Long‐Term Atmospheric Nitrogen Deposition Enhances Forest Production by Suppressing Microbial Competition for Phosphorus

ABSTRACT Ecological stoichiometry theory predicts that prolonged nitrogen (N) deposition exacerbates phosphorus (P) limitation in terrestrial primary production. However, this hypothesis remains untested using canopy N addition (CN) experiments that consider critical canopy processes. In a 10‐year CN and understory N addition (UN) experiment in P limited subtropical forests, CN unexpectedly increased plant biomass and P uptake while reducing soil microbial P, alleviating plant P limitation. A meta‐analysis of 151 published articles confirmed that CN‐induced increases in plant biomass and P uptake are widespread across forest ecosystems. Greater plant P uptake under CN was linked to higher fine root biomass, leaf transpiration rates, and P resorption efficiency. CN also stimulated soil acid phosphatase activity and phoC gene abundance, enhancing soil P availability for plants, resulting in reduced microbial and soil P pools compared with UN. These findings explain why high plant productivity persists in regions with high atmospheric N deposition and low P availability, with important implications for more accurately predicting plant productivity across forest ecosystems in a more realistic N deposition setting.