Intensive clear cutting of natural forests and conversion to monoculture plantations are ongoing worldwide, leading to degradation of soil quality and microbial functions. Here, we compared soil quality index (SQI) and fungal community in a natural forest (Forest) and four 5-year-old monoculture plantations, including Camellia oleifera (Oil), Amygdalus persica (Peach), Myrica rubra (Berry) and Cunninghamia lanceolata (Fir), in a subtropical region of China. After conversion, soil pH rose up to 0.31, but organic carbon, total nitrogen, sucrase, acid protease, glutaminase and phosphatase activities decreased by 83%, 59%, 43%, 31%, 64%, 66% and 77%, respectively, in the plantations. Correspondingly, the SQI dropped by 65%. High-throughput sequencing of the ITS1 region demonstrated an increase in α-diversity and a striking difference in β-diversity following conversion. Changes in the dominant fungal taxa following forest conversion to plantations was interpreted by Grime’s C-S-R life history framework. Conversion increased the fungal groups with stress-tolerant (S) and ruderal (R) strategies - mainly copiotrophic saprophytes, such as Ascomycota and Zygomycota, but decreased the fungal groups with competitor (C) strategies - mainly oligotrophic saprophytes and mycorrhizal fungi, such as Basidiomycota. Genera affiliated to those phyla including Pseudophialophora, Rhytisma increased, but Russula decreased. Redundancy analysis and structural equation modeling indicated that the diversity and composition of fungal communities changed with soil quality degradation, which were mainly driven by increased soil pH, decreased available carbon and nutrients (N, P), and related enzymes activities.

Understanding the contributions of autotrophic respiration (Ra) and heterotrophic respiration (Rh) to total soil respiration (Rs) is necessary for accurate prediction of global carbon balance and net ecosystem production under environmental change. In this research, annual Rs and Rh and estimated were investigated by using a root trenching experiment in a Camphor tree (Cinnamomum camphora) forest in subtropical China for two years to qualify the relative contribution of Ra and Rh components to Rs, and to determine the environmental factors that control the seasonal changes in Ra, Rh and Rs. The results showed that annual mean Rs was 405 ± 219 gC m-2 year-1 in the studied forests, of which Rh and Ra were 240 ± 120 gC m-2 year-1 and 164 ±102 gC m-2 year-1, respectively. The contribution of Rh to Rs averaged 58.1%, ranging from 45 to 81%. The seasonal changes in Rs and Rh were highly correlated with soil temperature, but not to soil water content. Our results suggest microbial community and activity make a primary contribution to carbon flux released from soil to atmosphere in the studied forest ecosystems.