[Influences of grazing and exclosure on carbon sequestration in degraded sandy grassland, Inner Mongolia, north China].

Very little is known about the effects of continuous grazing and exclosure on carbon sequestration in semi-arid sandy grassland of North China. Soil-plant system carbon in representative degraded sandy grassland in Horqin sandy steppe (N42 degrees 58', E 120 degrees 42') was measured. Three situations were compared: continuous grazing (CG), exclosure for 5 years (5EX) and exclosure for 10 years (10EX). Ground cover increased from the CG (35%) to the 5EX (63%) and to the 10EX (81%), and accordingly soil organic carbon and total plant components carbon increased from the CG (493 g.m-2 and 95 g.m-2) to the 5EX (524 g.m-2 and 146 g.m-2) and to the 10EX (584 g.m-2 and 309 g.m-2). In terms of the distribution of carbon in plant-soil system, 65.3%, 78.2% and 83.9% of plant-soil carbon was in soils at 0-15 cm in the 10EX site, in the 5EX site and in the CG site, respectively. The results suggested that continuous grazing in the erosion-prone sandy grassland was very detrimental to vegetation, soil and surrounding environment. Under exclosure conditions, vegetation restoration and litter accumulation not only effectively protected soil from loss through wind erosion, but also significantly increased plant-soil system carbon storage, and thus sequestration of atmospheric carbon. However, the recycling of aboveground plant carbon to the soil was restricted when grazing was excluded and a large part of carbon sequestrated was immobilized in plant litter accumulating on the soil surface. Further research on time scale for exclosure is needed. It is concluded that the degraded sandy grassland could contribute to significant carbon sequestration with the implementation of protecting practices.