Models overestimate ecosystem water use efficiency for northern permafrost regions
Models overestimate ecosystem water use efficiency for northern permafrost regions
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DOI：
10.1016/j.agrformet.2023.109594
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发表时间：
2023-08
影响因子：
6.2
通讯作者：
Jian Wang;Desheng Liu
中科院分区：
文献类型：
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作者：
Jian Wang;Desheng Liu
了解多年冻土区的碳-水耦合对于预测全球生态系统的碳固存和水动力学至关重要。生态系统水分利用效率(EWUE)是指总初级生产力(GPP)与蒸散量(ET)的比值，反映了不同生态系统对环境胁迫的适应策略。然而，北部多年冻土地区的EWUE变化及其潜在驱动因素的量化仍然很差，阻碍了我们对永久冻土碳−气候反馈的理解。在这里，我们利用卫星观测和基于过程的模型来比较和分析差异，以估计1982-2018年北方多年冻土区EWUE的时空变化。使用通量测量作为真实数据，卫星EWUE比基于模型的EWUE更可靠。来自卫星的EWUE表现出与生物群相关的空间格局，北部多年冻土区空间平均EWUE具有稳定的时间趋势(0.01g C mm−1ten−1，P&gT；0.05)。二氧化碳(CO2)浓度和氮沉降对EWUE年际变化有正向影响，而水汽压差和其他气候因子(如温度、降水和辐射)对EWUE有负控制作用。与来自卫星的EWUE相比，我们发现，从基于过程的碳循环模型集合得到的EWUE在十个模型中有七个被高估，对于集合平均值的空间平均EWUE，其趋势是增加0.11g C mm−110−−1(P<；(0.001))。气候因素和EWUE之间的关系在模式估计中被部分误解，特别是夸大了CO2的敏感性和相反的温度效应。对气候的敏感性随时间波动，以及二氧化碳施肥对总初级生产力(GPP)的影响减弱，这可能部分解释了卫星得出的EWUE估计值与基于模型的估计值之间的差异。因此，这项研究呼吁对基于模型的EWUE持谨慎态度，并有助于理解永久冻土气候反馈以及碳和水循环的预测。
Understanding the carbon-water coupling over permafrost regions is essential to projecting global ecosystem carbon sequestration and water dynamics. Ecosystem water use efficiency (EWUE), defined as the ratio of gross primary productivity (GPP) and evapotranspiration (ET), reflects plant acclimation strategies with varying ecosystem functioning against environmental stress. Yet EWUE change and its potential drivers across the northern permafrost regions remain poorly quantified, hampering our understanding of permafrost carbon−climate feedback. Here, we compared and analyzed the difference using satellite observations and process-based models to estimate the spatio-temporal variations of EWUE in 1982–2018 over northern permafrost regions. Using flux measurements as truth data, satellite-derived EWUE was more reliable than model-based EWUE. Satellite-derived EWUE showed biome-dependent spatial patterns, with a steady temporal trend (0.01 g C mm−1decade−1,P> 0.05) for spatially averaged EWUE over northern permafrost regions. Carbon dioxide (CO2) concentration and nitrogen deposition positively affected interannual variations of EWUE, while vapor pressure deficit and other climatic factors (i.e., temperature, precipitation, and radiation) negatively controlled EWUE. Compared to satellite-derived EWUE, we found that EWUEs derived from an ensemble of process-based carbon cycle models are overestimated in seven out of ten models, with an increasing trend of 0.11 g C mm−1decade−1(P< 0.001) for spatially averaged EWUE of the ensemble mean. The relationships between climatic factors and EWUE are partially misinterpreted in model estimates, especially with overstated CO2sensitivity and the opposite temperature effect. The fluctuating sensitivities to climate over time and the diminishing effect of CO2 fertilization on gross primary productivity (GPP) may partially explain the discrepancy observed between satellite-derived and model-based estimates of EWUE. Thus, this study calls for caution concerning model-based EWUE and aids in understanding permafrost-climate feedbacks and projections of carbon and water cycles.