光温条件和土壤湿度对栓皮栎幼苗蒸腾潜热和叶温的影响

研究光温条件和土壤湿度对栓皮栎幼苗叶片蒸腾的影响程度,以及太阳辐射、蒸腾和对流换热对叶温形成的贡献.用盆栽遮雨和称量法,控制土壤干旱胁迫水平(体积含水量)为轻度(12.5％ ～ 14.5％)、中度(9.5％～11.5％)和重度(5.5％～7.5％),并分别在自然和人工气候箱(温度控制在25 ～ 43℃)的环境下测定蒸腾速率和气象因子;用热量分析方法,定量确定各因子对叶温差的贡献.结果表明:1)轻度干旱下,蒸腾速率与正常土壤水分下相近,重度干旱胁迫下蒸腾速率降到1.5 mmol/(m2·s)以下;2)晴天的蒸腾速率与太阳辐射关系密切,呈正相关,不同土壤水分胁迫下的斜率不同,表明太阳辐射是蒸腾的主导因子;3)多云天时,蒸腾速率与太阳辐射的线性关系明显下降,说明白天蒸腾一旦开始,蒸腾速率不因短时间的太阳辐射下降而降低;4)在3个土壤干旱水平下,气温都不是蒸腾的主导因子.人工气候箱试验条件下,蒸腾速率虽与气温线性关系明显,但蒸腾速率明显小于晴天自然条件下.同时也说明,轻度干旱不影响栓皮栎蒸腾;在静风条件下,太阳辐射是栓皮栎叶温变化的主导因子,可使叶温变化7℃左右,占叶温变化的50％～70％;蒸腾潜热和对流换热项可使叶温变化1 ～2℃左右,各占叶温变化的10％ ～20％.本研究为构建栓皮栎的WSI,以及用叶气温差诊断栓皮栎土壤水分提供理论依据.

Impacts of radiation,temperature and soil moisture on hidden heat of transpiration and leaf temperature of Quercus variabilis seedlings

Background] Drought threats plants' survival and in the same time it causes variation of their leaf temperature (TL),which provides people an efficient path to diagnose soil moisture.Many scholars have been using crop leaf-air temperature deficit (LATD) to calculate crop water stress index (CWSI).However,there are few studies on leaf-air temperature of Quercus variabilis,and no works on diagnose of soil moisture.The transpiration (Tr) of Q.variabilis is less than that of crops,and its LATD is larger than agricultural crop,thus the water stress index (WSI) of Q.variabilis should be different to CWSI.The key that uses LATD to evaluate water stress is to analyze the energy factors of leaf temperature.Methods] Watering the pots then soil moisture decreased through natural evaporation,we controlled soil moisture in 3 levels:light drought,12.5％-14.5％ (W1);moderate drought,9.5％-11.5％ (W2),and severe drought,5.5％-7.5％ (W3).Selecting clear and cloudy days,from 8:00 to 18:00,we measured Tr and TL as well as air temperature (t) and solar radiation (R).We also measured Tr in artificial chamber controlling temperature at 25-43 ℃,at every 2 ℃ interval of treating temperature.According to the ratio of net radiation AR,convection Φc,latent heat of transpiration LE,and leaf area density ρ,heat capacity Cp:AR/ρCp,Φc/ρCp,LE/ρCp,we calculated the contribution of each energy item to TL.Results] 1) The Tr of W1 was close to of normal soil moisture,the maximum Tr was 2.5 mmol/(m2·s).The Tr of W2 and W3 reduced to be ＜ 1.5 mmol/(m2·s).2) In clear day,Tr positively related to solar radiation,which indicated that solar radiation was main factor of Tr.The slopes of the regression line between Tr and solar radiation were different with different soil moistures,the dryer the soil was,and the greater the slope was.3) In cloudy day,the relation coefficient between Tr and solar radiation decreased clearly,which meant Tr did not decline with short time interval of radiation reducing,once transpiration started in the morning.4) On any case of soil moisture,air temperature was not main factor of Tr.Though in artificial chamber the linear relation of Tr and temperature was clear,Tr was lower than natural clear day.Conclusions] 1) Light drought did not impact Tr of Q.variabilis.2) When wind speed was zero,solar radiation was main factor of leaf temperature variation.Net radiation accounted for 50％-70％ of energy budget,and provided approximately 7 ℃ of leaf temperature variation.3) The latent heat of Tr and convection heat exchange had an equal effect on energy budget,which accounted for 10％-20％ respectively.Each of two factors caused approximately 1-2 ℃ of leaf temperature variation respectively.