北京山区侧柏林生长旺季蒸散组分δ^(18)O日变化及其定量区分  

Daily variations of δ^(18)O and its quantitative distinction in evapotranspiration components of Platycladus orientalis plantation during the rapid growth season in the mountainous area of Beijing

作　　者：刘璐[1] 贾国栋[1] 余新晓[1] 张永娥[1] LIU Lu;JIA Guo-dong;YU Xin-xiao;ZHANG Yong-e(Key Laboratory of State Forestry Administration on Soil and Water Conservation, Beijing Forestry University, Beijing, 100083, P. R. China.)

机构地区：[1]北京林业大学水土保持国家林业局重点实验室

出　　处：《北京林业大学学报》2017年第12期61-70,共10页Journal of Beijing Forestry University

基　　金：国家自然科学基金青年项目(41401013);国家自然科学基金重点项目(41430747);林果业生态环境功能提升协同创新中心(PXM2017_014207_000043)

摘　　要：侧柏是北京山区分布范围较广的典型针叶树种,研究侧柏林生长旺季蒸散过程及蒸散组分变化特征对了解该区陆地生态系统水汽交换、植被耗水需求具有重要意义。本研究利用稳定同位素技术于生长旺季(2016年8月)对侧柏林大气水汽δ^(18)O进行原位连续观测,同时选取4个典型晴天采集枝条和土壤样品并测定样品水中的δ^(18)O。结果表明:日尺度上,利用Craig-Gordon模型计算的土壤蒸发水汽氧同位素组成(δ_E)在4个测定日中均先增大后减小,δ_E介于-5.968%^-2.689%,最大峰值出现在12:00—14:00,而近地面大气相对湿度(h)先减小后增大,二者关系为δ_E=-0.03h^2+4.85h-209.5(R^2=0.55,n=32),表明h>75%时,环境相对湿度越大,同位素分馏效应越明显;基于稳态假设估算的植物蒸腾水汽氧同位素组成(δ_T)和Keeling曲线拟合的侧柏林蒸散水汽氧同位素组成(δ_(ET))分别介于-1.210%^-0.951%、-1.599%^-1.004%,日变化趋势复杂,日间变化差异大,但同一观测日内δ_T和δ_(ET)变化趋势基本一致,表明植物蒸腾非稳态可能对δ_T的估算产生偏离,δ_(ET)变化主要受δ_T影响;4个测定日中蒸腾量占总蒸散量的比例(F_T)介于90.14%~92.63%,说明研究区侧柏林生态系统生长旺季蒸散发绝大部分来自植物蒸腾。研究结果确定了基于日尺度的生长旺季植被蒸腾对蒸散的贡献率,为研究陆地生态系统水汽交换机制提供了有益参考,为区域森林生态建设和管理提供了科学依据。As the dominant coniferous tree species in the mountainous area of Beijing, it is imperative to have an insight into the evapotranspiration of Platycladus orientalis in the rapid growth season and its components for deeper understanding of atmospheric vapor exchange of terrestrial ecosystems and plant water demand. The variations of daily δ18 O in a Platycladus orientalis plantation during the rapid growth season and proportions of plant transpiration and soil evaporation to evapotranspiration were analyzed. The continuous water vapor stable isotope analyzer was used to measure δ18 O values of the atmospheric vapor in August, 2016. Mature and suberized twigs of plant and soil samples were collected and measured simultaneously to analyze δ18 O values of transpiration （δT ） and soil evaporation （δE ） , where δT and δE were determined respectively via the steady state hypothesis of isotope and the Craig-Gordon equation. The oxygen isotopic compositions of total evapotranspiration （δET ） could be estimated by a Keeling plot linear regression function. The results showed that： values of δE ranged from -5. 968% to -2. 689%, which rised firstly and then declined at the daily scale; and δ18 O values peaked between 12：00 and14：00, whereas the atmospheric relative humidity （ h） dropped firstly and then rised. The relationship between δE and h was δE = -0. 03h2 ＋4. 85h-209. 5 （R2 =0. 55,n=32）, which indicated that the isotopic fractionation was intensified with h when its value was above 75%. Although the diurnal variations of δET and δT values were complex and there was inconsistent variation tendency for the two in the four experimental days （ ranged from -1. 210% to -0. 951% and -1. 599% to -1. 004%, respectively） , both of them basically shared identical changing trend at the same observation days, suggesting that the evaluation of δT values was probably affected by non-steady state of stable isotopes in the leaf water. And the variations on δET were dominantly driven by �

关 键 词：侧柏林 生长旺季 蒸散发 同位素稳定态 

分 类 号：S791.38[农业科学—林木遗传育种] Q945.17[农业科学—林学]