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.
Keywords: canopy interaction; canopy nitrogen addition; meta‐analysis; microbial phosphorus competition; phosphorus cycle; plant productivity.
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