Linking soil fungal community structure and function to soil organic carbon chemical composition in intensively managed subtropical bamboo forests

Abstract

Intensive forest management practices such as organic mulching and heavy fertilization can affect soil microbial composition and function, and soil organic carbon (SOC) forms. However, the linkage between soil microbial community composition and SOC forms is poorly understood in bamboo (Phyllostachys praecox) plantations under intensive management (mulching and fertilization). We examined the relationship between SOC (solid state 13C NMR) and fungal community compositions (real-time PCR, terminal restriction fragment length polymorphism, and clone library) in a chronosequence of intensively managed bamboo plantations (0, 1, 6, 10, and 15 years of stand age). The fungal community composition (internal transcribed spacer, ITS) and function (cellobiohydrolases, cbhI) and C forms in the top- (0–20) and subsoils (20–40 cm) were determined as fungi dominate cellulose (the main component of plant residues) decomposition in the soil. Soil fungal abundance (copy number of 18S rRNA) was positively correlated to O-alkyl C and aromatic C while negatively correlated to alkyl-C and carbonyl C concentrations. The alkyl C was the most influential SOC fraction on fungal community composition before intensive plantation management was applied, while O-alkyl C was the most influential C-form after more than 5 years of intensive management. The alkyl C, O-alkyl C, aromatic C and carbonyl C together explained 63.2 and 54.2% of the variations in total fungal composition in the top- and subsoils, respectively. Saprotrophic or cellulose-degrading species, mainly Mortierellales sp., Trichoderma sp. and Scheffersomyces sp., dominated the fungal community and the dominance increased with increasing plantation age (combined effects of stand age and duration of intensive management). The increased O-alkyl C concentration caused by increased plantation age explained shifts in the cbhI-containing community composition. Both the cbhI abundance and readily oxidizable C concentration increased with increasing plantation age in the topsoil but not in the subsoil. We conclude that in the intensively managed bamboo plantations changes in organic C forms were closely linked to changes in soil fungal community composition; such linkages have implications for soil nutrient cycling and C transformation in the plantation ecosystem.