Atmospheric nitrogen deposition affects forest plant and soil system carbon:nitrogen:phosphorus stoichiometric flexibility: A meta-analysis

Background: Nitrogen (N) deposition affects forest stoichiometric flexibility through changing soil nutrient availability to influence plant uptake. However, the effect of N deposition on the flexibility of carbon (C), N, and phosphorus (P) in forest plant-soil-microbe systems remains unclear. Methods: We conducted a meta-analysis based on 751 pairs of observations to evaluate the responses of plant, soil and microbial biomass C, N and P nutrients and stoichiometry to N addition in different N intensity (0-50, 50-100, >100 kg & sdot;ha(-1)& sdot;year(-1) of N), duration (0-5, >5 year), method (understory, canopy), and matter (ammonium N, nitrate N, organic N, mixed N). Results: N addition significantly increased plant N:P (leaf: 14.98%, root: 13.29%), plant C:P (leaf: 6.8%, root: 25.44%), soil N:P (13.94%), soil C:P (10.86%), microbial biomass N:P (23.58%), microbial biomass C:P (12.62%), but reduced plant C:N (leaf: 6.49%, root: 9.02%). Furthermore, plant C:N:P stoichiometry changed significantly under short-term N inputs, while soil and microorganisms changed drastically under high N addition. Canopy N addition primarily affected plant C:N:P stoichiometry through altering plant N content, while understory N inputs altered more by influencing soil C and P content. Organic N significantly influenced plant and soil C:N and C:P, while ammonia N changed plant N:P. Plant C:P and soil C:N were strongly correlated with mean annual precipitation (MAT), and the C:N:P stoichiometric flexibility in soil and plant under N addition connected with soil depth. Besides, N addition decoupled the correlations between soil microorganisms and the plant. Conclusions: N addition significantly increased the C:P and N:P in soil, plant, and microbial biomass, reducing plant C:N, and aggravated forest P limitations. Significantly, these impacts were contingent on climate types, soil layers, and N input forms. The findings enhance our comprehension of the plant-soil system nutrient cycling mechanisms in forest ecosystems and plant strategy responses to N deposition.