Human‐induced global changes such as nitrogen (N) deposition, climatic warming and rainfall changes have been determined to be common drivers of current plant community dynamics. However, it is unclear if and how the individual and combined effects of these drivers differently influence plant diversity and its relationship with productivity at the global scale. Here, we performed meta‐analyses with data compiled from 133 articles, comprising >2000 effect sizes, to assess the individual and combined effects of N addition, warming and increased rainfall on plant diversity and its relationship with productivity (using aboveground biomass as a proxy). We found that N addition decreased species richness, Shannon–Wiener index (H′) and evenness, while it increased aboveground biomass. In contrast, warming and increased rainfall had no effect on diversity although both also increased aboveground biomass. The combined effects of N addition + warming and N addition + increased rainfall showed significant negative effects on plant diversity, with additive and synergistic interactions, respectively. Warming + increased rainfall did not influence plant diversity. Both the individual and combined effects on plant diversity were influenced by several moderator variables, with negative impacts of the magnitude and experimental duration on N addition effects and of latitude on N addition + warming effects. Importantly, our results showed that the greater the increase in plant productivity with long‐term N addition, the greater the decline in plant diversity, and vice versa, indicating that the commonly observed positive diversity–productivity relationship would be reduced under long‐term N addition. Our study provides new insights for the development of predictive models of plant diversity dynamics in response to multiple concurrent global change drivers, while also highlighting a consistent, strong negative effect of N addition, pointing to a clear need for reducing N deposition.

中文翻译：

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氮素添加，变暖和降雨增加对植物多样性的影响及其与生产力的关系

人为导致的全球变化，例如氮（N）沉积，气候变暖和降雨变化，已被确定为当前植物群落动态的常见驱动因素。但是，目前尚不清楚这些驱动因素的个体和综合作用是否以及如何影响全球范围内植物多样性及其与生产力的关系。在这里，我们使用从133篇文章中收集的数据进行了荟萃分析，包括> 2000种效应量，以评估氮素添加，变暖和降雨增加对植物多样性及其与生产力的关系的单独和综合影响（使用地上生物量作为替代）。我们发现氮的添加降低了物种丰富度，香农-维纳指数（H'）和均匀度，同时增加了地上生物量。相反，变暖和降雨增加对多样性没有影响，尽管二者也增加了地上生物量。氮添加+变暖和氮添加+降雨增加的综合效应显示出对植物多样性的显着负面影响，分别具有加性和协同作用。气候变暖+降雨增加并没有影响植物的多样性。对植物多样性的个体影响和综合影响都受到几个调节变量的影响，幅度和实验持续时间对氮添加效应的负面影响以及纬度对氮添加+升温效应的负面影响。重要的是，我们的结果表明，长期添加氮肥可使植物生产力的提高幅度越大，植物多样性的降低幅度就越大，反之亦然，表明长期添加氮会降低通常观察到的正多样性与生产力的关系。我们的研究为响应多种并发的全球变化动因而开发植物多样性动态预测模型提供了新见识，同时还强调了添加氮的持续，强烈的负面影响，这表明明显需要减少氮的沉积。