The negative effect of Chinese fir (Cunninghamia lanceolata) monoculture plantations on soil physicochemical properties, microbial biomass, fungal communities, and enzymatic activities

Considerable natural or secondary forests have been converted to plantations in response to the growing needs for timber, paper, and fuel. Soil fungal communities are sensitive to ecosystem transformation and play an important role in aboveground-belowground linkages and biogeochemical cycling. However, the effect of forest conversion on fungal community structure and functions and driving mechanisms remains unclear. We investigated the response of soil fungal communities and the corresponding change in soil physicochemical biological properties and enzymatic activities to the natural broad-leaved forest (NBF) converted to the Chinese fir (Cunninghamia lanceolata) plantation (CFP) in subtropical China with ITS rRNA amplicon sequencing. Soil physicochemical properties, microbial biomass, fungal alpha diversities, and enzymatic activities decreased with forest conversion, including pH, soil water content, soil organic carbon, available phosphorus, total nitrogen, nitrate nitrogen, microbial biomass carbon and nitrogen, urease, protease, and acid phosphatase. Fungal community composition and structure were also strongly affected by forest conversion. Ascomycota had a higher read abundance in the NBF, but Basidiomycota showed a higher read abundance in the CFP. The read abundance of saprotroph and arbuscular mycorrhizal fungi increased with forest conversion, while that of ectomycorrhizal fungi decreased. Some fungal guilds—dung saprotrophs, lichenized fungi, endophytes, and lichen parasites—were even nearly lost in the CFP. These changes in fungal communities are all closely correlated to soil physicochemical properties, microbial biomass, and enzymatic activities. Overall, our study emphasizes the negative effect of the NBF conversion to the CFP on C, N, and P cycling mediated by fungi—and recommends replacing monoculture coniferous forests with mixed forests in reforestation to improve soil degradation.