Different phosphorus preferences among arbuscular and ectomycorrhizal trees in a subtropical forest

Phosphorus (P) is one of the most limiting elements for efficient plant growth and regeneration, coexisting plants are found to be able to partition soil P components through different types of mycorrhizal symbiosis. However, previous evidences were mostly based on artificial addition of different forms of P chemicals, there is still a lack of observational and experimental verifications on how tree species respond to soil P heterogeneity in natural soils. Herein, we conducted a field survey to investigate how spatial distribution of tree species with different types of mycorrhizal associations are related with soil P compositions. We found that arbuscular mycorrhizal (AM) trees tend to distribute in soils rich in inorganic P, while ectomycorrhizal (ECM) trees distribute in habitats with low inorganic P. We further established a shade-house experiment to evaluate how P availability of field soils affects seedling performance of AM and ECM trees. Biomass of AM seedlings was highest when grew in soil with the medium level of inorganic P, while ECM seedlings grown best in soil with the lowest inorganic P level. Seedling survival and mycorrhizal colonisation rates decreased, while specific root length and specific area of seedling roots increased, with increasing inorganic P concentrations. Using field soil with natural composition of P-forms and spatial heterogeneity, our findings confirmed the hypothesis that AM trees prefer inorganic P while ECM trees are able to utilise organic P in a more realistic setting, which regulated spatial distributions and promoted coexistence of subtropical tree species at local scale.