Soil fungal community plays an important role in forest ecosystems, and forest secondary succession is a crucial driver of soil fungal community. However, the driving factors of fungal community and function during temperate forest succession and their potential impact on succession processes are poorly understood. In this study, we investigated the dynamics of the soil fungal community in three temperate forest secondary successional stages (shrublands, coniferous forests, and deciduous broadleaf forests) using high-throughput DNA sequencing coupled with functional prediction via the FUNGuild database. We found that fungal community richness, α-diversity, and evenness decreased significantly during the succession process. Soil available phosphorus and nitrate nitrogen decreased significantly after initial succession occurred, and redundancy analysis showed that both were significant predictors of soil fungal community structure. Among functional groups, fungal saprotrophs as well as pathotrophs represented by plant pathogens were significantly enriched in the early-successional stage, while fungal symbiotrophs represented by ectomycorrhiza were significantly increased in the late-successional stage. The abundance of both saprotroph and pathotroph fungal guilds was positively correlated with soil nitrate nitrogen and available phosphorus content. Ectomycorrhizal fungi were negatively correlated with nitrate nitrogen and available phosphorus content and positively correlated with ammonium nitrogen content. These results indicated that the dynamics of fungal community and function reflected the changes in nitrogen and phosphorus availability caused by the secondary succession of temperate forests. The fungal plant pathogen accumulated in the early-successional stage and ectomycorrhizal fungi accumulated in the late-successional stage may have a potential role in promoting forest succession. These findings contribute to a better understanding of the response of soil fungal communities to the secondary forest succession process and highlight the importance of fungal communities during temperate forest succession.

The soil samples were collected on 28 April 2021. There were three monodominant forest stands per forest type, each with a size of 100 × 100 m. Five individuals with similar diameter at breast high were chosen from each plot. Three soil subsamples were collected at a depth of 0–10 cm after litter removal, observing 1 m distance from the central tree in three directions at 120° angles. All five individual subsamples were homogenized to a single sample (Qu et al., 2020). Care was taken during tree selection to maintain at least a 10 m distance from non-target tree species, and each targeted tree was located farther than 20 m from the forest edge. A distance of at least 10 m was maintained between sampled trees to ensure spatial independence.

All samples were put on ice and transported back to the laboratory. After removing impurities (stones, roots), each sample was divided into three subsamples. (1) One subsample was immediately air-dried for determining soil pH, TN, total carbon (TC), total phosphorus (TP), total potassium (TK), soil organic carbon (SOC), available phosphorus (AP), and available potassium (AK). (2) A -20 ℃ storage subsample was used to analyze nitrate nitrogen (NO₃⁻-N) and ammonium nitrogen (NH₄⁺-N) within 2 weeks. (3) A -80 ℃ storage subsample was used to extract DNA.