Ecological dynamics in acid rain-affected forests of subtropical China: unraveling the impacts of forest conversion, soil horizon and seasons on soil fungal communities
Tieshanping Forest Park is a pivotal region for studying the effect of acid rain on forests in subtropical China. In the 1980-1990s, to mitigate the impacts of acidic deposition on pure stands of Pinus massoniana (Pi), pine forests were converted to pure stands of Cinnamomum Camphora (Linn) Presl (Ci) and mixed stands (Pi_Ci). Between 2018-2019, we seasonally sampled both O and A soil horizons soil from these three forest types to explore the influence of forest conversion, soil depth, and sampling season on soil fungal communities. Horizon strongly influenced microbial biomass, with a threefold increase in O horizons, as compared to A horizons (p<0.001); likewise, fall and spring seasons also exhibited higher levels of biomass than was found in winter or summer, respectively. Forest types containing Ci contained higher fungal diversity than pure stands of Pi, with corresponding levels of diversity observed in O than A soil horizons. Fungal diversity varied seasonally and attenuated from spring to summer, as well as from fall to winter. The composition of soil fungal communities was structured by forest type, soil layer, and sampling season. Fungi from phylum Basidiomycota were dominant (40.83%) in Pi stands, whereas taxa from Ascomycota were most prevalent in both Pi_Ci and Ci stands. Fungal community structure clustered by forest type and soil layer. Pi hosts abundant ectomycorrhizal (ECM) fungi, acidophilic - or acid producing - species, and pathogens, while Ci harbored taxa such as Mortierella and Tolypocladium which may contribute to supporting plant resilience against soil acidification. Soil properties, such as total phosphorus and nitrate nitrogen, strongly correlated with fungal genera. Functional group composition varied with forest types, with Pi favoring ECM guilds, while Pi_Ci and Ci were dominated by fungal endophytes and decomposers. Seasonal variation in functional groups was evident, reflecting the intricate interplay between soil properties and fungal communities. This research provides valuable insights into the soil fungal dynamics in acidic soil, emphasizing the necessity for continuous, long-term monitoring to capture nuanced variations over time, especially in recovering forested systems.