Vegetos

Abstract

Carbon storage in Chinese grasslands comprises a substantial proportion of the carbon pool in worldwide grasslands and in China s terrestrial ecosystem. The objective of this study was to evaluate how carbon sequestration in the steppe ecosystem responds to grazing. Study sites with various grazing conditions were selected. The different grazing conditions included a non-grazing enclosure (NX) that had been fenced for 26 years, a light grazing site (LG) with occasional grazing at 3 sheep/ha in the winter, which represents approximately a 30% utilization of annual forage production for the last 30 years, and a heavy grazing site (HG) with continuous grazing at a constant stock rate of 3 sheep/ha during the entire year, which represents an 80% utilization of annual forage production. Vegetation carbon stocks (from aboveground live plants, standing dead plants, litter and roots) and soil carbon stocks were measured and compared among the three sites. The results demonstrated that different grazing intensities affected the total ecosystem carbon and the various grassland carbon pools. Compared with the nongrazed site, standing dead plant and litter carbon (C) decreased significantly in light grazing conditions, but light grazing did not significantly affect live plant C, total aboveground plant C, total root C (0–60 cm), and soil C (at 0-100-cm depths). Heavy grazing extensively reduced carbon in three pools, total aboveground plant C, subsoil C (at 60–100 cm), and total soil C (at 0–100 cm), but did not affect topsoil C (at 0–60 cm). The lack of an effect on topsoil C can be explained by a slight increase in root C (0–60 cm) and a higher ratio of root to vegetation C in the HG site. We propose that the decrease in subsoil C under heavy grazing is attributable to the organic carbon decomposition due to increased root C as a source of fresh carbon. Total ecosystem C decreased from 150.62 Mg C/ha in the NX site to 143.78 Mg C/ha in the LG site (a 4.5% decrease) and to 122.43 Mg C/ha in the HG site (an 18.7% decrease). Therefore, we conclude that light grazing is a sustainable management option for North China grasslands.