Extreme drought decreases aboveground net primary production (ANPP) in most grasslands, but the magnitude of ANPP reductions varies especially in C₃-dominated grasslands. Because the mechanisms underlying such differential ecosystem responses to drought are not well resolved, we experimentally imposed an extreme 4-yr drought (2015–2018) in two C₃ grasslands that differed in aridity. These sites had similar annual precipitation and dominant grass species (Leymus chinensis) but different annual temperatures and thus water availability. Drought treatments differentially affected these two semiarid grasslands, with ANPP of the drier site reduced more than at the wetter site. Structural equation modeling revealed that community-weighted means for some traits modified relationships between soil moisture and ANPP, often due to intraspecific variation. Specifically, drought reduced community mean plant height at both sites, resulting in a reduction in ANPP beyond that attributable to reduced soil moisture alone. Higher community mean leaf carbon content enhanced the negative effects of drought on ANPP at the drier site, and ANPP–soil-moisture relationships were influenced by soil C:N ratio at the wetter site. Importantly, neither species richness nor functional dispersion were significantly correlated with ANPP at either site. Overall, as expected, soil moisture was a dominant, direct driver of ANPP response to drought, but differential sensitivity to drought in these two grasslands was also related to soil fertility and plant traits.

中文翻译：

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C3草原极端干旱条件下植物性状和土壤肥力介导生产力损失

极端干旱降低了大多数草原的地上净初级生产力 (ANPP)，但 ANPP 减少的幅度各不相同，尤其是在 C ₃主导的草原中。由于这种不同的生态系统对干旱的反应机制尚未得到很好的解决，我们通过实验在两个干旱程度不同的C ₃草原上实施了极端 4 年干旱（2015-2018）。这些地点的年降水量和优势草种（羊草）相似) 但年温不同，因此可用水量不同。干旱处理对这两个半干旱草原的影响不同，干燥地点的 ANPP 比湿润地点减少得更多。结构方程模型显示，某些性状的群落加权平均值改变了土壤水分和 ANPP 之间的关系，这通常是由于种内变异。具体而言，干旱降低了两个地点的群落平均植物高度，导致 ANPP 的降低超出了单独由于土壤水分降低所致的降低。较高的群落平均叶碳含量增强了干旱对干旱地区 ANPP 的负面影响，而 ANPP-土壤-水分关系受湿润地区土壤碳氮比的影响。重要的，在任一地点，物种丰富度和功能分散与 ANPP 均无显着相关性。总体而言，正如预期的那样，土壤水分是 ANPP 对干旱响应的主要直接驱动因素，但这两个草原对干旱的不同敏感性也与土壤肥力和植物性状有关。