Resolving root and mycorrhizal strategies in response to soil phosphorus addition in forest ecosystems: a global meta-analysis.

Phosphorus (P) is a key and often scarce element for the growth and regeneration of trees. Formation of diversified roots and collaboration with different mycorrhizal fungi are crucial mechanisms for nutrient acquisition and species coexistence in forest ecosystems. However, how soil P enrichment modifies functional traits and mycorrhizal symbioses of absorptive tree roots remains unclear. We conducted a comprehensive meta-analysis of 601 observations from 108 studies to assess how fine root morphological, chemical, mycorrhizal, and enzymatic traits respond to soil P addition. We revealed that fine root length was generally promoted and mycorrhizal colonization reduced by P addition, with both effects intensifying along a gradient of P additions. P addition promoted root P concentration for both arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) trees, indicating an overall improvement in plant P status. However, AM trees showed stronger increases in root length, whereas ECM trees showed stronger increases in mycorrhizal fungal biomass. Our findings highlight the significant changes in fine root traits in response to soil P enrichment exhibited by AM and ECM trees, which may lead to different growth strategies between the two main mycorrhizal types and may contribute significantly to ecological niche partitioning and species coexistence under heterogeneous nutrient conditions.