Influence Of Different Ecological Restoration Years On Desertified Grassland Vegetation,Soil Organic C And N In Northwest Sichuan,China

Currently, grassland desertification has become a global problem. China is one of the most serious countries affected by desertification. So, grassland desertification is a serious problem that needs to be solved immediately. Soil organic carbon and soil nitrogen are important factors that show soil biological properties and soil health quality. Researching into the variation characteristics of soil organic carbon, soil nitrogen and enzyme activities in the process of ecological restoration of sandy grassland can help to learn about the ecological environment effect of ecological restoration of sandy grassland and that is of great significance in effectiveness evaluation and regulating measures of ecological restoration as well. In this study, we selected the unrepaired desertified grassland and fence planting tamarisk years respectively 2,4,6 and 8 years of grassland desertification as research subjects to investigate the desertified grassland vegetation community characteristics through time and space substitution. And stratified sampling method combined with laboratory analysis was used to study the component content and its variation characteristics of soil organic carbon, soil nitrogen and microorganism in the 0-60 cm layer. The results showed that:（1） The vegetation height, coverage, density, diversity and biomass had different degrees of increase along with the extension of ecological restoration time of sandy grassland. After ecological restoration eight years, the average height, coverage and density of herbaceous vegetation rose up to 23 cm,87% and 684 ind/m2 respectively, and herbaceous vegetation richness index, Shannon-Wiener diversity index, pielous evenness index were 2.642,2.147,1.123 respectively, which were significantly higher than the unrepaired desertified grassland. Ecological restoration 2,4,6,8 years later, aboveground biomass of tamarisk were 46.75 kg/100 m2,77.69 kg/100 m2,117.31 kg/100 m2 and 171.48 kg/100 m2, which showed significant differences （p<0.05）. Herbaceous vegetation aboveground biomass were 156.2 g/m2 after ecological restoration eight years, which increased by 267.53% respectively compared with unrepaired desertified grassland. Variance analysis showed that the difference in aboveground biomass reached remarkable level （p<0.05） and that of the underground biomass reached extremely remarkable level （p<0.01）.（2） In the process of ecological restoration, the content of soil organic carbon （SOC）, dissolved organic carbon （DOC）, readily oxidation carbon （ROC）, microbial biomass carbon （MBC） in different ecological restoration soil layers increased by different degrees, with all these contents in the 0-20 cm soil layer changed most obviously. In the 0-20 cm soil layer, soil SOC, DOC, ROC, MBC content in different ecological restoration years reached extremely remarkable level （p<0.01）. SOC, DOC, ROC, MBC content in soil （0-20 cm） reached 6.14 g/kg,55.43 mg/kg,0.86 g/kg and 128.94 mg/kg after ecological restoration eight years, which were all significantly higher than the unrepaired desertified grassland （p<0.01）. SOC, DOC, ROC, MBC content in 20-40 cm and 40-60 cm soil layer also showed a gradual increase, but its rate of increase and the differences were less significant than 0-20 cm soil layer.（3） Soil total nitrogen （TN）, available nitrogen （AN）, nitrate nitrogen （N03--N）, ammonium nitrogen （NH₄⁺-N） and microbial biomass nitrogen （MBN） content increased with the increasing of ecological restoration years. After ecological restoration eight years, TN, AN, NO₃^--N, NH₄⁺-N, MBN content increased by 100.00%,50.73%,444.19%, 302.70% and 654.02% respectively, compared with unpaired desertified grassland. TN, AN, NO₃^--N, MBN content in 0-20 cm soil layer increased by a big margin, reaching extremely significant difference level （p<0.01）, and soil NH₄⁺-N reaching significant difference level （p<0.05）. It also showed a gradual increase in 20-40 cm and 40-60 cm soil layer, but its rate of increase and the differences were less significant compared to 0-20 cm soil layer.（4） The activity of soil urease, sucrase and protease increased with the ecological restoration age increased, and the difference in different soil layers reached remarkable level （p<0.05） or extremely remarkable level （p<0.0l）.（5） Vegetation community coverage and soil SOC, DOC, ROC, MBC, TN, AN, NO₃^--N, NH₄⁺-N, MBN showed a significant positive correlation （p<0.0l）. Vegetation community coverage had different effects on SOC, N in different soil layers. In 0-20 cm soil layer, soil SOC and N were influenced by vegetation community coverage most significantly. Soil SOC had significant （p<0.05） or extremely significant （p<0.01） positive correlation with N, so as to soil SOC and N with soil microbial quantity and enzyme activities.