Responses of soil respiration to vegetation type conversion in south hilly red soil based on main components

Abstract: Soil respiration is one of the important parts of carbon cycling in terrestrial ecosystems. Because of strong soil and water conservation and ecological construction, the vegetation type conversion was very common in south red soil hilly. Studying the effects of vegetation type conversion on soil respiration and its key components, could help us not only well understand the internal mechanism of soil respiration and carbon cycle, but also scientifically evaluate the role and contribution of soil and water conservation to climate change. This paper investigated the changes of soil respiration rates for one year when eroded bare land was converted to Paspalum notatum Flugge grassland, Herbals citrus orchards and Pinus elliottii forest, respectively, using a LI-8100A automated soil CO2 flux system in Jiangxi eco-technology garden for soil and water conservation, including the separation of soil total respiration rate (Rs) and soil heterotrophic respiration rate (Rh), and their seasonal patterns and influencing factors. It showed that soil temperature, soil moisture and monthly soil CO2 emission rate generally fluctuated in different vegetation types during the study period. Both Rs and Rh displayed obvious seasonal pattern being high in summer and low in winter across the observed period in 4 vegetation types, with the highest fluxes observed in August or September and the lowest fluxes in January. Vegetation type conversion didn't change the seasonal pattern of soil respiration rates. Soil temperature at 5 cm depth had significant effect on the change dynamics of soil respiration rates, but soil moisture did not. Soil temperature at 5 cm depth could explain 83.3% and 86.0% of the variations in Rs and Rh. With the conversion from bare land to grassland, orchard and forest land, Rs was more sensitive to the change of soil temperature at 5 cm depth, and values of temperature sensitivity coefficient changed from 1.86 to 2.20, 2.72 and 2.75, respectively. The average proportions of Rh to Rs were 75%, 73% and 69% in grassland, orchard and forest, respectively, and there were no significant differences among the 3 vegetation types (P>0.05), which showed similar single-peak curves of change dynamics with the maximum of 100% in winter and the minimum of 50% in summer. In addition, the proportion of Rh to Rs decreased with the increase of Rs, and there were logarithmic relationships between the proportion and Rs (P<0.001). During the observation period, the mean values of Rs were 1.09, 3.15, 2.34 and 1.65 μmol/(m2·s) (CO2 emission amount) in bare land, grassland, orchard and forest land, respectively, which showed significant difference between bare land and grassland (P<0.05). The mean values of Rh were 1.09, 2.13, 1.51 and 1.04 μmol/(m2·s) (CO2 emission amount) in bare land, grassland, orchard and forest land, respectively, which showed significant difference between grassland and bare land, and between grassland and forest land (P<0.05). With the conversion from bare land to grassland, orchard and forest, the contents of total organic carbon, dissolved organic carbon and microbial biomass carbon of surface soil (0-20 cm) all increased, which would bring a better living environment for soil microbe. The change of soil respiration under vegetation type conversion would be caused by the combination of soil temperature and soil organic carbon (both the quantity and the quality) change. Vegetation type was an important influencing factor of soil respiration in the scale of region or ecosystem.