基于对δ18O与δD的高频测量分解稻田生态系统蒸散发

Evapotranspiration (ET) partitioning is important for the scientific assessment of ecosystem productivity and the efficient allocation of increasingly scarce water resources under climate change scenarios. In the present project, we will partition ET into transpiration (E) and evaporation (E) using the novel isotope laser spectroscopy technique in rice paddies. We will (1) grow rice in growth chambers, measure the stable isotope of water vapor from T and E (δT and δE), compare δT and δE with those modeled from classical isotope models, identify the environmental conditions favorable to isotopic steady state (ISS), and clarify the underlying mechanisms that regulate δT and δE; (2) measure and model δT and δE in field, identify the environmental conditions favorable to ISS under natural circumstance, and assess the validity of ET partitioning for rice paddies with isotopic techniques; (3) measure net primary productivity (NPP), ET and the isotope signal of ET (δET) in rice paddy fields, and partition ET using a two end-member linear mixing model under ISS. The present project will also couple the isotopic measurements with photosynthetic analyses at the leaf scale, and address fundamental scaling issues by comparing leaf level measurements of WUE with ecosystem WUE. This project will undoubtedly advance our understanding of how biosphere-atmosphere water-carbon exchange respond to climate change, and will also provide practical guidance for water management in rice paddies.

蒸散发（ET）分解是气候变化背景下科学评估生态系统生产力与高效分配稀缺性淡水资源的重要基础。项目拟基于最新的稳定同位素激光光谱技术开展稻田生态系统ET分解研究：（1）生长室模拟种植水稻，控制环境因子，测量蒸腾（T）与蒸发（E）同位素组成（δT与δE），并与经典同位素模型拟合结果相比较，分析δT与δE变异调控机理，确定同位素稳态形成条件；（2）田间原位测量、拟合δT与δE，分析自然条件下δT与δE稳态维持情况，评估基于同位素技术分解稻田ET的可行性与有效性；（3）结合净初级生产力、ET以及ET同位素组成（δET）原位分析，采用二元线性混合模型，分解稻田ET。项目还将同步耦合光合碳同化测量，比较叶片与生态系统水分利用效率（WUE），阐述WUE尺度推广的有效性。该研究的开展有利于深化我们对生态系统碳水交换响应气候变化机理的科学认识；同时可为稻田水资源管理提供实践指导，具有重要的理论和现实意义。