新安江源区典型植物稳定氢氧同位素组成特征

The characteristics of hydrogen and oxygen stable isotopes of typical plants in the source area of Xin’an River.

为了解暴雨时期亚热带森林生态系统水分在植物体内运移转换过程中同位素组成的变化特征以及对环境的响应机制,基于2020年7月梅汛期新安江源区亚热带常绿针叶林典型植物氢氧稳定同位素测试,结合黄山水文站涡动通量塔环境要素监测数据,分析了代表性树种杉木(Cunninghamia lanceolata)不同部位(根、皮、枝、叶)和样地多种优势植物叶片水同位素组成(δ^(18)O和δ^(2)H)的日间变化特征及δ^(18)O-δ^(2)H相关关系,并讨论了不同植物叶片水δ^(18)O和δ^(2)H的环境控制因子。结果表明:杉木根、皮及枝水分同位素组成较为接近且日间变化平缓,叶片水同位素最为富集且日间变幅较大。受随机性强降雨影响,7月2—4日各来源δ^(18)O和δ^(2)H昼间变化无显著一致性规律,三日分别大致呈单峰型、单谷型和波动型变化。5种典型植物叶片水δ^(18)O-δ^(2)H线性回归得出的蒸腾线斜率从高到低依次为:狗脊(Woodwardia japonica)、茶(Camellia sinensis)、大豆(Glycine max)、杉木、毛竹(Phyllostachys heterocycla),说明毛竹叶水同位素动力分馏效应最强,狗脊最弱。各植物叶片水δ^(18)O和δ^(2)H的环境控制因子有所差异,杉木和狗脊叶片水δ^(18)O和δ^(2)H对土壤含水率和土壤温度的变化最敏感,气温和净辐射则是影响茶和大豆叶片水δ^(18)O和δ^(2)H的主导因子,毛竹叶水δ^(18)O和δ^(2)H与气温、相对湿度、土壤温度、土壤含水率和风速的相关性较强。研究结果有助于明晰湿润区生态水文过程,并为进一步构建同位素水文模型提供数据支持。

To clarify the variations of water isotopic composition and mechanism underlying their responses to environmental factors during water transport and conversion in subtropical forest ecosystems in heavy rain periods,we measured the hydrogen and oxygen stable isotopes of typical species in the subtropical evergreen coniferous forest across the source area of Xin’an River during the East Asian rainy season in 2020.Combined with the environmental factors monitored by the eddy covariance measurements of Huangshan Hydrological Station,we analyzed the diurnal variation of water isotopic compositions(δ^(18)O andδ^(2)H)in different parts(roots,bark,xylem and leaves)of Cunninghamia lanceolata and the correlation betweenδ^(18)O andδ^(2)H in leaf water of other dominant species in 2nd-4th July.The main environmental controlling factors of leaf waterδ^(18)O andδ^(2)H in different plants were investigated.The results showed that on the diurnal scale,water isotopic compositions of roots,bark,and xylem were similar and changed gently,while the isotopes in leaf water were most enriched and changed dramatically.Influenced by the random heavy rainfall,there was no significant consistency in the diurnal variations inδ^(18)O andδ^(2)H from different sources,showing single peak,single valley and fluctuation in each day of 2nd-4th July respectively.By linear regression of leaf waterδ^(18)O-δ^(2)H,the slopes of the transpiration line of five dominant species from high to low were as follows:Woodwardia japonica,Camellia sinensis,Glycine max,Cunninghamia,lanceolata,Phyllostachys heterocycla,indicating that water isotope fractionation effect was the strongest in Phyllostachys heterocycla and the weakest in Woodwardia japonica.The environmental controlling factors ofδ^(18)O andδ^(2)H were different among the five species.Soil moisture and soil temperature were the dominant factors affectingδ^(18)O andδ^(2)H in leaf water of Cunninghamia lanceolata and Woodwardia japonica,while air temperature and net radiation were the main factors affectingδ^(18)O andδ^(2)H in leaf water of Camellia sinensis and Glycine max.Theδ^(18)O andδ^(2)H in leaf water of Phyllostachys heterocycla were strongly correlated with air temperature,relative humidity,soil temperature,soil moisture,and wind speed.The results are helpful to clarify the eco-hydrological process in humid region and provide data support for further establishing isotope hydrological model.