Human-induced global changes such as nitrogen (N) deposition, climatic warming, and increased rainfall have been determined to be common drivers of current plant community dynamics. While empirical studies and reviews have demonstrated the individual effects of these three global change drivers on biodiversity, our understanding of their combined effects at regional and global scales remains limited. More importantly, despite there being a general positive relationship between plant biodiversity and productivity, we know little about how global change drivers alter the biodiversity-productivity relationship. These ecological associations are key to our understanding of the global extinction crisis and ecosystem functioning. Here, we performed a meta-analysis with data compiled from 134 articles, comprising more than 2000 effect sizes to assess the individual and combined effects of N addition, warming, and increased rainfall on plant diversity and diversity-productivity relationship.
Results/Conclusions
We found that N addition oppositely affected plant diversity and productivity, with significant negative effects on species richness, Shannon-Wiener index (H'), and evenness and positive effects on aboveground biomass. The effects of N addition on plant diversity were further enhanced when combined with warming or increased rainfall. Neither warming and increased rainfall alone, nor their combination, showed significant overall effects on plant diversity, although both significantly increased aboveground biomass individually. Both the individual and combined effects of the assessed drivers were, however, significantly influenced by moderator variables such as ecosystem type, climate, and experimental duration. We detected negative effects of both the dose of N added and experimental duration on plant diversity, indicating that low doses of N added for long periods can cause diversity loss similar to that of high doses of N applied for short periods. More importantly, the negative effects of N addition on plant diversity and its positive effects on plant productivity both increased with experimental duration, indicating that the commonly observed positive relationship between plant diversity and biomass could be tempered, or even be reversed. Our study provides new insights, which can shape the development of ecological models designed to predict plant diversity under global change scenarios and aid management strategies for biodiversity conservation.