Response of carbohydrate-degrading enzymes and microorganisms to land use change in the southeastern Qinghai-Tibetan Plateau, China

Land use change alters the soil carbon (C) cycle, but it is unclear how change in land use modifies the function and composition of the microbial communities involved in soil C cycling. In this research, we examined the impact of land use change on soil C fractions, C-degrading enzymes, carbohydrate-active enzymes (CAZyme) and composition of microbial community in the southeastern Qinghai-Tibet Plateau of China. We collected surface soils (0–20 cm) from seven sites that simultaneously included four land uses: farmland (FL), natural forest (NF), shrubland (SL) and artificial forest (AF). We determined soil physicochemical properties and performed metagenomic analysis to determine the microbial community composition and CAZyme genes. The results showed that soil C fractions were significantly decreased by 19–55 % when NF was converted to AF, SL and FL due to a decline in litter inputs (p < 0.05). Similarly, C-degrading enzymes significantly declined after NF converted to other land uses (p < 0.05). Moreover, changes in land use significantly affected the soil microbial composition (p < 0.05). In NF, the relative abundances of Proteobacteria, Candidatus Rokuobacteria and Verrucomicrobia were higher compared to FL and SL. Conversely, FL and SL had a significantly higher abundance of Actinobacteria, Acidobacteria, Chloroflexi, and Gemmatimonadetes phyla than NF soil. Furthermore, CAZyme genes were mainly derived from three bacterial phyla: Actinobacteria, Acidobacteria and Proteobacteria. The abundance of CAZyme genes such as glycosyl transferases and carbohydrate esterase were significantly higher in NF, while glycoside hydrolases, carbohydrate-binding modules and polysaccharide lyases genes were significantly higher in FL (p < 0.05). Changes in relative abundances of microbial marker genes, genes coding C-degrading enzymes and CAZyme genes were mainly linked to changes in soil properties, such as soil C fractions, total nitrogen, moisture content, microbial biomass nitrogen, bulk density and pH. Overall, our study provides an in-depth insight into the responses of C-cycling microorganisms and functional genes to land use changes.