Microbial biomass, and dissolved organic carbon and nitrogen strongly affect soil respiration in different land uses: A case study at Three Gorges Reservoir Area, South China

In order to better understand the limiting factors and substrate affecting soil CO2 flux, we measured total organic carbon (TOC), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), dissolved organic carbon (DOC), and dissolved organic nitrogen (DON) from seven sites of four land-use types (1 vegetable field, 3 uplands, 2 orchards, 1 pine forest) of subtropical soils in Three Gorges Reservoir Area, China. Objectives were to (1) evaluate the separate and interactive relationship of TOC, MBC, MBN, DOC, and DON with soil CO2 flux, in addition to the relationship obtained by environmental variables (soil temperature and moisture), and (2) investigate the seasonal and annual CO2 fluxes from different land uses. Annual CO2 fluxes ranged from 5.4 to 9.5 Mg CO2 ha−1 year−1. Vegetable field had the highest CO2 emission, while pine forest had significantly lower CO2 emission than cultivated land uses. Different quantities of MBC and MBN significantly regulated the CO2 emission among different land uses, relatively weakly correlated with DOC, while not being correlated with DON. However, temporal fluctuations of CO2 flux were significantly regulated by MBC, MBN, DOC and DON, in one model of variation, in all land uses. But, when all the variables were included in the multiple stepwise regression analysis, different trend of dominancy was observed for soil temperature (two sites), MBC (one site), MBN (one site), DOC (two sites) and DON (one site). Our results indicate that (1) there can be a significant shift of microbial biomass with land-use change, which in turn, caused to shift in CO2 flux, and (2) apart from the soil temperature, microbial biomass and dissolved organic substances must be considered in a warming future as these can explain a major part of temporal variation of soil CO2 fluxes.