Responses of root- and soil-associated AM fungi to simulated nitrogen deposition, drought, and seasonal change in a subtropical Chinese fir plantation

Arbuscular mycorrhizal (AM) fungi play key roles in sustain tree productivity and forest ecosystem health. Here, tree root- and soil-inhabiting AM fungi were examined in a simulated atmospheric nitrogen deposition (nitrogen addition, N) and/or drought (i.e., precipitation exclusion, PE) field experiments in a Chinese fir plantation. The results showed that PE significantly reduced AM fungal intraradical colonization rate (IRCR) in summer. Nitrogen addition had no significant effect on AM fungal IRCR, hyphal and spore densities. However, season significantly affected the morphological structure of AM fungi. The direct effects of seasonal change, as well as the indirect effects through soil moisture, dissolved organic carbon (DOC) and microbial biomass phosphorus (MBP), resulted in higher AM fungal hyphal biomass (IRCR and extraradical hyphal density) observing in summer than in winter. Neither N nor PE exerted significant impacts on AM fungal diversity and community composition. However, AM fungal communities differed significantly between winter and summer. In winter, both root- and soil-associated AM fungal community composition significantly correlated with the ratio of microbial biomass carbon (MBC) and MBP. In summer, AM fungal communities appeared to be primarily associated with MBP and DOC. These findings highlight the importance of considering seasonal changes when evaluating the impacts of global change factors on AM fungi in plantation ecosystem.