Effects Of Alpine Degradation And Restoration On Soil Aggregate And Organic Carbon In Northwestern Sichuan

The alpine grassland in northwestern Sichuan is located in the common water conservation area in the upper reaches of the Yangtze River and the Yellow River.Grassland degradation and land desertification have been posing a serious threat to the ecological security in the region.Selecting the typical areas of Zoige County and Hongyuan County in alpine grassland in northwestern Sichuan,using the typical indicators to characterize the changes of soil aggregates.The paper initially revealed the characteristics of changes insoilaggregatesandorganiccarbonindifferentstagesof degradation/recovery in the alpine grasslands,and demonstrated effects of adding exogenous carbon on soil aggregates and organic carbon in sandy soil.The main results and conclusions of this study were as follows:（1）Effects of grassland degradation on soil aggregates and organic carbonThere were some significant differences in soil aggregates at different degradation stages of grassland:soil mechanical-stable aggregates and water-stable aggregates of non-degraded grassland were mainly composed of macro-aggregates（>0.25 mm）,while degraded grasslands was mainly composed of micro-aggregates（<0.25 mm）.At the same time,for the R_0.25,MWD and GMD indicators,non-degraded grassland>lightly degraded grassland>moderately degraded grassland>heavily degraded grassland,while,PAD was opposite.Especially,the stability of aggregates was the most obvious in the stage of non-degraded to lightly degraded.The highest value of aggregates organic carbon content appeared in the 0.5² mm size,and macro-aggregates organic carbon content was obviously higher than the micro-aggregates organic carbon.The results showed that the soil organic carbon content and aggregates stability were reduced significantly with the degradation of alpine grassland.（2）Effects of vegetation restoration on soil aggregates and organic carbonVegetation restoration was beneficial to improve aggregates stability and organic carbon content of sandy soil.The recovery level was close to lightly degraded grassland.With the increasing of recovery period,upper 2 mm and0.5² mm mechanical-stable aggregates and water-stable aggregates increased significantly in the surface layer（0²0 cm）,however,which were mainly composed of micro-aggregates（<0.25 mm）.R_0.25,MWD and GMD indicators showed:0 a<5 a<10 a<15 a,PAD presented opposite trend.At the same time,organic carbon content of upper 2 mm and 0.5² mm aggregates increased significantly,and the contribution rates of upper 0.5 mm aggregates to soil organic carbon was 34%⁶0%.（3）Effects of adding exogenous carbon on soil aggregates and organic carbon in sandy soilAfter 150 days cultivation of adding exogenous carbon（wheat straw,corn straw,yak dung,organic fertilizer）under indoor test conditions,the content of upper 2 mm and 0.5² mm particle aggregates were increasing,and yak dung had the strongest improvement on sandy soil aggregates.Simultaneously,with the increasing cultivation time,the content of upper 2 mm aggregates organic carbon was increasing,while,There was no obvious change in organic carbon content in other granular aggregates.The results showed that the adding exogenous carbon was beneficial to improve the structure of desertification aggregates and soil organic carbon.