Extraradical hyphae alleviate nitrogen deposition‐induced phosphorus deficiency in ectomycorrhiza‐dominated forests

Summary The continuous imbalance between nitrogen (N) and phosphorus (P) deposition is expected to shift many ecosystems from N‐ to P limitation. Extraradical hyphae of ectomycorrhizal (ECM) fungi play important roles in plant nutrient acquisition under nutrient deficiency. However, whether and how ECM hyphae enhance soil P availability to alleviate N‐induced P deficiency remains unclear. We investigated the impacts of ECM hyphae on transformations among different soil P fractions and underlying mechanisms under N deposition in two ECM‐dominated forests. Ectomycorrhizal hyphae enhanced soil P availability under N addition by stimulating mineralization of organic P (Po) and desorption and solubilization of secondary mineral P, as indicated by N‐induced increase in positive hyphal effect on plant‐available P pool and negative hyphal effects on Po and secondary mineral P pools. Moreover, ECM hyphae increased soil phosphatase activity and abundance of microbial genes associated with Po mineralization and inorganic P solubilization, while decreasing concentrations of Fe/Al oxides. Our results suggest that ECM hyphae can alleviate N‐induced P deficiency in ECM‐dominated forests by regulating interactions between microbial and abiotic factors involved in soil P transformations. This advances our understanding of plant acclimation strategies via mediating plant–mycorrhiza interactions to sustain forest production and functional stability under changing environments.