Effect Of Enclosure On The Carbon Budget Of Stipa Grandis Communities In Inner Mongolia

Studying the carbon budget process of grassland ecosystem is one of the key contents to understand the global carbon cycle. Currently, the typical steppe region in Inner Mongolia is one of the areas that disturbed by human activities seriously. Over the years, overgrazing and unreasonable grassland development have led to a large area of grassland taking place different degree of degradation. In order to curb the trend of grassland degradation, the state has adopted a series of measures, among which the enclosure was most effective, and played an important role in promoting the restoration of degraded grassland.In order to elucidate the impact of enclosure on the carbon budget of grassland and the role of the enclosure in the restoration of degraded grassland, from July to August2010and from May to September2011we selected Stipa grandis communities with three different enclosed years (enclosed for6years,8years and31years respectively) and that unenclosed in the Xilin River basin of Inner Mongolia as study objects to investigate their community characteristics, the soil organic carbon (SOC) content, soil available nitrogen (SAN) content, soil available phosphorus (SAP) content, soil respiration rate in growing season and other soil properties (including soil moisture and soil mechanical composition). Our results showed that:(1) Enclosure promoted the increase of carbon stocks during restoration process of the degraded grassland, but increasing amount of soil, plant and litter was not equal with the order being soil carbon storage> underground root carbon storage> aboveground plant carbon storage> litter carbon storage. Compared with unenclosed Stipa grandis community, the communities with different enclosure years showed increased plants, litter and soil carbon stocks, and the root carbon storage was the largest while litter carbon reserves was the lowest.(2) Enclosure eliminated the interference of grazing on the soil of Stipa grandis community and made the soil be restored. The SOC content in the plots with different enclosure years was higher than that in unclosed plot, and in all the enclosed plots the SOC content in0-30cm soil layers all decreased with the soil depth increasing. Additionally, the SOC content in0-30cm soil layers increased significantly with the increase of enclosure years.(3) The soil nutrient content changed during the restoration process of degraded grassland. The contents of SAN and SAP in0-30cm soil layers in the enclosed plots were higher than that in unenclosed plot. In plots with different enclosure years, SAN content did not show a significant linear change with the increase the enclosure years. With the increase of soil depth in0-30cm, SAP content decreased in all the plots. No significant difference in SAP content was found among enclosed plots.(4) The soil respiration rate in enclosed plots was all higher than that in unenclosed plot. For all the plots, the soil respiration rate all increased firstly and then decreased, and the maximum value of soil respiration was all appeared in June and July. Additionally, the largest differences of soil respiration rate among the plots were all found in June and July.(5) In enclosed and unenclosed plots, the carbon budget in growing season showed as follows:the carbon fixation, emissions of soil respiration and the carbon sequestered were all larger in enclosed plots relative to unenclosed plot. With the increase of enclosure years, the plant carbon storage, soil carbon storage and carbon sequestered were all increased obviously.(6) The carbon sequestration potentials of degraded Stipa grandis grassland with different enclosure years were different. In the enclosed plots, the potential of soil carbon sequestration was greater than that of plant. After the grassland was taken to enclosure measures, the carbon sequestration potential of plants increased with the increase of the enclosure years, and underground root biomass had the largest carbon sequestration potential (167.627gC/m2) while the litter showed the lowest one (35.817gC/m2. With the increase of the enclosure years, the soil carbon sequestration potential in0-30cm soil layers increased with the soil depth increasing, but the carbon sequestration potential was different in different soil depth. Additionally, with the enclosure years increasing, the average annual soil carbon sequestered was first increase and then decrease.