Effects of grazing and experimental warming on DOC concentrations in the soil solution on the Qinghai-Tibet plateau

Little information is available about the effects of global warming and land management on dissolved organic carbon (DOC) concentration in soil solution in the field. Here, for the first time, we used a free-air temperature enhancement (FATE) system in a controlled warming-grazing experiment in 2006 and 2007 to test the hypothesis that grazing modifies the response of soil solution DOC concentration to experimental warming. Warming with no-grazing (WNG) significantly increased the average soil solution DOC concentration to 40 cm soil depth by 14.1 and 17.2% compared with no-warming with no-grazing (NWNG) in 2006 and 2007 respectively based on 1.3-1.4 °C soil temperature increase. However, the lack of significant differences among warming with grazing (WG), no-warming with grazing (NWG) and NWNG indicate that moderate grazing modified the effect of warming on DOC concentration in the soil solution. The effect of grazing on DOC concentration in the soil solution varied with sampling date and soil depth. Generally, the direct contribution of soil temperature and soil moisture to variation of DOC concentration in the soil solution was small. Positive correlations were observed between soil solution DOC concentration in the surface soil and standing death quality and belowground biomass. The Lignin:N ratio in the standing death and belowground biomass at 10 cm soil depth explained 60% of the variation of mean DOC concentration at 10 cm soil depth. Soil moisture and belowground biomass explained 79% of the variation of the mean soil solution DOC concentration to 40 cm soil depth in 2007.