Climate change intensifies precipitation fluctuation and increases drought frequency around the globe. Water use efficiency (WUE) has proven to be a crucial metric to quantify the trade-off linking global carbon and water cycles in many aspects of terrestrial ecosystem function. Investigating the response of ecosystem WUE to multiannual precipitation fluctuations has major implications for our understanding of ecosystem carbon and water dynamics. However, the impacts of water availability variation on evapotranspiration- and transpiration-based ecosystem WUE and their mechanisms are poorly understood due to limited observations. We investigated ecosystem WUE in response to interannual precipitation fluctuations in order to reveal the regularity underlying WUE changes under different levels of water stress. We optimized the parameters of two remote sensing models (PT-JPL and PM) based on different biophysical processes using the differential-evolution Markov Chain (DE-MC) method. We investigated ecosystem WUE_ET (GPP/ET) and WUE_T (GPP/T) in response to interannual precipitation fluctuations at 73 sites. We found ecosystem WUE_T appears to decline during drought years and to increase in wet years contrasting with WUE_ET, which was mostly attributable to differing sensitivities of GPP, ET and T to multiannual precipitation fluctuations. The vegetation generally consumes more T to improve ecosystem GPP during dry years, meanwhile, no apparent change in WUE_ET during dry years because of the trade of between GPP/T and T/ET. The replenishment of soil moisture to ecosystem transpiration is higher than we thought during dry years. This was masked in analysis that considered the responses of GPP and T to annual precipitation changes separately, but was revealed by the changes in ecosystem WUE_T. This research advances our understanding of the consequences of water fluctuation on ecosystem carbon and water exchange.

气候变化加剧了降水的波动并增加了全球干旱的频率。事实证明，用水效率（WUE）是量化地球陆地生态系统功能的许多方面中全球碳和水循环之间的权衡取舍的关键指标。研究生态系统WUE对多年降水量波动的响应对我们对生态系统碳和水动力学的理解具有重要意义。然而，由于有限的观察，人们对水的可用性变化对基于蒸散和蒸腾的生态系统WUE及其机理的影响了解甚少。我们调查了响应于年际降水波动的生态系统WUE，以揭示不同水分胁迫水平下WUE变化的规律性。我们使用差分进化马尔可夫链（DE-MC）方法基于不同的生物物理过程优化了两个遥感模型（PT-JPL和PM）的参数。我们调查了生态系统WUE_ET（GPP / ET）和WUE _T（GPP / T）响应73个站点的年际降水波动。我们发现，与WUE _ET相比，生态系统WUE _T在干旱年份似乎有所下降，而在潮湿年份则有所增加，这主要归因于GPP，ET和T对多年降水波动的敏感性不同。干旱期间，植被通常消耗更多的T来改善生态系统GPP，与此同时，WUE _ET没有明显变化由于GPP / T和T / ET之间的交易，因此在干旱年份中，土壤水分对生态系统蒸腾的补充高于我们在干旱年份所认为的水平。分析中掩盖了这一点，该分析分别考虑了GPP和T对年降水量的响应，但通过生态系统WUE _T的变化揭示了这一点。这项研究提高了我们对水波动对生态系统碳和水交换的影响的理解。