Sources And Stability Of Organic Carbon And Nitrogen In Soil Aggregates As Affected By Re-vegetation In The Loess Plateau

The Loess Plateau is an important ecological fragile area in China,and soil erosion and ecosystem degradation are serious.After nearly 50 years of vegetation restoration,the eco-environment was improved.With the control of soil erosion,the soil effect of vegetation restoration and the function of carbon sink of re-vegetated soil are becoming the urgent scientific problems to be recognized in the ecological environment construction of this area.This study aimed at the re-vegetated soil of Loess Plateau and analyzed the distribution characteristics of soil and aggregate carbon and nitrogen stable isotope distribution and identification of carbon and nitrogen sources,to obtain the contents of carbon and nitrogen deprived from forest or cropland in soil and aggregates.In order to reveal the relationship between re-vegetation ages,soil depth,soil texture and aggregates and the dynamic changes of soil organic carbon and total nitrogen.This study can provide a theoretical foundation to evaluate accurately the function and sustainability of soil carbon sequestration of re-vegetation.And it can also contribute to understanding the terrestrial ecosystem carbon and nitrogen cycle which dominated by soil organic carbon and nitrogen cycling.The main conclusions are as follows:?1?Re-vegetation can decrease the natural abundance of soil?¹³C and?¹⁵N in the 0-10 cm and 10-20 cm soil layer,but the effect differed with re-vegetation age.Re-vegetation can increase the concentrations of soil organic carbon and total nitrogen deprived from forest and both with the increase of vegetation restoration years significantly increased.The changes of soil organic carbon and total nitrogen deprived from forest and cropland were different with sites,and the difference in 0-10cm soil layer is more obvious.The results show that,with the change from fine soils to coarse soils,the content of organic carbon and total nitrogen in 0-10 cm soil depth deprived from forest decreased.?2?Re-vegetation can decrease the natural abundance of soil?¹³C and?¹⁵N in the 0-10 cm and 10-20 cm soil layer in aggregates,and both with the increase of vegetation restoration years significantly decreased.The results show that,with the soil texture from fine soils to coarse,the?¹³C and?¹⁵N natural abundance in macroaggregates and microaggregates increased,while the content of organic carbon and total nitrogen in macroaggregates and microaggregates deprived from forest decreased.As the soil texture from fine soils to coarse,the difference of carbon and nitrogen concentrations between forest and cropland is gradually reduced.In addition,the increasing range of organic and nitrogen deprived from forest in 0-10 cm was higher than 10-20 cm soil depth.?3?The?¹³C and?¹⁵N natural abundance in aggregates were in the order of macroaggregates<microaggregates<silt+clay size class,and there was little difference between macroaggregates and microaggregates.The newly imported organic carbon and total nitrogen were mainly concentrated in large aggregates and microaggregates.?4?Re-vegetation can increase the cumulative mineralization of soil organic carbon and total nitrogen,and the effect differed with re-vegetation age.Soil carbon and total nitrogen in 0-10 cm were both 1.43 time that of 10-20 cm soil depth.There was positive correlation between the cumulative mineralization of soil organic carbon and total nitrogen and the contents of organic carbon and total nitrogen deprived from forest.The result showed that the new input organic carbon and nitrogen can promote the mineralization of soil carbon and nitrogen,and they all affected by aggregates,C/N ratio and soil depth.