Abstract: Abstract Aims Phosphorus (P) is an essential nutrient for plant growth and a critical factor of determining forest productivity. Most terrestrial plants can form symbiotic associations with either arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi to enhance their phosphorus uptake. AM mycorrhiza and ECM mycorrhiza vary significantly in their P-absorption strategies, which impacts the P cycling in ecosystems. Understanding how soil P availability varies across the forests dominated by AM trees and ECM trees can be conductive to elucidating the mechanisms of productivity maintenance in subtropical forests and guiding forest nutrient management. Methods We established 35 forest plots across a natural gradient of ECM tree dominance in the Badagongshan Nature Reserve, Hunan Province. We measured the contents of four forms of soil bioavailable P (CaCl2-P, Enzyme-P, Citrate-P, HCl-P), and analyzed their relationships with ECM tree dominance. Correlation analyses were further employed to identify the key factors influencing soil bioavailable P contents. Important findings The results revealed that Enzyme-P content increased significantly with ECM tree dominance, while CaCl2-P, Citrate-P and HCl-P contents showed no significant correlations with ECM tree dominance. CaCl2-P content was positively correlated with leaf litter P content. Citrate-P and HCl-P contents were positively correlated with the contents of soil organic carbon, total nitrogen, and microbial biomass carbon. Enzyme-P content was positively correlated with the contents of soil organic carbon and dissolved organic carbon, and negatively correlated with soil pH. Additionally, soil acid phosphatase activity increased significantly with ECM tree dominance. In conclusion, ECM-dominated forests exhibit higher levels of enzyme-hydrolysable P and acid phosphatase activity, which can facilitate P solubilization through organic P mineralization, thereby promoting the rapid growth of ECM trees in subtropical forests.

Key words: mycorrhizal types, phosphorus, soil bioavailable phosphorus bioavailability, ECM tree dominance, acid phosphatase activity