Differential responses of plant-soil-microbe C:N:P stoichiometry to nitrogen addition in grassland ecosystems

Atmospheric nitrogen deposition, a major driver of global change, exerts profound effects on the biogeochemical cycling of carbon (C), nitrogen (N), and phosphorus (P), as well as their stoichiometric ratios (C:N:P) in grassland ecosystems. Here, we conducted a meta-analysis of 1168 observations from 83 published studies to quantitatively assess the impacts of N addition on the C:N:P stoichiometry of plants, soils, and microbes across global grasslands. Our results show that N addition significantly increased plant and SOC content, enhanced N content in plants, soils, and microbial biomass, and reduced C:N ratios in plant leaves and soils by 17.3% and 2.7%, respectively. In addition, N addition markedly elevated N:P ratios in plant leaves (32.2%), soils (9.3%), and microbial biomass (16.8%). These stoichiometric responses were strongly mediated by N input rates and experimental duration, but showed broadly consistent patterns across climatic contexts. Collectively, our findings provide new insights into how N deposition alters elemental cycling and stoichiometric balance in grassland ecosystems, improving the predictive accuracy of ecosystem models and informing management strategies to mitigate the impacts of increasing N deposition under global change • Nitrogen addition alters C:N:P stoichiometry in the plant-soil-microbe system. • Stoichiometric responses are strongly mediated by N input rate and duration. • Plants, soils, and microbes show different homeostatic responses to N addition.