Effects Of Seasonal Drought On Physiology And Growth Of Betula Platyphylla

Affected by global climate change,drought threatens the survival of plants.Many plants face seasonal droughts,which can affect key physiological processes in plants.In order to explore the effects of seasonal drought on physiology and growth of plants,this paper takes Betula platyphylla in Northeast China as the research material,by use the balance method and photometer method to calibrates the thermal disspation probes,measures the specific coefficient of thermal disspation technology of Betula platyphylla,and discusses the differences between calibration methods.Sap flow,leaf water potential,radial growth and fine root non-structural carbohydrates of B.platyphylla under seasonal droughts were measured,to explored the effect by seasonal drought on water use and fine root non-structural carbohydrates and growth of B.platyphylla.By measuring the root respiration of B.platyphylla plantations in Caohekou area with high precipitation and Maoershan area with low precipitation,the effect of precipitation on the root respiration of B.platyphylla plantation was discussed.The results are as follows:(1)Calibration of Betula platyphylla using the balance method and photometer method has obtained coefficients different from those proposed by Granier.Using the balance method?=115.59788,?=1.1748,using the photometer method ?=93.49238,?=1.04647.The Fs calculated by photometer coefficients and the K in the balance method is linearly regressed the observed Fs in balance method.The regression line is biased toward the observed Fs as the value increases,indicating that the potometer method is underestimated the true Fs compared to the balance method.(2)The response of B.platyphylla to seasonal droughts was obvious.The B.platyphylla's transpiration and radial growth experienced drought in the early growing season were significantly lower than those of B.platyphylla with normal water supply,and the content of soluble sugar and starch in fine roots was not significantly different from that of B.platyphylla with normal water supply.The transpiration of B.platyphylla that experienced drought in the late growing season was significantly lower than that of B.platyphylla with normal water supply.Radial growth,fine root soluble sugar and starch content were not significantly different from those of normal watered B.platyphylla.The B.platyphylla's transpiration,daily transpiration and its correlation with environmental factors,transpiration rate and daily change,and leaf water potential were consistent with water supply conditions,that is,drought inhibited the water use and growth of B.platyphylla.Growth of the Betula platyphylla in early growth season is related to transpiration,while growth in late growth season is not significantly related to transpiration.The content of fine root non-structural carbohydrates was not significantly different among the groups.(3)Root CO2 efflux rate decreased significantly(P<0.01)with the increase of diameter class.In the Caohekou experimental site with high precipitation,after removing the influence of root temperature during measurement,the root respiration rate of diameters<0.5mm and diameter>5.0mm was significantly(P<0.05)higher than that of the Maoershan experimental site with lower precipitation.The root CO2 efflux rates of B.platyphylla in Caohekou and Maoershan with diameters<0.5mm were 107.38 and 82.05 ?mol·g-1·s-1,the root CO2 efflux rates with diameters>5.0mm were 25.04 and 11.14 ?mol·g-1·s-1,respectively.Based on the above results,this research illustrates the necessity of the calibration.The use of the Granier coefficient without calibration will cause deviation estimation of plant transpiration.Drought in the early growth season affects the plant growth process,and plants reduce transpiration through stomatal regulation and allocate more carbon to underground parts.Drought in the late growing season has no significant effect on plant growth,plants may preferentially allocate carbon to reproductive organs as they endure late drought.Root diameter and soil moisture have significant effects on root respiration of forest trees.This study is of great significance for accurate calculation of transpiration,understanding of drought resistance strategies of plants under seasonal drought,and accurate estimation of root respiration.