| Land-use change is the most universal and direct factors that has great effect on natural ecosystem. Change of Land-use can change the reflectivity of earth's surface and influence the diversity and production of vegetation, and then lead to the dynamic of soil carbon pool. Therefore,accurately assessment the effect of land-use change on the dynamics of grassland ecosystem carbon stocks and its components is important, and it will be contribute to predict the feedback relationship between the global climate change and the grassland ecosystem and sustainable use of grassland resources. However, the recent studies mostly focused on the dynamics of soil organic carbon in the study of soil carbon, while the dynamics of soil inorganic carbon is widely ignored,especially in the arid and semi arid areas, where soil inorganic carbon is much higher than soil organic carbon. This paper study the effect of cultivation on the soil carbon storage, soil inorganic carbon storage and soil organic carbon storage at 0-100 cm depth using two calculation methods of equivalent soil depth and equivalent soil mass method, and discussing correlation relationship between soil physical and chemical indicators(p H, conductivity and density) and soil organic carbon and inorganic carbon content using a a cultivation chronosequence that consisted of one grassland and four croplands for cultivation 1, 7, 17 and 24 years in Songnen Plain. Results showed that:Long-term cultivation decreased the content of SOC and increased the content of SIC.Compared with grassland, the content of SOC in 0-100 cm depth decreased 10.43%, 17.26%,5.95% and 11.22% for Crop-1Y, Crop-7Y, Crop-17 Y and Crop-24 Y, respectively, while the content of SIC in 0-100 cm depth increased 27%, 30.3%, 23.77% and 28.81% for Crop-1Y,Crop-7Y, Crop-17 Y and Crop-24 Y, respectively. The results obtained by equivalent soil depth method showed that SOC stock in the 0-100 cm depth decreased rapidly with a loss rate of 3.63 Mg C ha-1 yr-1 after conversion from grassland to cropland, while SIC stock in the 0-100 cm depth increased rapidly with a sequestrated rate of 0.53 Mg C ha-1 yr-1. Compared with the grassland,SOC stock in 0-100 cm depth decreased by 8.6, 11.4, 14.1, and 15.4 Mg C ha-1 for Crop-1Y,Crop-7Y, Crop-17 Y, and Crop-24 Y, respectively, while SIC stock at 0-100 cm depth measured increased by 12.9, 20.5, 4.7, and 6.8 Mg C ha-1 for Crop-1Y, Crop-7Y, Crop-17 Y, and Crop-24 Y,respectively. Due to the influence of SOC and SIC, the change trend of STC stock is increases at first and decreases afterwards.Results obtained by equivalent soil mass method showed that the effect of grassland cultivation on SOC stock in the 0-100 cm depth is very little, however the effect of grassland cultivation on SIC stock in the 0-100 cm depth is much higher. Compared with the grassland,although SOC stock in the 0-100 cm depth decreased by 6.78, 3.98 and 1.04 Mg C ha-1 forCrop-1Y, Crop-17 Y, and Crop-24 Y, respectively, but there is no significant differences between the treatments. SIC stock increased by 38.63, 30.8, 31.82 and 44.31 Mg C ha-1 for Crop-1Y,Crop-7Y, Crop-17 Y, and Crop-24 Y, respectively, after cultivation, and lead to a higher soil inorganic carbon stock found in cropland. The increase of SIC stock offset the decline of SOC stock, and leads to the STC stock increases continuously with a sequestrated rate of 7.30 Mg C ha-1 yr-1.The stock of soil carbon pool obtained by equivalent soil mass method is higher than the stock obtained by equivalent soil depth method. Compared with results of equivalent soil depth method,SOC stock in the 0-100 cm depth increased by 11.4, 4.7, 10.2 and 14.4 Mg C ha-1 for Crop-1Y,Crop-7Y, Crop-17 Y, and Crop-24 Y, respectively, and SIC stock in the 0-100 cm depth increased by25.8, 10.4, 27.2 and 37.6 Mg C ha-1 for Crop-1Y, Crop-7Y, Crop-17 Y, and Crop-24 Y, respectively.At the same time, the change rate of soil carbon pool also has obvious change. Compared with results of equivalent soil depth method, the loss rate of SOC stock in the 0-100 cm depth decreased2.75 Mg C ha-1 yr-1 using equivalent soil mass, while the sequestration rate of SIC stock in the0-100 cm depth increased 7.65 Mg C ha-1 yr-1. The change of soil bulk density is the main reason for the different results using two methods of estimation.The main factors for the changes of SOC and SIC content were soil bulk density and soil electrical conductivity. Results in our study showed that SOC content have significant negative correction with soil bulk density and soil electrical conductivity(P<0.001), and the correction between SOC and soil p H was not significant. However, SIC content has significant positive relationship with electrical conductivity and soil p H and bulk density(P<0.05). |
PDF Full Text Request