Soil microbial community composition rather than litter quality is linked with soil organic carbon chemical composition in plantations in subtropical China

Native broadleaf plantations are increasingly being developed as an alternative to coniferous plantations. This study examined the relationships among litter carbon (C) quality, soil microbial community composition, and soil organic C (SOC) chemical properties in plantations and how they were affected by tree species. The solid-state C-13 nuclear magnetic resonance spectroscopy (NMR) technique was used to examine SOC chemical composition, and litter and fine root C quality in four plantations of native tree species (Pinus massoniana, Castanopsis hystrix, Michelia macclurei, and Mytilaria laosensis) in Pingxiang, Guangxi Zhuang Autonomous Region, in subtropical China. Soil microbial biomass C and nitrogen (N) were determined by the chloroform fumigation-extraction method and soil bacterial and fungal biomass were measured with the phospholipid fatty acid (PLFA) technique. The proportions of O-alkyl C, alkyl C, aromatic C, and carbonyl C in SOC and the alkyl/O-alkyl C ratio (A/O-A) in litter and fine root samples, soil microbial C and N, microbial C/N ratios, and the amount of PLFAs were significantly different among the four plantations of different species. SOC in the 0-10-cm layer had 43-49 % O-alkyl C, 24-34 % alkyl C, 14-17 % aromatic C, and 9-11 % carbonyl C in SOC. The microbial C/N ratio, the amount of total PLFAs, and bacterial and Gram-positive bacterial population sizes were linked to the proportion of alkyl C in SOC and the A/O-A ratio in soil. The proportion of alkyl C in SOC was not related to the proportion of alkyl C in litter or fine root samples. The microbial community composition rather than plant litter or fine root quality was linked to chemical composition of SOC in the studied subtropical plantations. Future research should place more emphasis on the processes involved in the formation of SOC and their association with the microbial community.