Co, N.Y. 306 p. Potter, K. N., R. M. Cruse, and R. Horton. 1985. Tillage effects on soil thermal properties. Soil Sci. Soc. Am. J. 49:968-973. Van Doren, D. M. and R. R. Allmaras. 1978. Effect of residue management practices on the soil physical environment, microclimate, and plant growth. p. 49-83. In Oschwald, W. R. (ed.) Crop Residue Management Systems. ASA Spec. Publ. 31. ASA, CSSA, SSSA, Madison, WI. LITERATURE REVIEW MODIFICATION QF THE SOIL ENVIRONMENT BY CROP RESIDUES The soil temperature of residue-covered fields is lower than that of bare soil surfaces (Willis et al., 1957; van Wijk et al., 1959; Burrows and Larson, 1962; Moody et al., 1963; Lal, 1974; Van Doren and Allmaras, 1978; Wierenga et al., 1982). During the day, crop residues cause a substantial decrease in temperature down to at least 10 cm, while at night the soil temperature is close to that of bare soils (Unger, 1978). This thermal regime results primarily from two different physical effects: higher reflectance or albedo of residues (Baumgardner et al., 1985) and insulation from layered air pockets trapped in the dead plant material (Gupta et al., 1981). .Only a few authors (Gupta et al., 1981; Gupta et al., 1984; Unger, 1988) have attempted to model soil temperature under residue covers because of the complicated nature of these soil temperature changes. Residue covers are not always layered uniformly across a field and their local placement can result in horizontal temperature gradients (Wierenga et al., 1982). This effect can be superimposed on other horizontal heat fluxes in the upper soil profile. These fluxes result from row cropping and can be far greater than the vertical gradients (Horton, 1984). They can result from the orientation of rows, especially in the case of raised beds or ridge tillage (Voorhees et al., 1981). They can also be a consequence of short range spatial variability of the soil physical conditions due to natural soil heterogeneity and tillage operations, mostly in the 0-14 cm depth. Thus, Cassel (1985) recommends that these considerations be taken in account in soil prediction models. The presence of residues on the soil surface results in other changes of physical, chemical or biological nature and they concern mostly soil water content, nutrient availability, phytotoxicity, and pest problems. In general, there is increased soil water content under mulched conditions (Moody et al., 1963; Kladivko et al., 1986) since residues contribute to water conservation by decreasing run-off and evaporation and increasing snow trapping (Unger et al., 1988). Higher soil water content also contributes to reduce soil temperatures and interacts with weed control, which in systems devoid of plowing, relies heavily on herbicides (Lindwall and Anderson, 1981). ReSidues can also be a source of phytotoxin release during rainfall or microbial breakdown. Toxicity varies with the nature and persistence of the residue (Guenzi et al., 1967; McCalla and Norstadt, 1974; Barnes and Putnam, 1983; Yakle and Cruse, 1984; Lodhi et al., 1987). Finally, residues contribute favorably to nutrient cycling, especially during the first season (Legg et al., 1971) although residues with low N content can reduce N availability in the first years and need to be accompanied by an appropriate nutrient management program. Among all these changes brought about by the presence of crop residues, the ones concerning soil temperature have the most direct effect on Zea mays (L.) (corn) growth during the early vegetative development. D ZEA MA 8 L SHOO ROWTH Most of the studies on corn shoot growth involving residue covers have been designed with some form of soil temperature monitering. As a result, there are several reports of positive correlations between the average soil temperatures resulting from residue applications (or conservation tillage) and corn growth and development characteristics such as early dry matter weight (van Wijk et al., 1959; Allmaras et al., 1964), leaf number to the sixth leaf stage (Swan et al., 1987), and relative growth rates (Al-Darby and Lowery, 1987). Thus, a slower growth rate or lower values of these various growth characteristics of the treatments involving residues have been attributed to decreased soil temperatures. Deviation from this general rule is usually interpreted as an interaction of soil water with soil temperature (Swan et al., 1987). All of these studies have assumed that lower soil temperatures under residues were the causal factor for observed growth differences with a bare control. There is little evidence to verify that this assumption is totally true. A few studies have related leaf number to an index integrating time and temperature (Al-Darby and Lowery, 1987; Swan et al., 1987). Research under controlled conditions has shown that temperature directly affects the shoot growth rate whether it is measured as time to emergence or xth leaf number (Walker, 1969; Hesketh et al., 1969; Alessi and Power, 1971; Swan et al., 1981; Tollenaar and Hunter, 1983), estimated as dry weight (Walker, 1969), measured as leaf elongation during a very short period of time (Barlow and Boersma, 1972), or monitered as leaf appearance or leaf initiation rates (Tollenaar et al., 1979; Warrington and Kanemasu, 1983). Despite this clear demonstration of the dependence of corn development on temperature, most agronomic research has only characterized corn growth under residue cover after specific periods of time on a day of year scale. As reviewed by Al-Darby and Lowery (1986), the effect of residues is almost invariable with the residue or conservation tillage treatments not faring as well as the bare or conventional tillage treatments, except for values of final grain or stover yields. The confounding of slower growth rates on such measurements is inevitable and has been avoided only in isolated cases in studies of dry weight and N upatke by Meisinger et a1. (1985) and Timmons et a1. (1986), respectively. Thus, there is a need to obtain more information on corn shoot growth once developmental differences due to residue covers are removed. YS OO GRO As with shoot growth, root growth of corn has been studied with respect to residue covers, mostly in relation to soil water and soil temperature. Both the practical aspects of root research on temperature effects under field conditions (Rykbost et al., 1975), and research under controlled conditions on elongation, growth, weight, nutrient uptake, and branching have generally been done at constant temperature (Beauchamp and Lathwell, 1967; Blacklow, 1972; Kleinedorst and Brouwer, 1972; Cooper, 1973; Brouwer, 1981; Mackay and Barber, 1984) with minima, maxima, optima temperatures and rates defined for specific temperatures. However, Allmaras and Nelson (1971) who have studied root weight and root growth indices as a function of soil water and temperature under natural conditions, have emphasized the importance of the influence of the row-interrow temperature differences in determining branching and elongation of corn roots. Unfortunately, there is little known about root responses to this inherent property of soils: temperature gradients. Beauchamp and Torrance (1969) have evaluated the temperature gradient that exists in young corn shoots exposed to different air and root temperatures but have not studied the roots. There are a few studies on the influence of temperature on the direction of root growth in corn. Mosher and Miller (1972) have observed the lack of response of corn roots to a temperature gradient applied opposite to or in the same direction as the gravity vector. Sheppard and Miller (1977) reported that the gravitropic response of corn seedlings is influenced by both a constant temperature of exposure and a diurnal cycle imposed on the whole seedling. Finally, Onderdonk and Ketcheson (1973) determined that it is the maximum of such cycles which influences the direction of root growth in corn. However, there is no report of how and if horizontal gradients affect root growth apart from old reports of thermotropism (change in direction of growth as a result of a thermal stimulus) (Hooker, 1914; Rose, 1929). This work is presently discredited because of rudimentary methods and conflicting results reported by different authors. Despite the lack of modern investigation on the subject, thermotropism is considered non-existent in roots. In recent sensory physiology reviews, roots were characterized as gravity-sensors only (Firn and Digby, 1980; Halstead and Dutcher, 1987). A notable exception is the review of Jackson and Barlow (1981) where the limited knowledge about the influence of temperature on the angle attained by the root as a result of gravitropism is recognized. One of the difficulties associated with studying the effect of temperature gradients on root direction is that temperature has a general effect on enzyme activities and most cellular processes (Voorhees et al., 1981). Therefore the different temperatures on the two sides of a root exposed to a thermal gradient could possibly induce "passive" changes in root direction without any "active" sensing. Another problem is the inescapable effect of gravity in determining at least in part, the direction of root growth. Since a direct approach to this problem resides in the use of gravity-insensitive mutants and since such mutants of corn are not available, a solution to this problem may reside in the use of another species as a model system. 10 S THALIANA L. HEYNH AS A MODE SYSTEM TO UNDERSTAND P 10 OGY Arabiaopsis thaliana (L.) Heyhn. is a small, self-fertilizing crucifer weed used in genetic work for over 40 years (Meyerowitz and Pruitt, 1985) which is becoming the "Drosophila" of the plant world. Because of its small size, its short life cycle of five weeks, easy light and nutrient requirements, and abundant seed set, it is easily and quickly grown to maturity in small pots. These conditions make it well suited for genetic work and several mutants have been isolated and characterized: phenotypic mutants used as genetic markers; biochemical mutants with lesions affecting respiration, photosynthesis, amino acid pathways, phytohormones, starch and lipid metabolism; and gravitropism and phototropism mutants with altered hypocotyl and root responses (Caspar et al., 1985; Estelle and Somerville, 1986; Khurana and Poff, 1989; Bullen et al., 1989; Meyerowitz, 1989). Several types of gravitropism mutants of Arabidopsis have been defined within the population of strains determined to have altered gravitropism (Bullen et al., 1989). These types have been classified on the basis of a 1-g induced curvature by rotating the plants on their side. "Random" strains have curvature frequency distribution histograms similar to that of wild-types grown on a clinostat (Bullen et al., 1989). On a clinostat, plants are continuously rotating and changing their perception of the gravity stimulus, and fail to orient their roots or shoots to a unilateral gravity vector (Volkmann and Sievers, 11 1979). Thus, these "random" mutant strains fail to detect the omnipresent l-g force and constitute a unique possibility for studying how root respond to environmental variables. They could permit a definite answer to the question of temperature gradients on root growth. LIST OF REFERENCES Al-Darby, A. M. and B. Lowery. 1986. Evaluation of corn growth and productivity with three conservation tillage systems. Agron. J. 78:901-907. Al-Darby, A. M. and B. Lowery. 1987. Seed-zone soil temperature and early corn growth with three conservation tillage systems. Soil Sci. Soc. Am. J. 51:768-774. Alessi, J. and J. F. Power. 1971. Corn emergence in relation to soil temperature and seeding depth. Agron. J. 63:717-719. Allmaras, R. R. and W. W. Nelson. 1971. Corn (Zea aaya L.) root configuration as influenced by some row-interrow variants of tillage and straw mulch management. Soil Sci. Soc. Am. Proc. 35:947-980. Allmaras, R. R., W. C. Burrows, and W. E. Larson. 1964. Early growth of corn as affected by soil temperature. Soil Sci. Soc. Proc. 28:271-275. Barlow, E. W. R. and L. Boersma. 1972. Growth response of corn to changes in root temperature and soil water suction measured with an LVDT. Crop Sci. 12:251-252. Barnes, J. P. and A. R. Putnam. 1983. Rye residues contribute weed suppression in no-tillage cropping systems. J. Chem. Ecol. 9:1045-1057. Baumgardner, M., L. F. Silva, L. L. Biehl, and E. R. Stoner. 1985. Reflectance properties of soils. Adv. Agron. 38:2-43. Beauchamp, E. G. and D. J. Lathwell. 1967. Root-zone temperature effects on the early development of maize. Plant Soil 26: 224-234. Beauchamp, E. G. and J. K. Torrance. 1969. Temperature gradients within young maize plant stalks as influenced by aerial and root zone temperatures. Plant Soil 30:241-251. Blacklow, W. M. 1972. Influence of temperature on germination and elongation of the radicle and shoot of corn (Zaa may; L.). Crop Sci. 12:647-650. 12 l3 Brouwer, R. 1981. Co-ordination of growth phenomena within a root system of intact maize plants. Plant Soil 63:65-72. Bullen, B. L., T. R. Best, M. Gregg, S. E. Barsel, and K. L. Poff. 1989. A direct screening procedure for gravitropism mutants of Arabiaaaaia thaliaaa (L.) Heynh. Submitted to Plant Cell Env. Burrows, W. C. and W. E. Larson. 1962. Effect of amount of mulch on soil temperature and early growth of corn. Agron. J. 54:19-23. Caspar, T., S. C. Huber, and C. Somerville. 1985. Alterations in growth, photosynthesis and respiration in a starchless mutant of Arabidopsis thaliana (L.) deficient in chloroplast phosphoglucomutase activity. Plant Physiol. 79:11-17. Cassel, D. K. 1985. 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J. 45:405-412. Halstead, T. W. and F. R. Dutcher. 1987. Plants in space. Ann. Rev. Plant Physiol. 38:317-345. Hesketh, J. D., S. S. Chase, and D. K. Nanda. 1969. Environmental and genetic modification of leaf number in maize, sorghum, and Hungarian millet. Crap Sci. 9:460-463. Hooker, J. D. J. 1914. Thermotropism in roots. Plant World 17:135-153. l4 Horton, R., O. Aguirre-Luna, and P. J. Wierenga. 1984. Observed and predicted two-dimensional soil temperature distributions under a row crop. Soil Sci. Soc. Am. J. 48:1147-1152. Jackson, M. B. and P. W. Barlow. 1981. Root geotropism and the role of growth regulators from the cap: a re-examination. Plant Cell Env. 4:107-123. Khurana, J. P. and K. L. Poff. 1989. Mutants of Araaiaaaaia thaliana with altered phototropism. Planta 178: 400-406. Kladivko, E. J., D. R. Griffith, and J. V. Mannering. 1986. Conservation tillage effects on soil properties and yield of corn and soya beans in Indiana. Soil Tillage Res. 8:277-287. Kleinedorst, A. and R. Brouwer. 1972. The effect of local cooling on growth and water content of plants. Neth. J. Agric. Sci. 20:203-217. Lal, R. 1974. No-tillage effects on soil properties and maize production in West Nigeria. Plant Soil 40:321-331. Legg, J. 0., F. W. Chichester, G. Stanford, and W. H. DeMar. 1971. Incorporation of lSN-tagged mineral nitrogen into stable forms of soil organic matter. Soil Sci. Soc Am. Proc. 35:273-276. Lindwall, C. W. and D. T. Anderson. 1981. Agronomic evaluation of minimum tillage systems for summer fallow in southern Alberta. Can. J. Plant Sci. 61:247-253. Lodhi, M. A. K., R. Bilal, and K. A. Malik. 1987. Allelopathy in agroecosystems: wheat phytotoxicity and its possible roles in crop rotation. J. Chem. Ecol. 13:1881-1891. Mackay, A. D. and S. A. Barber. 1984. Soil temperature effects on root growth and phosphorus uptake by corn. Soil Sci. Soc. Am. J. 48:818-823. McCalla, T. M. and F. A. Norstadt. 1974. Toxicity problems in mulch tillage. Agric. Env. 1:175-190. Meisinger, J. J., V. A. Bandel, G. Stanford, and J. O. Legg. 1985. Nitrogen utilization of corn under minimal tillage and moldboard plow tillage. I. Four-year results using labeled N fertilizer on an atlantic coastal plain soil. Agron. J. 77:602-611. Meyerowitz, E. M. 1989. Arabiaopaia, a useful weed. Cell 56:263-269. Meyerowitz, E. M. and R. E. Pruitt. 1985. Arabiaapa1a_§ha11ana and plant molecular genetics. Science 229:1214-1218. 15 Moody, J. E., J. N. J. Jones, and J. H. Lilland. 1963. Influence of straw mulch on soil moisture, soil temperature and the growth of corn. Soil Sci. Soc. Proc. 27:700-703. Mosher, P. N. and H. M. Miller. 1972. Influences of soil temperature on the geotropic response of corn roots (Zaa mays L.). Agron. J. 61:459-462. Onderdonk, J. J. and J. W. Ketcheson. 1973. Effect of soil temperature on direction of root growth. Plant Soil 39:177-186. Rose, M. 1929. La question des tropismes. Presses Universitaires de France, Paris. 469p. Rykbost, K. A., L. Boersma, H. J. Mack, and W. E. Schmisseur. 1975. Yield response to soil warming: agronomic crops. Agron. J. 67:733-738. Sheppard, S. C. and M. H. Miller. 1977. Temperature changes and the geotropic reaction of the radicle of Zaa maya L. Plant Soil 47:631-644. Swan, D., D. M. Brown, and M. C. Coligado. 1981. Leaf emergence rates of corn (Zea mays L.) as affected by temperature and photoperiod. Agric. Meteorol. 24:57-73. Swan, J. B., E. C. Schneider, J. F. Moncrief, and W. H. Paulson. 1987. Estimating corn growth, yield, and grain moisture from air growing degree-days and residue cover. Agron. J. 79:53-60. Timmons, D. R., T. M. Crosbie, R. M. Cruse, D. C. Erbach, and K. N. Potter. 1986. Effect of tillage and cornohybrids on N, P, and K uptake at different growth stages. Maydica 31:279-293. Tollenaar, M. and R. B. Hunter. 1983. A photoperiod and temperature sensitive period for leaf number in maize. Crop Sci. 23: 457-460. Tollenaar, M., T. B. Daynard, and R. B. Hunter. 1979. Effect of temperature on rate of leaf appearance and flowering date in maize. Crop Sci. 19:363-366. Unger, P. W. 1978. Staw mulch effects on soil temperature and sorghum germination and growth. Agron. J. 70:858-864. Unger, P. W. 1988. Residue management effects on soil temperature. Soil Sci. Soc. Am. J. 52:1777-1782. 16 Unger, P. W., G. W. Langdale, and R. I. Papendick. 1988. Role of crop residues - Improving water conservation and use. p. 69-100. In W.L. Hargrove (ed.) Cropping strategies for efficient use of water and nitrogen. ASA Spec. Publ. 51. ASA, CSSA, SSSA, Madison, WI. Van Doren, D. M. and R. R. Allmaras. 1978. Effect of residue management practices on the soil physical environment, microclimate, and plant growth. p. 49-83. In Oschwald, W. R. (ed.) Crop Residue Management Systems. ASA Spec. Publ. 31. ASA, CSSA, SSSA, Madison, WI. van Wijk, W. R., W. E. Larson, and W. C. Burrows. 1959. Soil temperature and the early growth of corn from mulched and unmulched soil. Soil Sci. Soc. Proc. 23:428-434. Voorhees, W. B., R. R. Allmaras, and C. E. Johnson. 1981. Alleviating temperature stress. p. 217-266. In G.F. Arkin and H.H. Taylor (eds.) Modifying the root environment to reduce crop stress. ASAE Monograph 4. ASAE, St-Joseph, MI. Walker, J. M. 1969. One-degree increments in soil temperatures affect maize seedling behavior. Soil Sci. Soc. Am. Proc. 33:729-736. Warrington, I. J. and E. T. Kanemasu. 1983. Corn growth response to temperature and photoperiod II. Leaf-initiation and leaf appearance rates. Agron. J. 75:755-761. Wierenga, W. 0., W. E. Larson, and D. Kirkham. 1982. Tillage effects on soil temperature and thermal conductivity. p. 69-90. In P.W. Unger and D.M. VanDoren, Jr. (eds.) Predicting tillage effects on soil physical properties and processes. ASA Spec. Publ. 44. ASA and SSSA, Madison, WI. Willis, W. 0., W. E. Larson, and D. Kirkham. 1957. Corn growth as affected by soil temperatures and mulch. Agron. J. 49:323-328. Wolkmann, D. and A. Sievers. 1979. Graviperception in multicellular organs. p.573-600. In W. Haupt and M.E. Feinleib (eds.) Physiology of movements. Encyclopedia of Plant Physiology New Series Vol.7. Springer-Verlag, NY. Yakle, G. A. and R. M. Cruse. 1984. Effects of fresh and decomposing corn plant residue extracts on corn seedlings development. Soil Sci. Soc. Am. J. 48:1143-1146. CHAPTER 1 DISTINCTION BETWEEN DEVELOPMENTAL AND GROWTH EFFECTS OF CROP RESIDUES ON ZEA MAYS (L.) Experiments comparing Zaa aaya (L.) (corn) production under residue-covered and bare soil conditions (Willis et al., 1957; Burrows and Larson, 1962; Moody et al., 1963) and under conservation and conventional tillage (Griffith et al., 1973; Mock and Erbach, 1977; Timmons et al., 1986; Al-Darby and Lowery, 1986, 1987) have reported lower soil temperatures, delayed emergence, shorter plants and lower aboveground dry weights during the vegetative period, different whole plant nitrogen concentrations, and delayed silking. In general, the results have been summarized as residue-induced slower development and depressed growth of corn, and have been attributed to lower soil temperatures. The effect of temperature on the development of corn has clearly been shown both in the field (Mederski and Jones, 1963; Watts, 1973; Swan et al., 1987), and under controlled conditions, from leaf initiation and/or appearance measurements (Beauchamp and Lathwell, 1967; Tollenaar et al., 1979; Warrington and Kanemasu, 1983) and number of days to tassel emergence observations (Bonaparte, 1975). Soil temperature effect on corn growth was 17 18 investigated by Walker (1969) who showed that shoot dry weight and total leaf length were well correlated, and had a similar soil temperature optimum which was different from that of leaf initiation rate. Beauchamp and Lathwell (1967) also reported different effects of soil temperature on leaf development and on plant dry weight for corn grown until the sixth leaf stage. These studies indicate that leaf initiation and leaf growth should be studied independently with respect to temperature. Since residue covers can have a dramatic effect on soil temperature (VanDoren and Allmaras, 1978), and therefore on leaf development rates, height and biomass measurements can become a function of the developmental stage early in the season. However, most tillage studies reporting plant height and aboveground biomass have measured growth parameters at rather arbitrary points in time with little consideration for developmental differences. Also, these studies often did not take emergence delays into account in the interpretation of later plant development measurements such as tasselling, silking or maturity dates. Therefore, there is a need in agronomic studies of tillage to distinguish between the effects of residues on growth (increase in size of an organ or a plant part) and the effects of residues on development (rate of progression through the life cycle), (Hall, 1950). The objective of this research was to study the effects of plant residues on growth and development of corn during the vegetative period, at selective reproductive stages, and on yield and grain water content at the end of the life cycle. This study 19 was designed to exclude the confounding effects of delayed emergence on later development stages and of development delay on growth characteristics, and minimized water deficit differences between treatments through irrigation. This paper demonstrates the importance of considering developmental effects when assessing growth and the impact of such an approach on the interpretation of corn performance data. MATERIALS AND METHODS Field experiments were conducted in 1987 and 1988 at the Michigan State University Research Farm, East Lansing, Michigan (42 42'N, 84 28'W), on a Conover loam (mixed, mesic, Udollic Ochraqualf) cropped to continuous no-till corn since 1984. Two treatments consisting of a bare no-till left uncovered or having 100% of the plots'surface covered with straw residues applied at emergence were arranged in a randomized complete block design with four replications. Corn residues from the previous year were removed prior to establishment of the treatments. Corn was planted at 64,500 plants had-on 7 May 1987 (hybrid 'Pioneer Brand 3737'), and on 11 May 1988 (hybrid 'Pioneer Brand 3744') on an adjacent site. Starter fertilizer was applied through the planter at a rate of 11-45-45 kg ha‘1 (N-P-K) and was followed by a broadcast N application of 168 kg ha”*as ammonium nitrate. In 1987, wheat (Triticum aestivum L.) "cv. Frankenmuth" and oat (Avena sativa L.) "cv. Heritage" straw was applied three days prior to 50% emergence at a rate of 5.6 Mg ha*lixtl987 . In 1988, oat straw 20 "cv. Heritage" was applied one day prior to 50% emergence at a rate of 4.9 Mg haflu In.l987, ten consecutive plants in each plot were marked at the beginning of the growing season and observed during vegetative growth for dates at which 50% of the plants reached V8, V12 and VT stages of development (Ritchie and Hanway, 1982). On these dates, ten plants per plot were harvested; they were washed, oven-dried to determine the aboveground biomass, and ground for Kjeldahl analysis of whole plant N concentration. In 1988, ten plants were marked for determination of the day when 50% of the plants reached each of V3 through V16, and 75% of the plants reached R1 (silking). Ten plants were harvested in each plot whenever a treatment reached V3, V6, V9, V12 and R1 stages; height (leaves extended) was measured as well as aboveground biomass and N concentration. In 1988, the leaf area of the fourth, fifth and sixth leaves of V6 plants and leaf area index at R3 (milking) were determined on ten plants per plot using an electronic leaf area meter. In both years, soil temperatures were measured hourly at the seeding depth (2.5 cm) in each treatment of one of the replicates. The temperature readings of four copper-constantan thermocouples connected in series to a data logger were recorded for each treatment. Air temperature, rainfall, irrigation and solar radiation were recorded on site. Overhead irrigation was supplied both years. Soil water potential was monitored regularly using tensiometers at 15 cm depth, and irrigation was applied whenever the soil water potential of a treatment reached -0.05 MPa. 21 Analyses of variance were performed and differences between means were tested using the least significant difference test (LSD) at an alpha level of 0.05. W The 1987 and 1988 growing seasons were both warm and relatively dry, especially 1988 with a total of 68.6 mm of rainfall from the day of planting to the day where all plots reached 75% silking. The average soil temperatures at the 2.5 cm seeding depth in 1988 were lower under the residue cover than under the bare soil. This was due to lower daily maxima (Figure 1.1), a finding consistent with reports by Willis et a1. (1957), Burrows and Larson (1962) and Moody et al. (1963). Periodic equipment failure in 1987 prevents plotting of the data on a continuous basis. Plant Development . Prior to the addition of straw residues, the bare soil and residue treatments had synchronized development until emergence since 50% emergence was reached on all plots 11 days after planting i.e. 18 May for 1987 and 22 May for 1988. In both years, the subsequent developmental stages were attained at dates significantly later for the residue treatment than for the bare treatment (Table 1.1). In 1987, 3.8, 2.7 and 4.5 more days were required to reach the V8, V12, and VT stages, respectively for an average of 3.7 days delay until tasselling. In 1988, the residue treatment was delayed 3.7 days by V3 and 7.4 days by V4, 22 maintaining an average of 7.7 days delay until silking (Table 1.1). The rate of corn development is determined primarily by temperature, more specifically of the shoot apical meristem (Beauchamp and Lathwell, 1967). It is known that the shoot apical meristem is strongly affected by soil temperatures while it remains under or at the surface of the soil (Beauchamp and Torrance, 1969; Watts, 1973) i.e. until the V6 stage (Ritchie and Hanway, 1982). Accordingly, the 1988 data (Table 1.1) indicate that the developmental delay was fully manifested by V4. The average soil temperature maxima recorded prior to V4 were 24.8 and 21.3 C for the bare and the residue treatments, respectively. The delayed plants did not catch up past the V6 stage, when the apical meristems of plants in both treatments were exposed to air temperatures. Swan et a1. (1987) made a similar observation with corn grown under two tillage systems and four levels of surface residue. Finally, the water content of the grain at harvest was significantly higher for the residue treatment in both years, an indication of delay in maturity (Table 1.1). Burrows and Larson (1962) reported emergence delays with corn residue treatments varying from 4.5 to 17.9 Mg haq-while Willis et a1. (1957) reported a 6-day delay at silking for a 5.6 Mg'haq-oat straw residue treatment compared to a bare soil control. Reduced tillage treatments have also been reported to be delayed at silking and/or maturity (Mock and Erbach, 1977; Timmons et a1. 1986; Al-Darby and Lowery, 1986; Swan et al. 1987). 23 In both years, the extent of the delay (Table 1.1), the straw material and its application rates varied. A mixture of wheat and oat straw was applied in 1987 at 5.6 Mg hafl-while oat straw was applied at 4.9 Mg had-in 1988. However, there was a clear retardation of development each year that cannot be attributed to delayed emergence since the residue was applied around 50% emergence. Therefore, an accurate assessment of crop residue effects on corn growth requires that comparison of growth parameters be made at similar developmental stages in order to remove apparent growth effects due to differences in development. The interpretation of results analyzed in this way must also take into account that with the residue treatment the developmental stages were delayed and therefore, attained under different weather conditions than the bare soil control. Aboveground biomass In 1987, there was no significant difference between the two treatments for dry weight of aboveground biomass when the plants were at V8, but the residue treatment had significantly more biomass than the bare treatment at V12 and VT (Figure 1.2). Table 1.2 shows no major difference by V12 in solar radiation or average daily maximum air temperature. By VT, the residue treatment had received 8 mm or 3.4% more precipitation than the bare treatment. Although the total amounts are nearly equal, their distribution between emergence and V12 was different (Table 1.2). In any case, the residue treatment did not affect adversely the dry weight of 24 corn in 1987 during the vegetative period from V8 to VT. The 1988 aboveground biomass data (Figure 1.2) include earlier samplings than in 1987. The differences between treatments were not significant at V6, V9, and V12. The residue treatment had significantly more biomass at V3 and less biomass at R1 than the bare control. It appears that in 1988, the aboveground dry weight accumulation of corn was not affected in a consistent manner by the residue treatment during the vegetative period. Table 1.2 shows that from V12 to R1, the residue plants received 39% less precipitation than the bare plants which may help explain the significant difference at R1. From emergence to V3, the residue treatment had 10% more precipitation, similar solar radiation and average daily maximum air temperature, and a lower average maximum soil temperature than the bare treatment (21 versus 25 C). Lower soil temperatures between emergence and V3 did not inhibit growth although the reasons for higher biomass in the residue treatment are unclear. Beauchamp and Lathwell (1967) showed that dry weights at stages V2 to V6 were higher at root zone temperatures lower than 25 C. This implies that the dry weight differences between treatments may have depended on early season soil temperature differences and later, at R1, when the shoot meristems were subjected to air temperature, on the differences in environment- developmental stage interaction brought about by dissimilar development rates. Very few reports of corn dry weights during the growing season have been presented on a developmental stage basis and these studies involve tillage rather than residues treatments. 25 Our results agree with those of Meisinger et a1. (1985) who measured corn dry weight at Vll-V12 and found no significant difference between minimum tillage and moldboard plow treatments. Timmons et a1. (1986) measured lower dry weight per unit area with no-till as compared to a fall plow system at V4 and R1, but the differences were attributed to unequal rates of emergence and percentages of emergence. Most of the previous research has presented biomass data either at one point in time or on a calendar time scale. The 1988 results of Figure 1.2 are presented on a calendar time scale in Figure 1.3. The aboveground biomass of the bare treatment is higher than the residue treatment throughout the vegetative period. However, Figure 1.2 indicates that these differences are developmental in nature. Finally, when one or both treatments attained the silking stage (last two samplings) (Figure 1.3), there was no significant difference between the two treatments. In this form, our results concur with the many reports in the literature on the effects of temperature, reduced tillage or residue cover depressing dry weights of corn during the vegetative period (van Wijk et al., 1959; Burrows and Larson, 1962; Mederski and Jones, 1963; Mock and Erbach, 1977; Al-Darby and Lowery, 1986), but leads to a conclusion completely different from that derived from Figure 1.2. 26 Whole plant N concentration and uptake In 1988, whole plant N concentration at V3, V6, V12, and R1 (Figure 1.4A) show a significant difference only at V3 when the bare treatment was higher than the residue treatment. However, the values of both treatments are above 3%, and within the sufficiency range. Timmons et a1. (1986) reported no consistent effect of tillage on N concentration for no-till and fall plow treatments at V4, V18, R1 and R6 (physiological maturity). However, Meisinger et a1. (1985) did find significantly lower N concentrations in no-till than on plowed corn at the V11-V12 stage in two of three years studied. On a calendar time scale, the bare treatment whole plant N concentrations were highest very early in the season, (Figure 1.5A). From then on, there was no significant difference between the treatments until the 38th day after emergence i.e. when the bare plants had 9 leaves and the residue-treated plants had 7 leaves. Later, the difference in development shows up as the plants with a greater number of leaves and older leaves (bare treatment) have a significantly lower N concentration. Moody et a1. (1963) also measured lower N in unmulched corn in the first part of the growing season. When both treatments have terminated leaf growth (last sampling), there is no more difference (Figure 1.5A), as reported by Burrows and Larson (1962). There is no significant difference in N uptake of the two treatments at V3, V6, V9 and V12 (Figure 1.48). On a calendar basis, these same data indicate that until both treatments reach 27 the 55th day after emergence, the residue treatment is significantly lower than the bare treatment at most sampling dates (Figure 1.5B). The residue treatment's consistently lower N uptake in the set of data plotted on a calendar time (Figure 1.58) is not evident in Figure 1.4B, and suggests that in our study, this effect is mostly development—related. These results agree with Meisinger et a1. (1985) who did not find N uptake differences between minimum tillage and conventional tillage at Vll-V12 unless no N was applied as fertilizer. However, Timmons et a1. (1986) in a similar tillage study did find differences in N uptake at V4 and V18, with a 179 kg haq-application of anhydrous ammonia before planting. Plant Height The plant height (leaves extended) of the residue treatment was significantly higher at V3 and V6, significantly lower at V12, and similar to the bare treatment at V9 and R1 (Table 1.3). On a calendar basis, the plants of the residue treatment were significantly smaller throughout most of the vegetative period (Table 1.3) as reported by Burrows and Larson (1962) and Moody et al. (1963), except very early in the season and when treatments are either at or past silking (last sampling). Again, the conclusions drawn from sampling on arbitrary dates implies depressed growth while Table 1.3 indicates that the faster developing plants (bare treatment) can be shorter than or similar in height to the residue- treated plants when compared at equal stages of development. Mock and Erbach (1977) gave an indication of such a tendancy when they 28 presented juvenile plant heights taken at a July date, along with leaf number, with the dry weights increasing with the leaf numbers. In our experiment, environmental conditions must account in part for the observed differences: from emergence to V6, a combination of lower soil temperatures and 36% more precipitation for the residue treatment produced taller plants than in the bare treatment (Table 1.2). From the aboveground biomass, height, and nitrogen concentration data presented above, it is clear that while the response curve over time of a parameter appears interesting, its interpretation needs to be coupled with data on development. One way to accomplish this is to plot the parameter as a function of time and leaf number. For example, the plant height data is presented in Figure 1.6 in such a form. From Figure 1.6 it can be seen that the height difference observed 55 days after emergence also corresponds to a three leaf difference in development - or that the V6 to V8 plants of the residue treatment were taller than the V6-V8 bare plants although delayed by six to seven days - or that in both treatments, a plant of ten collared leaves attained a height of 150 cm. Leaf Area Leaf area of the fourth, fifth and sixth leaf of V6 plants and leaf area index (LAI) of R3 plants are shown in Table 1.4. All differences were significant at V6 with higher leaf areas for the residue treatment. Recently, Al-Darby and Lowery (1987) reported 29 that in general, leaf area values of four tillage treatments ranked as the cumulative soil-based degree-days when measurements were made weekly during the vegetative stage. Their results suggest that measurements based on calendar days assess developmental differences. However, their results do not permit one to distinguish growth from developmental effects of tillage. The leaf area results at V6 (Table 1.4) agree with the dry weight and height data presented above that the growth of corn prior to V6 was more favorable with the residue treatment than with the bare treatment in 1988. At R3, when leaf growth was terminated, there was no significant leaf area index difference between treatments, a pattern similar to dry weights and heights. Stover and Grain Yields There was no significant differences in grain yield between treatments in both years (Table 1.4). This has been reported earlier with residue or tillage treatments (Willis et al., 1957; Moody et al., 1963; Griffith et al., 1973; Jones et al., 1968; Van Doren et al., 1976; Al-Darby and Lowery, 1986), except in experiments where plant density (Mock and Erbach, 1977) or drainage conditions (Griffith et al., 1973) or length of the growing season (Swan et al., 1987) were limiting. The stover yield varied with years in this study. There was no significant difference between treatments in 1988, but the residue treatment was significantly higher than the bare treatment in 1987 (Table 1.4). The grain to stover ratio varies accordingly, emphasizing again the fact that 30 overall vegetative growth of the corn plants with residues cover is not depressed. Jones et a1. (1968) came to a similar conclusion in a 6-year study comparing vegetative yields of no-tillage to those of conventional tillage. Under irrigated conditions, during a 2-year study, residue cover of a no-till soil produced significant differences in development of corn plants but no consistently significant differences in above-ground biomass from V6 during the rest of the vegetative stage and in grain yield at the end of the season, when compared to the bare control. In 1988, a higher frequency of sampling showed that there was a retardation of development and an enhancement of growth during the period when the apical meristem was below ground. Presentation of the 1988 biomass, N concentration and uptake, and height data on a calendar day basis rather than on a growth stage basis overlooked delayed development effects and can lead to opposite conclusions concerning the general growth of the plants. It is suggested that one must distinguish effects on development from those on growth in order to gain a better understanding of the crop's physiology in the complex ecosystem of a field situation. Moreover, accounting for growth stages also permits more precise inferences about the weather data and improves the interpretation of results. 31 .uuucuusuumv vocmuuuvcs we unnuo><++ ..~eo_. mazes: an. museums an anemone .<+ ~.~ ~.n oucuuouwmv .u>< n.~ o.» n.m N.~ N.o_ o.o n.o q.~ ~.m n.q ~.~ m.n mucououuma o.~ c.~ n.~ o._ m.o ~.~ «.m m.o o.o m.o . o.~ m.~ c.~ °.~ Anc.cv and ~.n~ ¢.oo ~.oo c.mo ~.en o.mc ~._m o.m~ ~.- n.¢_ ~.m~ n.oo ~.~¢ ~.~n scum-um m.- n.co ~.on m.on n.~e m.~m «.mw n.- w.c_ o.c_ m.o_ c.on o.ne e.nn «can IINI mama IINII Illlluaav Incl- .a e> e_> -> m> e> n> q> mm: e> -> m> aucueuuots soon: .m.= Loan: .m.a smote :mwuu mom" ~mm~ ucw> .—mom vmuo>oonmzvmmos use when so czouu :uou sew uao>uu£ an acuucou some: away» one A.m.cv +momcua ~oucoan_o>mp msomuu> coco» cu Aoucsuuoso nouucv mama no human: .—.~ u~nuh 32 ounnum~aauncoc « <\z <\z c.9n m.~n cn.m~ em.o~ ¢.e¢ ~.~n ->Ia> <\z <\z ~.~n m.~m -.n~ mm.o~ _.o~ o.o¢ m>lo> c.n~ s.m~ o.~n c.a~ co.m~ —¢.m~ ~.«q c.nu o>nn> ~.- ~.n~ ¢.- m.~m mm.o~ me.om o.~¢ o.mn n>|+xm coma <\z <\z ¢.o~ ~.on -.om mm.mm ¢.ao c.~o h>n-> (\z <\z e.- o.- ec.o~ oc.m~ °.- c.no ->Io> mammals usau.ae n.o~ m.- ac.- ac.- e.an. c.oo~ c>-.+:u soma osvmmuz when usvmaum whom msommom whom osvmaoz ouum a~a>uou=~ new» .m.a wtsucuumth ~mom mtzoatomsmu Mwm IszMwacm ummmw comuoummmuoum >_maa Eaemxux >_mun Ezemxcz wumto>< oweuu>< owoto>< .mma— can “can cm cuou mo A.m.av +mowcuu _aucwan—o>op msomtu> wsmtsv ousuuuoasou ~m0o >_muo Easmxus .ouaucuuaEuu uma »_mcv Easmxoe .comuemouu us—0m .Acomuammoum m:_a -uucmuuv comucumamuuua ~uuoh .~.~ epoch 33 .Anmaav asses: can omzuuma an vocmuov uo+ n.¢~ o.~n~ n.~¢~ ~.o~ c.c— c.~o~ ¢.o- o.n¢~ ~.nc~ ~.c~ ¢.- «.9. m.q w.e o.c m.m ~.cm_ v.-— n.co o.o~ c.~¢ ~.s~ ~.¢~ o.cm_ c.~o~ c.o~_ o.mm o.co m.wm m.~m mo co an we no an —M an q~ .— oocowonm gonna «use .wcmx.mm on mucowtmEm Esau ~m6m cmuo>cUnozsmmot act was: cc o.o_ q.w m.m m.~ c.~ Ano.cvnma c.~n~ o.o- ¢.-~ c.o~ ~.n~ «semen: ~.¢c~ o.qo_ c.0n— o.co m.- use: ~¢ m.> a> o> n> aucoeuuuuh +momaum _au:osmm~o>ua czotw shoe .0 Avov=~.xw mu>co_v Scams: .n.~ u—sqh 34 .A~ma~v auzcez can omsuqu as vocmuov uo+ mn.o ~m.¢ c~.~ mm.o n.~¢ m.n~ ~.m~ cq.c um.o n~.~ Anc.v am; on.~ c~.w na.n cm.n m.w~— ~.qo_ ~.~n c~.~ nn.o~ ~¢.o snow-oz ~m.~ cc.o no.e om.m o.om_ m.- n.~m No.~ a—.o_ -.o mean III~1¢£ wxllll IIIII!IIIIEII:~Eo Illlllll~ncg w: omen: v~um> v—omr ~ mucueuoouh uo>oum cmutu tu>0um mm .mo— ;.o Law. gum mom_ soc uu>0uw smote uu>oum on :mcuo o> o> o> cu :mauu £31. ! -5- -l», 1. $2 ._m0a vouo>cuuosvmuuu one atom no cash» :tcu .c amass tm>cam c. :mctw use c—mma cmuuu .v~omx uo>0uu mom. one swan vac +m¢ on A~ on mambo was. gamma van gamma .zu530u ama— .c.~ Ounah 35 O L h. ,uf a: TEMPERATURE (°c) Amt Bore, min T H Bore, max T Residue, min T H Residue, mox T k ##_L II I II I' r T Y o r...,...., ,...-,....,....r- 5 10 15 20 25 30 DAYS FROM EMERGENCE TO vs C) Figure 1.1. Daily minimum and maximum soil temperature at the 2.5 cm depth from emergence to V6, in 1988 at the Michigan State University Research Farm, East Lansing, MI. 36 muo<._.m 1.5510 b) Nu> a) H HL r H 393 :3 Ba. .omaa can head :« ucoamoHo>oo no momoum macauo> as mmmeo«n unsoumo>ono :uoo no anode: aha .~.H ousmam pm a.) Q> n> , _ a J...|-o 2.9.8 r I .o 0 19. w m 10m. nu m 100 6 m. D m... woo— (m 893 am; no: fiON— magnum I mg nu ow— 37 140+ e-e BARE ,f_ ’ LSD 7" 120.1 x4- (0.05) E ii 100‘ 3 80 E 5 [A I g 60~ 4* / I 3 3—1 I, >— 404 ,’ D: 2_, I O I 20~ ’ 14 , —,=‘f 0 r' l ' r”T r* r 0 10 20 60 70 DAYS AFTER EMERGENCE Figure 1.3. Dry weight of corn aboveground biomass at various dates during the vegetative period until 75% silking in 1988. 38 5.0 E (A) ID 95 4m:- 4.od “3" (“II 3.5- 3.0- I 2.5- 1 .5- L 1 .o , V3 vs vs v12 R1 GROWTH STAGES NITROGEN CONCENTRATION (x) 150 . CZZIBARE . - RESIDUE m (0.05) (B) L A .O O O l 50.. 1.5- ,... 1 [Li V3 V6 V9 V1 2 GROWTH STAGES NITROGEN UPTAKE (kg ha") Figure 1.4. Whole plant N concentration (A), and N uptake (B) at developmental stages V3, V6, V9, V12 and R1 in 1988. 39 NITROGEN CONCENTRATION (2) U ‘P (A) 2.5- 2.01 1.5. H RESIDUE b-t BARE 1'0 I T T l I T 0 10 20 30 40 50 60 70 200 < b-t BARE p 4 H RESIDUE lg : Ch 150- x i V «I U 1 X I I5 1OO-I % 1 2d 2 . E . . o 50- E 1" Z .I .I o I l l T r I 0 10 20 30 4O 50 60 7O DAYS AFTER EMERGENCE Figure 1.5. Whole plant N concentration at various dates during the vegetative period until 75% silking (A), and nitrogen uptake until V12 (B) in 1988. 40 .oomd :a cannon O>wuouomo> as» 95.26 .383: mama: wood unannouocu uo :Oauocsu a no one 23.3 2533' no Aooocouxo uo>o03 “£30: F30 .wé 0.33m mumzaz H.303 “Eu.— uozuommzw amt? m>o_ «9.: can as accumumcumm a .Oucouuoeo emu use. vacuom++ .Aaoaae sauce: an. «Manama as vocaaoe .< . a: «.6 o.o a: a: a: a: m: a: a: a: a: Amo.cv am; o.¢~ N.¢ o.o c.n o.o o.~_ m.m~ n.c~ m.n ~.~ N.¢ n.- use nn.c~ «.0 ~.~ n.c 6.0 o.~_ m.q~ m.o— m.c ~.n n.q N.- scam ~_>Io> m>uo> o>nm> n>Ie> ¢>In> n>I++~mbu ->Im> w>uo> o>na> n>nq> c>um> n>I++thA eucuaueouh mama woa~ teo> .c> us mum—nae £O_:E Jesus use sum: couo>ou ~m0a ace _mOm Ouch co czotw case to. +mcmc.m .cacoeao~o>ov asomue> ceoauon vuumsaou can: .e.~ u—ouh 60 ‘ . t 30' 1989 ; hm z-s . E I .0 I : :50 “J - :: :40 m :: . a ‘ :: :30 g , » E. ; LIJ 10-11 5. .3 5 320 g ‘ 53 5 5 A E—J ~H sags-10E >' ‘ 555 as s 5 v :’ O ....,....,....,....,....,....,..,,,,f,1,,' . O .1 <( .J o , E “J 30- 1988 : z 0 ‘ .. -60 '2 < _ a: E ‘ . : > 1 ' £50 < < : 2°‘ . : 4 :40 p ‘ ' . 530 1 : 1°- [-20 : ”-10 . B1 c o .0 om'émi'S'I's'E'O' 25 so 35 40 45 so 55 so 65 7o 75 so DAYS AFTER PLANTING Figure 2.1. Daily average air temperature and rainfall from planting to the date all treatments reached V12 at the Michigan State University Research Farm, East Lansing, MI 61 400 1989 , 320- " 240- A g . ‘0‘ 160+ I “J 4 DJ E 80-1 / H Poplar m / l—l Oct 8 ‘ e—a Bore w 0 ’ o—o Nr 2 400 I I l U I U I F- _, 1988 < d E LIJ .3201 I. F- < 2401 , 1604 1 80-J H Poplar H Oct 13-! Bore o—o Air CT 5 {013 23 23 3'0 3'5 DAYS AFTER LTE2 .Figure 2.2. Seed zone temperature degree-day and air temperature degree-day accumulation from the day of mulch application (LTE2) to the day all plots reached V6. 62 10 - out 1989 9- E Poplar 8‘ 7- v3 V4 vs vs v7 va— v12 - Oat 1988 9- E Poplar ADDITIONAL DAYS REQUIRED O l l l o- ._ _ ._ v3 V4 vs vs v7 va v12 GROWTH STAGES Figure 2.3. Additional number of days required by corn grown with an oat straw mulch and a poplar excelsior mulch to reach some vegetative developmental stages as compared to a bare soil treatment. 63 ‘ D Oat. 1989 300: - Oat. 1988 Q . 0 Bare. 1989 , g . 0 Bare, 1988 A I V6 | 1 A Poplar, 1989 BJJ 250‘ A Poplar, 1988 5 j A DA I V5 w ‘ Q 200- 8 1 *- ‘ V4 0 . m I B 150- m .I l q I 100 I r r r r r VT: r r 1— 1f r fl] T— I t , I r 100 150 200 250 .300 OBSERVED DEGREE-DAYS Figure 2.4. Observed thermal time to V3, V4, V5 and V6 versus predicted thermal time from an adaptation of a CERES-MAIZE phenology equation. LIST OF REFERENCES Al-Darby, A. M. and B. Lowery. 1987. Seed-zone soil temperature and early corn growth with three conservation tillage systems. Soil Sci. Soc. Am. J. 51:768-774. Alessi, J. and J. F. Power. 1971. Corn emergence in relation to soil temperature and seeding depth. Agron. J. 63:717-719. Barnes, J. P. and A. R. Putnam. 1983. Rye residues contribute weed suppression in no-tillage cropping systems. J. Chem. Ecol. 911045-1057. Beauchamp, E. G. and D. J. Lathwell. 1967. Root-zone temperature effects on the early development of maize. Plant Soil 26:224-234. Coelho, D. T. and R. F. Dale. 1980. An energy-crop growth variable and temperature function for predicting corn growth and development: planting to silking. Agron. J. 72:503-510. Griffith, D. R., J. V. Mannering, H. M. Galloway, S. D. Parsons, and C. B. Richey. 1973. Effect of eight tillage-planting systems on soil temperature, percent stand, plant growth, and yield of corn on fiVe Indiana soils. Agron. J. 65:321-326. Guenzi, W. D., T. M. McCalla, and F. A. Norstadt. 1967. Presence and persistence of phytotoxic substances in wheat, oat, corn, and sorghum residues. Agron. J. 59:163-165. Gupta, S. C., W. E. Larson, and R. R. Allmaras. 1984. Predicting soil temperature and soil heat flux under different tillage-surface residue conditions. Soil Sci. Soc. Am. J. 48:223-232. Jones, C. A. and J. R. Kiniry. 1986. CERES-MAIZE. A simulation model of maize growth and development. Texas A&M University Press, College Station. Lodhi, M. A. R., R. Bilal, and K. A. Malik. 1987. Allelopathy in agroecosystems: wheat phytotoxicity and its possible roles in crop rotation. J. Chem. Ecol. 13:1881-1891. McCalla, T. M. and F. A. Norstadt. 1974. Toxicity problems in mulch tillage. Agric. Env. 1:175-190. 64 65 Mock, J. J. and D. C. Erbach. 1977. Influence of conservation-tillage environments on growth and productivity of corn. Agron. J. 69:337-340. Muldoon, J. F., T. B. Daynard, B. Van Duinen, and M. Tollenaar. 1984. Comparisons among rates of appearance of leaf tips, collars, and leaf area in maize (Zea may: L.). Maydica 29:109-120. Ritchie, S. W. and J. J. Hanway. 1982. How a corn plant develops. Iowa Coop Ext Serv Spec Rep.48. Swan, J. B., E. C. Schneider, J. F. Moncrief, and W. H. Paulson. 1987. Estimating corn growth, yield, and grain moisture from air growing degree-days and residue cover. Agron. J. 79:53-60. Tollenaar, M., T. B. Daynard, and R. B. Hunter. 1979. Effect of temperature on rate of leaf appearance and flowering date in maize. Crop Sci. 19:363-366. Van Doren, D. M. and R. R. Allmaras. 1978. Effect of residue management practices on the soil physical environment, microclimate, and plant growth. p. 49-83. In Oschwald, W. R. (ed.) Crop Residue Management Systems. ASA Spec. Publ. 31. ASA, CSSA, and SSSA, Madison, WI. Walker, J. M. 1969. One-degree increments in soil temperatures affect maize seedling behavior. Soil Sci. Soc. Am. Proc. 33:729-736. Warrington, I. J. and E. T. KanemaSu. 1983. Corn growth response to temperature and photoperiod II. Leaf-initiation and leaf appearance rates. Agron. J. 75:755-761. CHAPTER 3 THERMOTROPISM BY SEEDLINGS OF ZEA MAXfi (L.) AND ARABIDOPSIS THALIANA (L.) HEYHN. Thermosensing is well documented in a variety of microorganisms such as Escherichia £21; (Maeda et al., 1976; Maeda and Imae, 1979), Dictyostelium discoideum (Poff and Skokut, 1977; Whitaker and Poff, 1980; Fontana and Poff, 1984) and in the nematode, Caenorhabditis elegans (Hedgecock and Russell, 1975). All these organisms exhibit thermotaxis or the ability to respond to thermal gradients by changing the direction of their movements. On the other hand, thermal gradient sensing in plants has not been well documented. Thermotropism, which is the directed orientation of a plant organ in response to a temperature gradient, was only reported in the late nineteeth century and early twentieth century literature. Hooker (1914) writes that Barthelemy executed the first experiments on root thermotropism with bulbs of hyacinth growing in water in 1884. In 1885, Wortmann presented data suggesting root thermotropism in Egzum lens, Piggy gagiygm and Zea may; (Hooker, 1914). In these experiments and those of several later workers, the methods and measurements were crude, and the results conflicting (Rose, 1929), discrediting this early sensory 66 67 physiology work. For example, while Klecker in 1891 cast doubts on the validity of the work of Barthelemy and of Wortmann on root thermotropism because of the lack of control of moisture in their experiments, he failed to demonstrate that moisture gradients could influence root direction. Later, Hooker (1914) attempted to disprove the existence of root thermotropism by showing the absence of response to thermal gradients when roots were grown in agar, free of exposure to moisture gradients. Meanwhile, Eckerson (1914) and Collander (1918) presented more evidence for, and Sierp in 1926, presented evidence against root thermotropism. Finally, Rose (1929) reviewing the literature did not take any position. In modern reviews of root sensory responses, the topic of root orientation in a thermal gradient is ignored because it is assumed that these early reports of thermotropism were due to artifacts. However, roots do have tropic responses to gravity and mechanical pressure (Feldman, 1984) and their curvature can be affected by unilateral application of certain cations (Hasenstein, 1988). Thermal effects on root growth, branching and metabolism at specific constant temperatures have been well studied subjects (Walker, 1970; Cooper, 1973). However, the question of root orientation within a temperature gradient is still unanswered mainly because most of the approaches to study the effects of temperature on roots consisted of subjecting the entire root system or the parts under study to constant controlled temperatures. However, compensation in one half of the root system for unfavourable temperatures in the other half has been demonstrated 68 using the split-root technique (Brouwer, 1981). Minorsky (1989) reviewed a series of experiments on cooling plants to temperature above their chilling injury threshold. Onderdonk and Ketcheson (1973) reported that the angle of corn root growth is influencedfby both constant and cyclic temperatures. Masher and Miller (1972) found no response when they studied the orientation of maize roots grown in an undefined thermal gradient applied opposite to or in the same direction as the gravity vector. Thus, the objectives of this work were to examine if 2;; may; (L.) primary roots respond to a thermal gradient applied- perpendicular to the gravity vector. Thermal gradients were found to influence the direction of root growth. Since this was the case, Arabidgpsis thaliana (L.) Heynh., ecotype Estland was chosen for further work because it offered the possibility of using mutants with gravity-insensitive roots and shoots to examine how thermal gradients interact with gravity in determining the direction of root growth. However, the Arabidopsis wild-type was found to have a small response to temperature gradients and the use of a gravitropism mutant did not enhance the response. Seeds of Agghiggpgis thaliana, ecotype Estland were sterilized and planted on 1% (w/v) agar plates supplemented with l mol.nr3IKN03 and 1% sucrose. The plates were sealed and incubated under light with the surface of the agar oriented vertically until 60% 69 germination i.e. 26 hours at 26 C or 30 hours at 16 C. The plates were then treated for 72 hours in darkness with the same vertical orientation in one of two ways: 1) transferred to a thermogradient plate set to a gradient of 4.2 C cur1 (Poff and Skokut, 1977), with the seeds in the petri dish at the position of 21 C within the gradient; 2) transferred to a similar plate at 21 C without a temperature gradient, as a control. In a second experiment, the MG-32 mutant strain of Arabidopsis thaliana, ecotype Estland with altered root and hypocotyl gravitropism (Bullen et al., 1989) was subsequently used as described above. An average of 700 plants were used in each experiment. Seeds of fig; gays, hybrid 'Pioneer 3744' were sterilized and soaked in sterile deionized water for 26 hours to stimulate germination. The seeds were then placed in the holes of thin perforated plexiglass strips embedded in 1% (w/v) agar plates supplemented with 1 mol m'3 KNOa and 1% sucrose. The plexiglass strips kept the corn seeds in place in the vertically oriented plates during the experiment. The plates were sealed and incubated under low light for 26 hours at 26 C, allowing the radicle to grow past the strip through the perforations to the agar. Then, the plates were screened for seedlings with radicles of 1 to 2 cm long. These plates were either placed on a thermal gradient or at constant temperature for 24 hours in darkness as described above for Arabidopsis. Further experiments with corn involved the same procedure as described above but with different gradient and temperatures of exposure within the gradient. A minimum of 60 70 plants was used in each individual experiment with corn. A solid aluminum block in which two channels were bored lengthwise was used to create a thermogradient plate by allowing each of two constant temperature water baths set at different temperatures to continuously circulate water within one side of the block (Poff and Skokut, 1977). The temperature gradient established across the block spanned the temperature from that of one bath to that of the other. A similar apparatus was used for the constant temperature control using only one circulating water bath channeling water to the two sides of the block, establishing a constant temperature across it. The aluminum block was insulated with a minimum of 9 cm of styrofoam and embedded in a commercial cooler. Three thermocouples were installed permanently on each aluminum block and read regularly using a programmable datalogger. The temperature on the surface of the agar was estimated through linear regression to the temperature on the aluminum block with a coefficient of determination of 0.99. The temperatures were maintained within 3 0.1 C for 72 hours and within 1 0.3 C for the entire period of the experiments. At the end of the treatments, the petri dishes were placed in a photographic enlarger and the shadowgraph of the seedlings was traced. The length and the final direction of the corn primary roots were measured. The final direction was determined relative to the direction after the 24-hour pre-treatment period i.e. the angle of deviation (9) from the original direction projection (Figure 3.1), using a protractor. Positive and negative angles indicate angles 71 towards the warm side and the cold side of the petri dish, respectively. The growth of Arabidopsis roots and hypocotyls was characterized with an angle of direction and a measure of curvature since the gravitropism mutant's shoots and roots are not only growing but curving in all directions. The direction of the Arabidopsis hypocotyls and roots was determined as an angle between 180° and -180° where 0° indicates a hypocotyl growing up or a root growing down in a perfect vertical orientation, and a negative angle indicates growth towards the cold side of the petri dishes while a positive angle indicates growth towards the warm side. In order to detect any change in the frequency of curvature of the hypocotyls or the roots of Arabidopsis, the "wiggliness" criterion was used. Wiggliness is defined as the the average rate of change of the slope of a curve (Rosenfeld, 1984). These data, as well as length were determined with a Vicom Image Analyzer computer programmed to digitize a video image of the hypocotyl or root shadowgraphs, break the image into segments of 10 pixels, record the coordinates of each segment and calculate the above mentioned parameters. Analyses of variance were performed to determine if the treatments were significantly different from each other. The treatments in the experiments with Arabidopsis were arranged in a split plot with the large experimental units as the germination temperatures in a completely randomized design and the small units as the gradient treatment and the control. The experiments with 72 corn included a gradient treatment and its control, arranged in a completely randomized design. W Zea mays root: The first screening of corn roots was done at 21 C within a gradient of 4.2 C cm*K The mean orientation of the roots within the gradient was 47° from the vertical towards the warm side and was significantly different from the control which was O.4° from the vertical. The magnitude of the response was such that subsequent experiments involving four other exposure temperatures were set up. The orientation of corn primary roots in the 4.2 C cm”1 gradient were also significantly different from their respective controls at 9.0, 14.7, 21.0 and 26.4 C but not at 32.1 C (Figure 3.2). Since corn primary roots grew faster at 32 C than at any other temperatures (Figure 3.3), the absence of response cannot be accounted for by a unfavorable growth rate. As indicated by the positive sign of the angles difference in Figure 3.2, in all cases where the responses were significantly different from the control, the root tip orientation was towards the warm side. A similar set of experiments at a gradient of 2.2 C cm‘l showed an absence of response at 26.8 C cm‘1 and responses towards the warm side, significantly different from the control at temperatures 14.7 to 24.0 C (Figure 3.2). A third and fourth set of experiments at temperatures of 14.7 and 21 C within gradients of 1.4 and 0.5 C cm‘1 also gave significant re-orientation of the 73 primary roots towards the warm side of the dish (Figure 3.2). The re-orientation angles at 14.7 and 21 C within the various gradient strengths described above were re-plotted as a function of stimulus strength (gradient) (Figure 3.4). The extent of the re-orientation of corn roots increases with the stimulus strength. The re- orientation also varies with the temperature of exposure: it is larger at 14.7 than at 21 C (Figure 3.4). Based on these observations tropic responses of corn roots to thermal gradients indeed exist. However, it is difficult to establish when a response to a thermal gradient is truly sensory as opposed to being a non- specific consequence of a differential effect of temperature on each side of the root. If the latter were the case, we should expect two types of responses: first, the most favorable temperatures for elongation growth should also be the temperatures with the highest curvature responses; second, the side of the root exposed to the most favorable temperature in terms of elongation should grow faster and as a consequence, the root should curve towards the opposite or cooler side. However, we observed the lowest curvatures at the temperatures of 26.4 and 32.1 C (Figure 3.2) which are the thermal conditions where elongation growth was the highest (Figure 3.3). Moreover, there exists a higher response at 14.7 than at 21 C, while the roots grew significantly less at 14.7 than 21 C (Figures 3.3, 3.4). Finally, while elongation growth is relatively independent of temperature in the 26-32 C range (Figure 3.3), the curvature is not, as shown by the different 74 responses at 26.4 and 32.1, at the 4.2 C cmfl-gradient and, the different responses at 26.4 C in gradients of 2.2 and 4.2 C cm*K Finally, all the significant curvatures are towards the warm side of the dish (positive sign of the angle), implying that the colder side of the roots grew faster, although the highest temperatures of exposure are clearly favoring growth in this experiment (Figure 3.3). Thus, it is very unlikely that the observed change in root direction is a passive consequence of the gradient across the root. Although the plates were sealed and roots grew at 100% humidity, the temperature gradient across the roots creates a moisture gradient since saturation vapor pressure increases with temperature. This is of concern since Jaffe et a1. (1985) showed that a root gravitropic mutant of pea could sense moisture gradients and re-orient its roots towards high humidity zones. However, the curvatures at 14.7 C were much higher than at 32.1 C in the highest gradient (4.2 C cm*0 (Figure 3.2), but yet the vapor pressure at 32.1 C is twice that at 14.7 C (Fritschen and Gay, 1979); also, the 32.1 C temperature of exposure at 4.2 C cm'1 gave a response similar to that of 26.1 C at 2.2 C cm‘1, while under a hydrotropism situation, it would be expected that the highest temperature at the highest gradient would show a higher response. Therefore, the curves of Figure 3.2, would be expected to increase with temperature rather than decrease. Based on these observations, it can be argued that hydrotropism is of little consequence in our experiments. 75 Further characterization of this phenomenon is needed. For example, it remains to be seen if the degree of root re-orientation varies with pre-treatment temperatures and if orientation towards cold temperature can exist as it has been shown with different thermotactic systems such as Parameeiam £££I§2££llé (Henessey and Nelson, 1979), E. eel; (Maeda et al., 1976), and Dictyosteliam diseoideum (Whitaker and Poff, 1980). Some similarities with microbial systems exist since the temperatures at which Dictyostelium becomes insensitive to a thermal gradient decrease as the stimulus strength decreases (Whitaker and Poff, 1980). This trend is also true for corn (Figure 3.2). As well, the response of Dictyostelium increases with gradient strength (Fontana and Poff, 1984) which has been noted with corn too (Figure 3.4). Finally, it is interesting to note that the temperatures at which corn did not have a response to the thermal gradients correspond to the optimal temperature for corn root growth (Cooper, 1973). Meanwhile, the range of temperatures where maximal responses were measured, corresponds to spring and early summer seed zone temperatures typical of the northern regions where corn is grown. Under circumstances where horizontal temperature gradients would exist (non-uniform placement of residues, row cropping, raised beds, ridge tillage), root thermotropism could be of adaptive value. 76 Arabidopsis thaliana root: The question remains whether thermotropism interacts with gravitropism such that the curvature is the result of a vector sum of 2 forces orthogonal to each other. Since this question cannot be answered directly with corn, Azahieenaia was used in another series of experiments since shoot and root gravitropism mutants are available. However, a preliminary test of Alfihiéflfliifi wild-type at 21 C in the strong gradient of 4.2 Ccmfl-resulted in a low curvature response. In order to enhance the response, two pre-treatment germination temperatures, 5 C above and below the treatment 21 C temperature were used for both the wild-type and the mutant strain, characterized as randomly orienting its hypocotyl and root in a l-g environment (Bullen et al., 1989). The underlying hypotheses for such treatments were that the response could depend on the temperature to which the plant was growing prior to the thermal gradient treatment and/or that gravitropism may have been "masking" the response to the treatment. For both the wild-type and the gravitropism mutant, there was no significant interaction between the germination temperature and the gradient treatments. Thus, the two sets of treatments will be discussed separately. The root direction of bath genotypes showed different responses to the thermal gradient. The wild-type roots were more horizontal within the gradient than with the control. The wild- type control was 5° away from the vertical towards the cold side while the plants in the gradient treatment were 18° away from the 77 vertical towards the cold side (Table 3.1). The direction of the mutant roots within the gradient was not significantly different than that of the control mutant roots (Table 3.1). It appears that in the wild type genotype, the plants subjected to the gradient were about 13° more horizontal than their controls, suggesting that there is a significantly different orientation of the roots towards the cold side in Agaeigeeaia. The wiggliness of the roots exposed to the gradient was significantly higher (higher rate of change of curvature) than that of the controls in the wild type and also in the mutant plants (Table 3.1). The root lengths of the two genotypes were higher for the control plants than for the plants on the gradient. This growth rate difference may be a result of the plants within the gradient growing more directly towards the cold side of the gradient, at least in the case of the wild-type. There is a difference in the extent to which both genotypes express their root orientation in the gradient relative to their respective controls. Since there is evidence that the mutant strain is the result of a single recessive nuclear mutation (B. Bullen, personal communication), it can be implied that A£§hié22§1§ root behavior in the gradient is not independent of gravity sensing. The root direction and wiggliness of both genotypes were not affected by the germination temperatures (Table 3.2). 78 Arabidopsis thaliana hypocotyl: The small size of the Arabidopaia seed permitted the measurement of the hypocotyl direction, length and wiggliness in addition to the root measurements. There was no significant interaction between the germination temperature and the gradient treatments for both genotypes. The hypocotyl direction was not affected by the gradient treatment for either the wild-type or the mutant (Table 3.3). However, the wiggliness was significantly higher in the gradient (Table 3.3). As for the roots, the hypocotyls of mutant plants have a higher wiggliness than the wild-type, which is an expected consequence from the curving phenotype of a gravitropism mutant. The germination temperatures had no effect on the hypocotyl direction of either genotypes or on wild-type wiggliness but the mutant plants exhibited higher wiggliness with the 16 C germination temperature than the 26 C (Table 3.4). In summary, the wild-type root showed a higher curving frequency (wiggliness) and is more horizontal by 13° when grown at 21 C in a 4.2 Ccm’1 than at constant 21 C. The wild-type hypocotyl did not exhibit any change in direction but did have a higher curving frequency in the gradient. The pre-treatment temperatures did not have any effect apart from diminishing the growth rate of the plants. Therefore, if thermosensing exists in Azaeieeeeia, it is probably more prevalent in roots than hypocotyls. In general, the use of the mutant genotype did not enhance the responses (in terms of direction and wiggliness) to the thermal gradient. Thus, 79 it cannot be argued that it is gravity that limits the response of Agaeigeeeia to a gradient as high as 4.2 C cm*K In.fact, there was an absence of mutant root responses (direction) to the thermal gradient while there was a significant one in the wild-type. This absence of mutant response to thermal gradients could be attributed to the mutation and, assuming that thermotropism exists to a limited extent in Arabidopsis, the absence of response in the mutant for both thermal gradients and gravity suggests that thermotropism and gravitropism share part of the same signal transduction pathway. On the other hand, in general, the frequency of curvature (wiggliness) of roots and hypocotyls was affected to the same degree by the thermal gradients for the wild-type and the mutant. Thus, there was no interaction of gravity sensing and thermal gradients for the wiggliness criterion. It must be concluded that our hypotheses that that germination temperature could affect the response and that use of the mutant would lead to an enhanced response were not correct. Since the root of Arabidepaie has the potential of being only sligthly thermotropic, ALQDLQQRéLfi should not be considered as a model system with which we can better understand the thermotropic responses observed in corn. The differences observed between the two species in these experiments emphasizes the fact that root thermotropism is expressed under certain sets of conditions and not under others. Agahieepeia ecotype Estland, could be screened for thermal gradient responses at other temperatures than at 21 C but its practical 80 range of growth temperatures is limited (16 to 32 C). Meanwhile corn responses can be characterized under a broader range (9 to 40 C) (Cooper, 1973). There could be a correlation between the extent of the range of growth temperature and the extent of root thermotropism in a number of species. Further characterization of a number of species would be necessary before such a conclusion could be drawn. 81 Table 3.1 Effect of a 4.2 C cm'1 temperature gradient on root length, direction and wiggliness of a wild-type (WT) and gravitropism mutant (GM) of Arabidopaig egaliaaa Table 3.2 (L.) Heynh. Length Direction Wiggliness (cm) (') Treatment W.T. G.M. W.T. G.M. W.T. G.M. Gradient 2.1 2.8 -18 -1 11.8 14.0 Control 2.8 2.4 -5 6 6.3 10.3 Lsd (0.05) 0.2 0.1 6 ns 1.2 1.3 ns: non-significant Effect of germination temperature on root length, direction and wiggliness of a wild-type (WT) and gravitropism mutant (GM) of Arabidopsia ghaliana (L.) Heynh. Length Direction Wiggliness (cm) (') Treatment W.T. G.M. W.T. G.M. W.T. G.M. 16 C 1.8 1.2 -10 5 8.4 10.3 26 C .3.1 2.7 -7 3 7.6 10.8 Lsd (0.05) 1.0 0.5 ns ns ns ns ns: non-significant 82 Table 3.3 Effect of a 4.2 C ctn'1 temperature gradient on shoot length, direction and wiggliness of a wild-type (WT) and gravitropism mutant (GM) of AIéthQEfiii thaliana (L.) Heynh. Length Direction Wiggliness (cm) (') Treatment 'W.T. G.M. W.T. G.M. W.T. G.M. Gradient 3.1 2.1 0 -4 7.7 10.5 Control 3.3 2.4 3 6 5.0 9.1 Lsd (0.05) 0.1 0.1 ns ns 0.6 1.2 ns: non-significant Table 3.4 Effect of germination temperature on shoot length, direction and wiggliness of a wild-type (WT) and gravitropism mutant (GM) of Arabidopais ghaliaaa (L.) Heynh. Length Direction Wiggliness (cm) (') ‘ Treatment W.T. G.M. W.T. G.M. W.T. G.M. 16 C 2.3 1.2 1 3 6.6 12.2 26 C 3.8 2.8 3 3 5.3 8.3 Lsd (0.05) 0.9 0.8 ns ns ns 2.3 ns: non-significant 83 4-—— coleoptile i