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.

铁山坪森林公园是中国亚热带地区研究酸雨对森林影响的关键区域。20世纪80至90年代，为缓解酸沉降对马尾松（Pinus massoniana，简称Pi）纯林的负面影响，研究人员将该区域的松林改造为香樟（Cinnamomum Camphora (Linn) Presl，简称Ci）纯林以及马尾松-香樟混交林（Pi_Ci）。2018至2019年间，研究团队对这三种林型的O层与A层土壤开展了季节性采样，以探究林分改造、土壤深度以及采样季节对土壤真菌群落的影响。土壤发生层对微生物生物量具有显著影响：O层的微生物生物量较A层提升三倍（P<0.001）；同样，秋季与春季的微生物生物量也分别高于冬季与夏季。含香樟（Ci）的林分其真菌多样性高于马尾松（Pi）纯林，且O层土壤的真菌多样性水平同样高于A层。真菌多样性随季节发生变化，从春季到夏季、秋季到冬季均呈现下降趋势。土壤真菌群落的组成结构受林分类型、土壤层次以及采样季节的调控。马尾松（Pi）纯林中的优势真菌类群为担子菌门（Basidiomycota），占比达40.83%；而马尾松-香樟混交林（Pi_Ci）与香樟（Ci）纯林的优势类群则为子囊菌门（Ascomycota）。真菌群落结构按照林分类型与土壤层次发生聚类分布。马尾松（Pi）纯林富集大量外生菌根（ectomycorrhizal，ECM）真菌、嗜酸（或产酸）物种以及病原菌；而香樟（Ci）纯林则包含被孢霉属（Mortierella）与弯颈霉属（Tolypocladium）等类群，这些类群可能有助于提升植物对抗土壤酸化的抗逆能力。土壤总磷、硝态氮等理化性质与真菌属类群存在显著相关性。真菌功能群组成随林分类型而异：马尾松（Pi）纯林以外生菌根（ECM）功能群为主，而马尾松-香樟混交林（Pi_Ci）与香樟（Ci）纯林则以真菌内生菌与腐生分解者占主导。功能群组成存在显著的季节变化，反映了土壤理化性质与真菌群落之间复杂的相互作用。本研究为酸性土壤中的真菌群落动态提供了宝贵的研究视角，同时强调了开展长期连续监测的必要性，以捕捉随时间推移产生的细微变化，尤其是在森林恢复系统中。