Canopy spectral cues affect plant growth and root-associated fungal communities of tree species with different mycorrhizal types

Soil fungi establish symbiotic associations with plant roots, which provide nutrients in exchange for photosynthate from the host. Despite the recognized importance of fungal symbiosis, how root-associated fungal communities respond to light qualities remains unclear. In this study, we conducted a novel spectral attenuation experiment involving seedlings of two temperate tree species, Quercus mongolica Fisch. ex Ledeb. (ectomycorrhizal [ECM]) and Acer mono Maxim. (arbuscular mycorrhizal [AM]). The experimental design incorporated five spectral treatments, including ambient full-spectrum as control and various attenuations of ultraviolet (UV) and visible light. We quantified tree growth and root traits, and profiled root-associated fungal communities through high-throughput sequencing. Results showed that plant growth and root traits varied depending on tree species and spectral treatments. Blue light significantly promoted total biomass of Q. mongolica, but reduced root exudative carbon, sugar and phenolics. In contrast, A. mono showed no spectral changes in biomass and had the lowest root exudative sugar and phenolics in control. Higher root exudative carbon and phenolics were observed in A. mono than in Q. mongolica. Root-associated fungal communities also showed distinct responses to spectral treatments and tree species. Sob's and Chao 1 indices of Q. mongolica fungal communities were significantly lower than those of A. mono under UV attenuation, and alterations in community structure were more pronounced in A. mono. These changes were strongly associated with root traits, particularly exudative carbon, sugar and total phenolics. Within fungal communities, Q. mongolica was dominated by ECM and saprotrophic fungi, and A. mono by AM and saprotrophic fungi. The relative abundance of ECM fungi in Q. mongolica and that of AM fungi in A. mono was lowest when UV-B radiation was attenuated. In total, these findings highlight the crucial role of root traits and their interaction with fungi when exploring plant adaptation to varying light environments.