大气干燥主导了中纬度森林的昼夜碳水耦合。

摘要(中文译文)

北半球的中纬度森林生态系统是巨大的碳汇，也具有强大的蒸腾能力，使其成为全球碳和水循环的关键组成部分。然而，中纬度森林的昼夜碳水耦合强度及其对环境因素的依赖性尚不清楚。基于位于30°之间的森林生态系统上34个涡流协方差（EC）塔的半小时通量数据 N和60° N、 在这里，我们通过相关性分析、岭回归和数据分箱研究了昼夜碳水耦合强度的特征及其对环境因素的响应，即太阳辐射（SR）、气温（Ta）、蒸汽压差（VPD）和土壤含水量（SWC）。我们发现，总初级生产力（GPP）和蒸散量（ET）之间的日变化存在明显差异，GPP在峰值后通常比ET更早、更快地下降。SR、Ta或VPD的增加会导致日间耦合强度的降低，而较高的SWC会使耦合更强。VPD和Ta的负面影响程度在一天中有所不同，下午的VPD是最有影响的因素，Ta在清晨起着主导作用。在34个位点中，VPD是影响30个位点耦合强度的主要因素，而Ta在三分之一的研究位点中是次要因素。耦合强度的减弱归因于GPP和ET对环境因素的异步响应，特别是在高VPD和温度条件下，当GPP趋于降低而ET不跟随时。本研究强调了昼夜碳水耦合的动态以及与环境因素的复杂相互作用，强调在未来的研究中需要考虑不同生态系统中GPP和ET耦合对环境因素的短期响应。

Abstract

Mid-latitude forest ecosystems in the Northern Hemisphere serve as substantial carbon sinks and also hold a strong transpiration capacity, making them critical components of the global carbon and water cycles. However, the diurnal carbon-water coupling strength over mid-latitude forests and its dependence on environmental factors are unclear. Based on half-hourly flux data from 34 eddy covariance (EC) towers over forest ecosystems located between 30° N and 60° N, here we investigate the characteristics of diurnal carbon-water coupling strength and its response to environmental factors, that is, solar radiation (SR), air temperature (T), vapor pressure deficit (VPD), and soil water content (SWC) through correlation analysis, ridge regression, and data binning. We find that there is a distinct difference in diurnal variation between gross primary productivity (GPP) and evapotranspiration (ET), with GPP generally decreasing earlier and faster than ET after its peak. An increase in SR, T, or VPD can lead to a reduction in the diurnal coupling strength, while higher SWC makes the coupling stronger. The magnitudes of the negative effects of VPD and T vary across the day, with VPD in the afternoon being the most influential factor and T playing a dominant role in the early morning. Among the 34 sites, VPD is the dominant factor influencing coupling strength at 30 sites, while T is secondarily important over one-third of the studied sites. The weakening of coupling strength is attributed to the asynchronous responses of GPP and ET to environmental factors, particularly under conditions of high VPD and temperature, when GPP tends to decrease while ET does not follow. This study highlights the dynamics of diurnal carbon-water coupling and the complex interactions with environmental factors, emphasizing the need to consider the short-term responses of GPP and ET coupling to environmental factors across diverse ecosystems in future research.

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