Contrasting response of root traits of arbuscular mycorrhizal and ectomycorrhizal trees to phosphorus availability in subtropical forests

Aims: Soil phosphorus (P) availability regulates plant performance in many forests, but the mechanisms under-pinning these effects are unclear, which limits our ability to adequately understand plant community dynamics in these systems. Methods: We conducted a field survey and a soil P manipulation experiment in a subtropical forest to investigate how root functional traits, mycorrhizal colonisation and putative pathogen infection of arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) tree seedlings respond to gradients of soil P. Results: In the field, AM seedling roots were more heavily infected by pathogenic fungi than ECM seedling roots, while the opposite was seen for mycorrhizal colonisation. In the P manipulation experiment, mycorrhizal colonisation was enhanced and pathogenic infection was reduced when soil P availability was low. Root functional traits, including root-to-shoot ratio and root branching intensity showed opposite trends in their response to P availability between AM and ECM plants. Conclusions: Our findings suggest that AM and ECM seedlings have contrasting strategies to deal with P limitation: AM plants produce more fine roots, while ECM plants invest in mycorrhizal colonisation for P acquisition whilst also reducing the likelihood of pathogen infection. These contrasting strategies may regulate interspecific competition and contribute to the stable coexistence of different types of mycorrhizal plants.