Response of root- and soil-associated AM fungi to nitrogen addition and simulated drought in a Chinese fir plantation

Global change factors like atmospheric nitrogen (N) deposition and drought pose threats to forest ecosystem including soil microbial diversity. However, how arbuscular mycorrhizal (AM) fungi associated with tree respond to N deposition and drought remains largely unknown. Here root- and soil-inhabiting AM fungi were examined in a field experiment involving N addition and simulated drought (precipitation exclusion) in a Chinese fir (Cunninghamia lanceolata) plantation. The results showed that precipitation exclusion significantly reduced AM fungal intraradical colonization rate in summer, while N addition had no significant effect on AM fungal morphological traits of intraradical colonization rate, hyphal and spore densities. However, seasonal changes significantly affected AM fungal morphological traits, with higher values were observed in summer than in winter. Neither N addition nor drought significantly affected AM fungal diversity or community composition, but AM fungal communities exhibited pronounced seasonal differences. In winter, both root- and soil-associated AM fungal community composition significantly correlated with the ratio of microbial biomass carbon and phosphorus (MBC/MBP), while in summer AM fungal communities were primarily associated with MBP and DOC. These findings highlight the importance of accounting for interaction of N addition and drought, and seasonal response difference on AM fungi in subtropical forest ecosystems.