Carbon input manipulation affects soil respiration and microbial community composition in a subtropical coniferous forest

We determined the effects of aboveground and belowground C inputs on soil CO2 efflux and microbial community composition by phospholipid fatty acids using aboveground litter addition or removal and root trenching in a subtropical forest in Southern China. From January 2011 to December 2011, soil respiration varied with the seasonal changes in soil temperature and water content, but its pattern was not altered by C input manipulation. The effects of C input manipulation on the temperature sensitivity of soil respiration was season-dependent, which were greater in the dormant season than in the growing season. Litter addition increased the soil respiration by 33% compared with the control, whereas litter removal decreased it by 22.6%. Root trenching decreased soil respiration by 20.4%. Aboveground litter decomposition, root and rhizosphere respiration, and mineral soil respiration contributed to 22.3%, 20.1%, and 57.6% of total soil CO2 efflux, respectively. We also found that increase in soil CO2 efflux induced by litter addition was 10.4% greater than decrease by litter removal. Litter removal increased 21.6% of the concentration of Gram-positive bacteria and decreased 32.8% of the bacteria to fungi ratio, compared with the control. Root trenching increased the concentrations of bacteria, fungi, and actinomycetes by 28.8%, 161.2% and 32.5%, respectively, but decreased the Gram-negative to Gram-positive bacteria and the bacteria to fungi ratios by 57.4% and 107.9%. C input treatment did not increase the Gram-positive bacteria but nor decreased the Gram-negative to Gram-positive bacteria ratio. The concentration of the 16:0 PLFA and the Gram-negative to Gram-positive bacteria ratio were significantly correlated with soil respiration. These results suggest that root C input has greater influence on soil microbial community composition than the aboveground litter C input.