Impacts of nitrogen addition on plant species richness and abundance: A global meta-analysis
De Vries W
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Aim Experimental nitrogen (N) addition (fertilization) studies are commonly used to quantify the impacts of increased N inputs on plant biodiversity. However, as plant community responses can vary considerably among individual studies, there is a clear need to synthesize and generalize findings with meta-analytical approaches. Our goal was to quantify changes in species richness and abundance in plant communities in response to N addition across different environmental contexts, while controlling for different experimental designs. Location Global Time period Data range: 1985 – 2016; Publication years: 1990-2018 Major taxa studied Plants Methods We performed a meta-analysis of 115 experiments reported in 85 studies assessing the effects of N addition on terrestrial natural and semi-natural plant communities. We quantified local-scale changes in plant biodiversity in relation to N addition using four metrics: species richness (SR), individual species abundance (IA), mean species abundance (MSA) and geometric mean abundance (GMA). Results For all metrics, greater amounts of annual N addition resulted in larger declines in plant diversity. Additionally, MSA decreased more steeply with N that was applied in reduced (NH4+) rather than oxidised (NO3-) form. Species richness loss with increasing N amounts was found to be larger in warmer sites. Further, greater losses in species richness were found in sites with longer experimental duration, smaller plot sizes and lower soil cation exchange capacity (CEC). Finally, abundance reductions of individual species were larger for N-sensitive plant life-form types (legumes and non-vascular plants). Main conclusions N enrichment decreases both species richness and abundance of plants in N-addition experiments, but the magnitude of the response differs among biodiversity metrics and with the environmental and experimental context. This underlines the importance of integrating multiple dimensions of biodiversity as well as relevant modifying factors into assessments of biodiversity responses to global environmental change.