Conifers response to water stress : physiological responses and effects on nutrient use physiology

"Conifer species are the most extensively distributed on earth, and they are one of the most significant renewable resources with high economic value. Conifer species, Pinus and Abies species have been gaining popularity due to their desirable green color for products such as Christmas trees and are extensively used in landscaping. Not only inhabiting forest in their natural habitat, but also in plantations and reforestation areas usually outside their natural range where they have been exposed to water stress due to water shortage and the effects of climate change. Water stress is an important environmental factor for tree growth and development in plants. Therefore, we investigated the effect of irrigation and fertilization on balsam (Abies balsamae) and concolor fir (Abies concolor) and white pine (Pinus strobus ) seedlings in terms of tree morphology and physiology using a factorial design with three species and irrigation levels and two fertilization rates. Increased irrigation not only increased morphological traits such as diameter and height growth but also increased the net photosynthesis and stomatal conductance. The combination of each treatments had 5 seedlings for fir species and 4 seedlings for the pine species totaling 168 individual trees. White pine and balsam fir showed some drought tolerant mechanisms where concolor fir exhibited drought avoidance mechanisms. Fir species had higher net photosynthesis, stomatal conductance, transpiration rate and a lower water use efficiency compared to white pine. White pine had lower potassium concentration compared to two fir species, and balsam fir had higher calcium concentration compared to white pine and concolor fir under stress conditions, implying that fir species are more susceptible to water stress. We observed that concolor fir had a greater capacity for conserving water compared to white pine, leading to better above ground growth and shoot to root ratio. Balsam and concolor fir also had a greater foliar nitrogen concentration compared to white pine seedlings due to using an avoidance mechanism and maintaining nutrient uptake under water deficit conditions. White pine trees use drought tolerance strategies to reduce transpiration and maximize water uptake with increased root systems. White pine trees had higher below-ground biomass, with increased fine and coarse roots, and a lower nutrient use efficiency compared to two fir species. Moreover, we also tested the provenance and altitudinal variation of Turkish fir seedlings under water stress conditions. Morphological traits, such as relative root collar diameter, relative height growth, and stem volume index differed with seed source altitude as transplants from higher seed sources altitudes had greater growth compared to seedlings from lower altitudes. Overall, provenance had little effect on physiological parameters such as net photosynthesis, stomatal conductance, transpiration rate, internal CO2/ambient CO2 ratio, water use efficiency (WUE= A/E) and intrinsic water use efficiency (WUEi = A/gs), chlorophyll fluorescence (Fv/Fm) and carbon isotope discrimination rate (Delta13C). Provenances varied in stem water potential and net photosynthesis. Seedlings from the Karabuk provenances had high stem water potential and net photosynthesis. Intrinsic water use increased with altitude of the seed sources as seedlings from higher altitudes showed higher values compared to lower altitudes. Karabuk provenances might be more sensitive to water availability than Adapazari provenances. Adapazari provenances should be selected for the plantation and afforestation areas and production of Christmas trees."--Pages ii-iii.