亚热带地区常绿阔叶林SPAC系统水分的氢氧稳定同位素特征

Hydrogen and oxygen stable isotope characteristics of water in SPAC system of evergreen broadleaved forest in subtropical region

森林的土壤-植物-大气连续体(SPAC)是陆地重要的水循环连续界面过程。本研究通过分析亚热带常绿阔叶林的降水、大气水汽、土壤水、叶片水的同位素组成,探讨森林SPAC系统水分的氢氧同位素组成特征以及植物蒸腾与叶片性状和环境因子的关系。结果表明:研究区大气降水、土壤水、竹柏枝条水、竹柏叶片水和大气水汽的δD-δ^(18)O线性回归方程分别为:δD_P=7.97δ^(18)O_P+12.68(R^2=0.97)、δD_S=4.29δ^(18)O_S-18.62(R^2=0.81)、δD_B=3.31δ^(18)O_B-29.73(R^2=0.49)、δD_L=1.49δ^(18)O_L-10.09(R^2=0.81)、δD_V=3.89δ^(18)O_V-51.29(R^2=0.46)。在降水→土壤水→植物水的界面水输送过程中,氢氧同位素逐渐富集,而从土壤蒸发和从植物蒸腾的水汽同位素贫化。在降水和蒸发作用的影响下,土壤水同位素随深度增加有贫化的趋势,而且整体上旱季土壤水同位素比雨季富集。观测期间,枝条水同位素比土壤水略微富集,说明水分在植物体内运输过程中存在受到蒸腾富集作用的可能性。旱季,乔木的枝条水同位素比灌木贫化,说明根系分布更深的乔木植物更倾向于利用深层土壤水。由于在叶片性状、蒸腾速率以及对环境因子的响应程度等方面存在差异,不同植物的叶片水同位素组成随叶龄增长的变化特征有所不同。雨季的环境条件更有利于叶片蒸腾,使雨季的叶片水同位素比旱季富集。叶片水同位素组成与植物叶片含水量呈正相关关系,与相对湿度呈负相关关系,综合反映了植物应对环境变化的水分调控功能。

Forest soil-plant-atmosphere continuum(SPAC)is an important continuous process of water cycle.In this study,we analyzed hydrogen and oxygen stable isotope compositions of the precipitation,atmospheric water vapor,soil water,branch water,and leaf water to explain the characteristics of the continuous process and the associated controlling factors in a subtropical evergreen broadleaved forest.The results showed that the regression equations between hydrogen and oxygen stable isotopes wereδDP=7.97δ18OP+12.68(R2=0.97)for precipitation,δDS=4.29δ18OS-18.62(R2=0.81)for soil water,δDB=3.31δ18OB-29.73(R2=0.49)for branch water andδDL=1.49δ18OL-10.09(R2=0.81)for leaf water of Podocarpus nagi,δDV=3.89δ18OV-51.29(R2=0.46)for atmospheric water vapor,respectively.In the process of water transport from precipitation to soil water to plant water,hydrogen and oxygen isotopes gradually enrich,while water vapor isotopes evaporated from soil and evaporated from plants were depleted.With the influence of precipitation and evaporation,soil water isotopes depleted with depth,and more enriched in the dry season than that in the rainy season.During the observation period,isotope content of branch water was slightly higher than that of soil water,indicating that water might be enriched by transpiration during the transportation process in plants.In the dry season,water isotope in branches of arbor plants was poorer than that of shrubs,indicating that arbor plants with deeper root distribution tended to use deep soil water.Because of the differences of leaf traits,transpiration rate and the response degree of environmental factors,the variation characteristics of water isotope composition in leaves of diffe-rent plants varied with the increases of leaf age.Environmental conditions in rainy season were more conducive to leaf transpiration,which made leaf water isotope enriched in rainy season than in dry season.The isotopic compositions in leaf water of Podocarpus nagi had a positive relationship with leaf water content(LWC),and a negative one with relative humidity,reflecting the water regulation function of plants in response to environmental changes.