A Global Meta-analysis Reveals that Nitrogen Addition Alters Plant Nutrient Concentration and Resorption in Grassland Ecosystems

Knowledge of plant nutrient strategies is crucial for defining and predicting the patterns and mechanisms resulting from nitrogen (N) deposition. However, the impacts of N enrichment on plant nutrient strategies are unclear in global grasslands. We conducted a meta-analysis of 127 publications to synthesize the pathways underlying the responses of plant nutrient concentration and resorption to N addition across global grassland ecosystems. Our analysis indicated that N addition increased the N concentration in green and senesced leaves, the phosphorus (P) concentration in senesced leaves, and aboveground and belowground biomass by about 32%, 50%, 7%, 74%, and 19%, respectively. Meanwhile, it reduced N resorption efficiency (NRE) and P resorption efficiency (PRE) by about 9% and 6%, respectively. Nitrogen addition did not significantly affect green leaf P concentration. These responses were modulated by N application rates and humidity, and they differed among grassland types, plant groups, fertilizer types, and experimental durations. Nitrogen addition changed the relationship between N and P in green leaves and between NRE and PRE, but it did not alter the N:P ratio in senesced leaves. Our results suggest that N addition affects leaf nutrient concentrations and resorption in global grassland ecosystems, although such effects vary among grassland types and among plant functional groups. Nutrient resorption may be a critical pathway that mediates plant regulation of the coupled N:P balance. Changes in humidity due to climate change also mediate the response of plant nutrients to N addition and thereby affect the soil–plant nutrient cycles of grassland ecosystems under future N enrichment.