Nitrogen addition induces microbial phosphorus limitations in bulk soil but not in rhizospheric soil: A global analysis

The increased nitrogen (N) deposition can regulate ecosystem stability by enhancing plant photosynthesis, elevating transpiration, acidifying soil, and altering microbial metabolic limitations. Higher N deposition can alleviate ecosystem-level N limitation, yet its impact on microbial phosphorus (P) limitations in both the bulk and rhizospheric soils remains debated. For this study, we conducted a global meta-analysis based on 372 paired bulk and rhizospheric soils observations derived from 46 field studies. We found that the responses of enzyme stoichiometries and microbial P limitations determined by vector model to N addition differed between bulk and rhizospheric soils. Specifically, N addition increased the enzymatic carbon:N ratio by 14 % in the bulk soil, but had no impact in the rhizospheric soil. Meanwhile, N addition increased available N:P ratio by 85 % in the bulk soil but no effect on the rhizospheric soil, and decreased the enzymatic N:P ratio by 24 % and 12 % in the bulk and rhizospheric soils, respectively. Microbial P limitations in the bulk soil also intensified, as reflected by a 4 % increase in the vector angle. Conversely, N addition did not lead to microbial P limitations in the rhizospheric soil. Furthermore, the response of vector angle in the bulk soil was negatively correlated with the response of soil organic carbon, which suggested that the intensified microbial P limitations induced by N deposition might accelerate its decomposition. This work provides insights into the predictive modeling of the relationships between microbial nutrient limitations and terrestrial carbon sinks under global N deposition.