Peddinti Srinivasa Rao, Kisekka Isaya
Department of Land, Air & Water Resources, University of California Davis, Davis, CA 95616, USA.
Department of Land, Air & Water Resources, University of California Davis, Davis, CA 95616, USA; Department of Biological and Agricultural Engineering, University of California Davis, Davis, CA 95616, USA.
Sci Total Environ. 2025 Jun 18;990:179914. doi: 10.1016/j.scitotenv.2025.179914.
Water use efficiency (WUE) at the ecosystem level is a critical ecophysiological indicator that integrates carbon-water coupling processes and provides essential insights for sustainable agriculture in water-limited environments. This study investigated the dynamics of WUE in California almond orchards, a high-value and water-intensive crop system of global economic significance, by combining eddy covariance (EC) measurements with satellite remote sensing to analyze seasonal and interannual patterns from 2020 to 2022. Gross primary productivity (GPP) was estimated using the Vegetation Photosynthesis Model (VPM), while evapotranspiration (ET) was derived using the pySEBAL surface energy balance model applied to Landsat imagery. The ratio of these fluxes provided spatially distributed WUE estimates. Daily GPP ranged from ~0.5 to 11.5 g C m d, while ET ranged from ~0.5 to 7.5 mm d, with both fluxes peaking during mid-summer. WUE values exhibited distinct seasonal patterns (ranging from ~0.5 to 5.9 g C kg HO), with higher efficiency during dormancy and lower values during fruit development stages, averaging 2.14 g C kg HO over the study period. GPP and ET showed similar seasonal patterns and responded in tandem to key climatic variables (solar radiation, air temperature, and humidity), suggesting common environmental drivers govern these processes. WUE exhibited more complex behavior: it increased slightly with greater precipitation and humidity and declined under high solar radiation, high vapor pressure deficit (VPD), and extreme temperatures. The remote sensing-derived GPP and ET agreed well with EC tower measurements (R ≈ 0.87-0.88), affirming the reliability of the integrated approach. This study advances our understanding of carbon-water coupling in perennial almond orchard systems. It provides valuable ecological indicators for precision irrigation management in the face of increasing water scarcity and climate variability.
生态系统层面的水分利用效率（WUE）是一个关键的生态生理指标，它整合了碳-水耦合过程，并为水资源有限环境下的可持续农业提供了重要见解。本研究通过将涡度相关（EC）测量与卫星遥感相结合，分析了2020年至2022年的季节和年际模式，从而研究了加利福尼亚杏仁园（一个具有全球经济意义的高价值且耗水的作物系统）中WUE的动态变化。利用植被光合作用模型（VPM）估算总初级生产力（GPP），而蒸散量（ET）则通过应用于陆地卫星图像的pySEBAL表面能量平衡模型得出。这些通量的比值提供了空间分布的WUE估算值。每日GPP范围约为0.5至11.5 g C m⁻² d⁻¹，而ET范围约为0.5至7.5 mm d⁻¹，两者通量均在仲夏达到峰值。WUE值呈现出明显的季节模式（范围约为0.5至5.9 g C kg⁻¹ H₂O），休眠期效率较高，果实发育阶段效率较低，研究期间平均为2.14 g C kg⁻¹ H₂O。GPP和ET表现出相似的季节模式，并对关键气候变量（太阳辐射、气温和湿度）同步响应，表明共同的环境驱动因素控制着这些过程。WUE表现出更复杂的行为：随着降水量和湿度增加略有上升，而在高太阳辐射、高水汽压差（VPD）和极端温度下下降。遥感得出的GPP和ET与EC塔测量结果吻合良好（R≈0.87 - 0.88），证实了综合方法的可靠性。本研究推进了我们对多年生杏仁园系统中碳-水耦合的理解。它为面对日益严重的水资源短缺和气候变异性时的精准灌溉管理提供了有价值的生态指标。
