Complementary foraging of roots and mycorrhizal fungi among nutrient patch types in four subtropical monospecific broadleaved tree plantations

Foraging in soil nutrient-rich patches is a key nutrient acquisition strategy for plants. However, how arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) trees integrate root and mycorrhizal fungal responses in exploring different nutrient patches is poorly understood, especially in generally phosphorus-limited subtropical forests. We established five nutrient patch treatments (control; nitrogen addition; phosphorus addition; nitrogen + phosphorus addition; and organic residue addition) using ingrowth root bags in monoculture plantations of four subtropical tree species (two AM and two EM (Castanopsis)) to investigate the foraging responses of absorptive roots and mycorrhizal fungi. Compared to control patches, neither roots nor mycorrhizal fungi of AM and EM trees showed significant proliferative responses in nitrogen addition patches. In phosphorus addition and nitrogen + phosphorus addition patches, AM trees showed significant proliferation for mycorrhizal fungi only, while EM trees showed significant proliferation for roots only. In organic residue addition patches, however, AM trees showed significant proliferation only for roots, while EM trees showed significant proliferation only for mycorrhizal fungi. Our results highlight that foraging strategies of roots and mycorrhizal fungi are complementary among nutrient patch types and between AM and EM trees. Predicting belowground nutrient foraging strategies requires integrating information on mycorrhizal and nutrient patch types, including potential limiting nutrients.