北京土石山区水分在土壤-植物-大气连续体(SPAC)中的稳定同位素特征

Stable hydrogen and oxygen isotope compositions in soil-plant-atmosphere continuum (SPAC) in rocky mountain area of Beijing,China

氢氧稳定同位素是广泛存在于自然界水体中的环境同位素,其在不同水体中组成特征的差异可以指示水分循环过程及植物用水机制.本研究在北京山区选取了两种主要的绿化树种——常绿针叶林侧柏和落叶阔叶林栓皮栎为研究对象,通过对降水、土壤水、泉水、植物茎干水和叶片水同位素的变化特征进行分析,讨论了水分在大气-土壤-植物连续体中的运动过程.结果表明:研究区大气降水线方程为δD=7.17δ^(18)O+1.45(R2=0.93),土壤蒸发线方程为δD=3.85δ^(18)O-38.02(R^2=0.76),降水入渗补给土壤水的过程中存在一定程度的蒸发分馏.在不同季节,降水、土壤水和泉水δD和δ^(18)O值变化规律不同;雨季,δD和δ^(18)O平均值大小为降水>地下水>土壤水,降水和土壤水共同补充地下水;旱季,δD和δ^(18)O值大小排序为降水>土壤水>地下水,降水和地下水都对土壤水有贡献.侧柏和栓皮栎年内茎干水分δD和δ^(18)O的拟合线性方程分别为δD=5.03δ^(18)O-30.78和δD=3.0δ^(18)O-48.92,栓皮栎利用的土壤水分相对于侧柏更加富集,其水分来源深度更浅.栓皮栎叶片水分同位素变化特征相对于侧柏对大气微环境的反应更加敏感,且其叶片水分蒸发和同位素动力分馏程度更强,但是它们对环境条件的变化反应一致.

The stable hydrogen and oxygen isotopes are environmental isotopes, which widely exist in various kinds of water. Their relative abundance variation in water can indicate the water circula- tion and mechanism of water use in plant. This research selected two major kinds of greening tree species, evergreen coniferous Platycladus orientalis and deciduous broad-leaved Quercus variabilis, in Beijing mountainous area, and the water movement process in soil-plant-atmosphere continuum was investigated by the variation characteristics analysis of stable hydrogen and oxygen isotope com- positions in precipitation, soil water, groundwater, plant stem water and leaf water. The results showed that the meteoric water line equation of the study area was δD = 7.17δ18O＋ 1.45 （R^2= 0.93）, and the soil evaporation line equation was δD= 3.85δ18O＋1.45 （R2= 0.76）. A certain de- gree of evaporation fractionation existed in the processes of rainfall infiltration into soil water. In dif- ferent seasons, the δD and δ18O values of precipitation, soil water and spring water had different variation regularity. In rainy season, the mean δD and δ18O values were in order of precipitation〉 sprin~ water〉soil water, with the precipitation and soil water supplied sprinz water together： in dry season, the order was precipitation 〉 soil water 〉 spring water, and the precipitation and spring wa- ter both contributed to soil water. The δD and δ18O fitting line equations of stem water of P. orienta- l/s and Q. variabilis were respectively δD= 5.0351So-30.78 and 6D= 3.0δ18O-48.92. The uptake water of Q. variabilis was more enriched than that of P. orientalis, and the depth of Q. variabilis wa- ter uptake in soil profile was shallower than P. orientalis. The leaf water isotopic variation of Q. varia- bilis was more sensitive to atmospheric environment, with the kinetic isotopic fractionation of Q. variabilis being more enriched than that of P. orientalis, but they had the same response to variation of environmental condition.