Drought and nitrogen enrichment could profoundly affect the productivity of semiarid ecosystems. However, how ecosystem productivity will respond to different drought scenarios, especially with a concurrent increase in nitrogen availability, is still poorly understood. Using data from a 4‐year field experiment conducted in a semiarid temperate steppe, we explored the responses of aboveground net primary productivity (ANPP) to different drought scenarios and nitrogen addition, and the underlying mechanisms linking soil properties, plant species richness, functional diversity (community‐weighted means of plant traits, functional dispersion) and phylogenetic diversity (net relatedness index) to ANPP. Our results showed that completely excluding precipitation in June (1‐month intense drought) and reducing half the precipitation amount from June to August (season‐long chronic drought) both significantly reduced ANPP, with the latter having a more negative impact on ANPP. However, reducing half of the precipitation frequency from June to August (precipitation redistribution) had no significant effect on ANPP. Nitrogen addition increased ANPP irrespective of drought scenarios. ANPP was primarily determined by soil moisture and nitrogen availability by regulating the community‐weighted means of plant height, rather than other aspects of plant diversity. Our findings suggest that precipitation amount is more important than precipitation redistribution in influencing the productivity of temperate steppe, and nitrogen supply could alleviate the adverse impacts of drought on grassland productivity. Our study advances the mechanistic understanding of how the temperate grassland responds to drought stress, and implies that management strategies to protect tall species in the community would be beneficial for maintaining the productivity and carbon sequestration of grassland ecosystems under climate drought.

中文翻译：

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添加氮可减轻干旱对温带草原植物生产力的不利影响


干旱和氮富集可能深刻影响半干旱生态系统的生产力。然而，生态系统生产力如何应对不同的干旱情景，尤其是氮肥利用率同时增加的情况，人们仍然知之甚少。利用在半干旱温带草原进行的四年田间实验的数据，我们探讨了地上净初级生产力（ANPP）对不同干旱情景和氮添加的响应，以及联系土壤性质、植物物种丰富度和功能多样性的潜在机制（植物性状的群落加权平均值、功能分散度）和 ANPP 的系统发育多样性（净相关性指数）。我们的结果表明，完全排除6月份的降水（1个月的严重干旱）和减少6月至8月降水量的一半（全季的慢性干旱）都会显着降低ANPP，后者对ANPP的负面影响更大。然而，6月至8月降水频率减少一半（降水重新分配）对ANPP没有显着影响。无论干旱情况如何，添加氮都会增加 ANPP。 ANPP 主要由土壤湿度和氮素有效性（通过调节植物高度的群落加权平均值）决定，而不是植物多样性的其他方面。我们的研究结果表明，降水量对温带草原生产力的影响比降水再分配更重要，施氮可以减轻干旱对草原生产力的不利影响。 我们的研究推进了对温带草原如何应对干旱胁迫的机制理解，并意味着保护群落中高大物种的管理策略将有利于在气候干旱下维持草原生态系统的生产力和碳固存。