Saprotrophic fungi buffer the adverse effects of soil acidification on the soil nutrient supply ability of Chinese fir (Cunninghamia lanceolata) plantations

Soil nutrient supply is critical in maintaining plantation productivity and sustainable management. However, long-term continuous planting can result in soil acidification, and the underlying mechanisms of how soil microorganisms maintain soil nutrient supply ability under the stress of soil acidification remain elusive. Here, we investigated soil physicochemical properties and assessed soil fertility levels in mature Chinese fir (Cunninghamia lanceolata) plantations (MatCFPs) and middle-aged Chinese fir plantations (MidCFPs). 16S and ITS rRNA amplicon sequencing were performed to examine the soil bacterial and fungal community structure. Compared with MidCFPs, the soil organic carbon, total nitrogen, total phosphorus, ammonium nitrogen, and available phosphorus contents in MatCFPs soil were significantly higher, thus significantly improving the soil fertility level of MatCFPs. Additionally, we observed a significant decrease in soil pH in MatCFPs compared to MidCFPs. Resulting soil acidification in MatCFPs not only decreased soil bacterial abundance and network stability but also limited bacterial functions related to nitrogen and carbon cycling. In contrast, compared with MidCFPs, fungal abundance and network stability increased in acidified MatCFP soils. Fungal abundance rather than bacterial abundance was positively correlated with the soil fertility level, and saprotrophic fungi were the main microbial driver of soil fertility, which explained the 21.4% of the variation in the soil fertility level. This study improves our understanding of the importance of saprotrophic fungi in maintaining soil nutrient supply ability under the adverse effect of soil acidification and provides insight into sustainable plantation management.