Nitrogen deposition alleviates phosphorus-induced imbalances in soil enzyme stoichiometry

Soil extracellular enzymes are critical drivers of carbon (C) and nutrient cycling in terrestrial ecosystems. However, the effects of phosphorus (P) additions on soil enzyme activities and stoichiometries, particularly under varying nitrogen (N) addition regimes worldwide, are not well comprehended. Here, we conducted a meta-analysis based on 155 field studies across various ecosystems (forests, croplands and grasslands), which shows that P enrichment conditions enhances C-acquiring enzymes but has no effect on the enzymatic C:N ratio. P addition alone reduces P-acquiring enzymes by 14% without affecting N-acquiring enzymes. In contrast, P combined with N addition boosts N-acquiring enzymes by 21% while leaving P-acquiring enzymes unchanged. Notably, the combined effect of P and N addition on microbial C limitation (assessed via vector length) and enzymatic stoichiometries is less pronounced than that of P addition alone. Key drivers of these responses include mean annual precipitation, soil microbial biomass, and its stoichiometries. These results suggest that N addition mitigates the stoichiometric imbalance and microbial C limitation induced by P addition, potentially promoting soil organic C accumulation. Our findings emphasize the critical need to account for such interactive effects in models predicting soil biogeochemical cycles under future changes in global exogenous N and P inputs. Phosphorus addition alone reduces phosphorus-acquiring enzyme activities by 14%, while phosphorus combined with nitrogen addition boosts nitrogen-acquiring enzyme activities by 21%, according to a meta-analysis based on 155 field studies across various ecosystems.