An Estimate of Soil Carbon Stock of Grassland under Defferent Managements in Xilinguole, Inner Mongolia from 2000 to 2007
|School||Nanjing Agricultural College|
|Keywords||grassland management soil organic carbon Xilinguole League in Inner Mongolia|
As an important component of terrestrial ecosystem, grasslands are one of the most widespread vegetation types worldwide, covering nearly one-forth of the world’s land surface, and the soil carbon stocks amount to 20% of the global total, sograssland plays a significant role in climate change and global carbon cycle. The area of grassland in China is approximately 4×108ha, accounting for 12.5% of the total in world, distributed mainly in the western and northern areas, and the northern temperate steppe which almost covers 78% of the national grassland is the main grassland in China. As a result of overgrazing, unreasonable reclamation, over gathering and colleting, etc, the degenerate grassland area of the important pasture in northern China has increased from 39.7% in 1980s to 50.2% in 1990s, of which, areas of light, middle and heavy degenerate account for 57.3%,30.5% and 12.2% of the degenerate grassland respectively. Grassland degeneration leads to a different decreases in SOC storage.In the past ten years or more. China’s government has taken a set of grassland protection and construction projects to hold back degeneration, improve grassland ecosystem and enhance grassland productivity. Xilinguole League is one of important pastoral zones in the northern, measures such as fencing, improving and so on have been taken to protect the grassland eco-environment since the end of 20th century, good management practices not only restore the vegetation productivity of degraded grassland but also increase the SOC storage gradually. On the basis of grassland area with different managements and data sets of soil organic carbon (SOC) extracted from the literature, we estimated the changes in SOC of grassland in Xilinguole, Inner Mongolia Municipality from 2000 to 2007 by two approaches. One is the IPCC Tier 2, and the second is based on a transfer matrix of soil organic carbon under various managements. The objective is to elucidate the effects of grassland managements and provide support for making effective measures to increase carbon sink in grassland.The different managements have different influence to the SOC storage in grassland. The yearly increase amount of SOC for improving, mowing, enclosure were 0.83tC·hm-2·a-1 0.49tC·hm-2·a-1,0.63tC·hm·2·a-1. and the change rates of SOC were 2.0%,1.4%,2.4%. the SOC storage decreased with the grazing intensity increased, the annual SOC change for light grazing, medium grazing, heavy grazing were -0.15tC·hm-2·a-1,-0.45tC·hm-2·a-1-0.89tC·hm-2·a-1. and the change rates of SOC were -0.4%,-1.1%,-2.3%.The estimated results by the two approaches showed that SOC of grassland in the Xilinguole has increased by 20.85-29.80Tg, with an average rate of 2.61-3.72Tg a-1 over the period of 2000-2007. This increase is attributed to a substantial expansion of grassland enclosure. More than 80% of the increase was located in the counties of Dongwuzhumuqin, Xiwuzhumuqin, Sunitezuo, Suniteyou and Abaga, and Xilinhaote city. Correlation analysis indicated a good agreement of the estimated spatial changes in SOC using the two approaches, while it was approximately one third lower using the IPCC Tier 2 than that using the transfer matrix approach as the total amount was concerned. Nevertheless, the estimated annual SOC changes were not consistent between these two approaches. The annual increment of SOC in the first three years was greater than the last several years using the IPCC Tier 2, while the increment in the last five years was 1.4 times higher than the average of first three years using the transfer matrix approach. Moreover, the relative SOC stock change factors in the IPCC Tier 2 approach were much sensitive than the SOC density change factors in the transfer matrix approach to the estimates of SOCThe estimated results by IPCC Tier 2 and transfer matrix approach showed that the increasing amount of SOC for enclosure was the highest, followed by improving and mowing, the reduced area for light grazing led to the decrease of SOC by IPCC Tier 2 during 2000 to 2007. The total SOC increase in Dongwuzhumuqin county was the largest. while that was the smallest in Taipusi county. the total SOC change under different managements showed good comparability between IPCC Tier 2 and transfer matrix approach, the estimated results by the two methods indicated that the SOC storage increased for improving, mowing and enclosure(R2=0.97, p<0.001), but the results estimated by the former was 12 times more than that by the latter, while the SOC decreased for grazing(R2=0.90,p<0.001), and it underestimated 76 times as compared to the transfer matrix approach.