Rice–wheat rotation cropland is one of the most important agroecosystems in South China, the escalation of conflict between food demand augment and water supply shortage increased with climate change. Water use efficiency plays a more significant role in optimising water and carbon management. Thus, the diurnal and seasonal variations of water use efficiency were assessed by the 3‐year eddy covariance observations in the Shouxian National Observatory, a typical rice–wheat rotation station. The results revealed a ‘U’‐shaped diurnal pattern of water use efficiency for winter wheat (Triticum aestivum L.) and rice (Oryza sativa L.). Seasonal water use efficiency had two peaks with the highest in the winter wheat‐growing season. The average water use efficiency for the rice–wheat rotation cropland was 2.85 g C kg−1 H2O over the whole year with 2.62 and 3.11 g C kg−1 H2O for winter wheat and rice, respectively. However, gross primary productivity and evapotranspiration of rice were higher than those of winter wheat. Temperature, photosynthetically active radiation were the principal impact factors of water use efficiency in the rice‐growing season. Comparatively, soil water and vapour pressure deficit dominated the water use efficiency changes in the winter wheat‐growing season. Our analyses can help understand the water use requirements for carbon assimilation on rice–wheat rotation cropland on the field scale.

中文翻译：

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江淮流域稻麦轮作农田水分利用效率的日变化和季节变化


稻麦轮作农田是华南地区最重要的农业生态系统之一，随着气候变化，粮食需求增加与水资源供应短缺之间的矛盾加剧。水资源利用效率在优化水和碳管理方面发挥着更重要的作用。因此，利用典型的稻麦轮作站寿县国家观测站的3年涡度协方差观测来评估水分利用效率的日变化和季节变化。结果显示，冬小麦 (Triticum aestivum L.) 和水稻 (Oryza sativa L.) 的水分利用效率呈现“U”形昼夜模式。季节性水分利用效率存在两个峰值，其中冬小麦生长季最高。稻麦轮作田全年平均水分利用效率为2.85 g C kg−1 H2O，冬小麦和水稻分别为2.62和3.11 g C kg−1 H2O。但水稻的总初级生产力和蒸散量均高于冬小麦。温度、光合有效辐射是水稻生长季水分利用效率的主要影响因素。相比之下，土壤水和水汽压亏缺主导了冬小麦生长季水分利用效率的变化。我们的分析可以帮助了解田间规模的稻麦轮作农田碳同化的用水需求。