Influences Of Grassland Desertification On Soil Organic C And N In Northwestern Sichuan, China

Grassland desertification is one of the most serious environmental problems in our country. Ecological restoration of desertification grassland is one of most serious problems that should be solved in our country, which had received wide attention of scholars both at home and abroad at present. It is significance to know about the characteristics of SOC and N in different desertification grassland to explore the mechanism of grassland desertification and desertification grassland ecological restoration. Soil organic C (SOC) and soil nitrogen (N) were important factors to indicate the change of soil fertility and quality in desertification grassland with the development of desertification, but the researches on characteristics of SOC and N in the process of grassland desertification reported were mainly focused on arid and semi-arid areas, there is few data of that in semi-humid region. In addition, previous researches on SOC and N in desertification grassland were limited to the total of SOC and total nitrogen (TN), and there were lack of active fractions of C and different forms ofN.因此,本研究通过野外实地调查,以不同沙化程度草地为研究对象,调查了沙化草地植被群落信息特征,并采用分层采样方法,测定分析了0-100 cm土层Therefore, vegetation information in different degrees desertification grassland were investigated thro ugh the field investigation, and soil sample in 0-100 cm soil depth were got by stratified sampling method, dissolved organic C (DOC), labile organic C (LOC), microbial biomass C (MBC), and available N (AN), ammonium N (NH4+-N), nitrate N (NO3--N), microbial Biomass N (MBN), total acid hydrolysable N (THAN), acid solution of ammonium N (ASAN), amino sugar N (ASN), amino acid N (AAN) were determination of analyzed, the results showed that:(i) The biomass, community coverage, species and average height of community were decreased significantly with development of grassland desertification in the study area, compared to control with not desertification grassland (CTRL), aboveground biomass, underground biomass and community coverage, average height of community and species were reduced by 91.78%,94.65% and 91.78% respectively,71.68% and 83.33% in severe desertification grassland (SDG) (P<0.01); Soil particles in 0-100 cm soil layers presented a characteristics that sand content increased, and silt and clay content reduce variation, among them, the extremely severe desertification grassland are not desertification grassland soil sand content increased by 9.49%(P<0.05), silt and clay content decreased by 78.43% and 78.43%, respectively (P< 0.05).(ⅱ) Grassland desertification lead to SOC,DOC, LOC, MBC decreased significantly in 0-100 cm soil depth, and presented a characteristics as MBC> DOC>LOC>SOC, compared to the CTRL, the content of MBC, DOC, LOC, SOC were reduced by 76.43%, 74.89%,70.37% and 66.07%, respectively (P<0.01); The contents of SOC, DOC, LOC and MBC decreased most significantly between CTRL and light desertification grassland (LDG) with development of grassland desertification. In addition, in soil profile, the content of SOC, DOC, LOC and MBC were decreased most significantly in 0-20 cm soil depth, they decreased by 82.97%,85.99%,84.15% and 82.97%, respectively (P<0.01).(ⅲ) The content of soil N in 0-100 cm soil layer decreased significantly caused by desertification in Northwest Sichuan alpine grassland, compared to CTRL, the content of TN, AN, NH4+-N, NO3--N, MBN, THAN, AS AN, ASN and AAN decreased by73.95%, 77.72%,76.75%,79.77%,84.12%,79.53%,77.70%,68.93% and 79.53%, respectively (P<0.01); The contents of TN, AN, NH4+-N, NO3--N, MBN, THAN, ASAN, ASN and AAN decreased most significantly between CTRL and LDG with development of grassland desertification. In addition, in soil profile, the content of TN, AN, NH4+-N, NO3--N, MBN, THAN, ASAN, ASN and AAN decreased most significantly in 0-20 cm soil depth, they decreased by 86.43%,83.52%,82.11%,88.82%,91.77%,90.58%,91.44%, 87.77% and 91.01%, respectively (P<0.01).(iv) SOC, DOC, LOC, MBC and TN, AN, NH4+-N, NO3--N, MBN, THAN, ASAN, ASN and AAN were correlated significantly with development of desertification in Northwest Sichuan alpine grassland (P< 0.01), and the C/N increased gradually; SOC, DOC, LOC, MBC all had a negative correlation with sandy soil, and all had a positive correlation with silt, clay and ground vegetation coverage (P< 0.01), so did TN, AN, NH4+-N, NO3--N, MBN, THAN, ASAN, ASN and AAN. It indicated that silt, clay were erosion by wind and the decreased of community coverage were the two main factors that caused loss of SOC and N.