Capacity And Mechanism Of Soil Carbon Sequestration At Typical Sand-fixed Forests In Mu Us Sand Land Of Yulin

Desertification is one of the most serious types of land degradation in China,and it is of great scientific significance to explore the process and mechanism of reversal recovery for cognition and guidance of ecological restoration as well as reconstruction in desertified areas.Because organic carbon is a key indicator of soil fertility and ecological restoration effect evaluation.Therefore,this study selected quicksand land,semi-fixed sand and fixed sand lands that were established by shrubs and arbors for 20⁵1 year-old at MU US sand land of Yu Lin as the research objects.Based on the field investigation and laboratory analysis,the changes of soil surface litter,surface root,soil total organic carbon,soil organic carbon in sand,silt,clay and the key driving factors were studied.The main results were as following:?1?Compared with the quicksand,the total organic carbon content of shrub and arbor sand-fixed forest lands increased significantly with recovery year,and considerably reduced with the increasing soil depth from 0¹0 to 10²0 cm.In the 0²0 cm soil layer,the soil organic carbon content of sand-fixed forest lands in different restoration years was significantly higher than that in quicksand.After 51-year shrub and arbor vegetation,while the soil total organic carbon in 0²0 cm increased by 7.4 times and 8.0 times compared to quicksand area.Sand fixed forest from 20-year-old to 51-year-old,the soil total organic carbon density increased by 2.6⁷.4 times compared to quicksand area,and the litter carbon density and root carbon density increased by 19.0⁷0.5 times and 2.6⁸.6 times,respectively,compared with semi-fixed sandy land.In general,the soil total organic carbon density of the 51-year-old sand fixed forest land was 5.6 times of litter carbon density,which was 10.4 times of the root carbon density.?2?The carbon content of all soil particles sized fractions at the two kinds of sand-fixed forest lands increased linearly with the extension of the vegetation restoration period,and the maximum carbon content was observed in the 0¹0 cm soil layer.From quicksand to sand-fixed forest lands that was stand with 51-year-old shrub and arbor,the annual growth rate of carbon density in silt of 0²0 cm soil depth was 0.11 Mg·hm^-2·a^-1 and 0.12 Mg·hm^-2·a^-1,and the rate of carbon growth in sand was 0.12 and 0.11 Mg·hm^-2·a^-1,while in clay was significantly very low with 0.07 and 0.08 Mg·hm^-2·a^-1 at shrub and arbor vegetation,respectively.In contrast,in the 0²0 cm soil layer,the carbon density growth rate for all the soil particles was average 2.8 times higher than 0¹0 cm soil layer.The average percentage that contributed to accumulation of soil organic carbon by different particles was in the order: silt carbon?39.7%?? sand carbon?34.6%?> clay carbon?26.6%?.?3?The vegetation restoration by establishment of shrub and arbor plantations on Mu Us Sand Land,resulted in significant improvement in soil physical,chemical and biological properties,except pH and total potassium content,especially the 0¹0 cm soil layer was significantly higher than 10²0 cm.In the 0¹0 cm soil layer,the contents of nitrogen,phosphorus and potassium in sand-fixed forest land under different recovery year were increased by 0.9¹1.8 times,0.2¹.0 times and 0.3³.9 times,respectively,compared with the semi-fixed sandy land,while microbial biomass carbon and nitrogen increased by 1.3⁸.1 times than semi-fixed sandy sand,catalase,urease,alkaline phosphatase and invertase activities increased by 1.7⁶.8 times,0.4⁸.5 times,0.6⁸.9 times and 0.6⁹.5 times,respectively,compared with semi-fixed sandy sand.Therefore,the soil biological characteristics of sand-fixed forest were significantly higher than those in soil physical and chemical properties,and the response to vegetation restoration was more sensitive.?4?The principal component analysis showed that the change of soil properties during the vegetation restoration process can be classified as two main components with biological properties and physicochemical properties,and represent the variation of 52.45% and 14.82%,respectively.According to this principal component analysis,the recovery status of different sand-fixed forest was from good to bad: 51-year-old>30-year-old>20-year-old sand-fixed forest> semi-fixed sand.The correlation analysis and redundancy analysis?RDA?showed that there was a significant positive correlation between soil total organic carbon,organic carbon in sand,silt,clay and soil factors,in addition to pH,soil bulk density,C/N ratio and total potassium.In terms of biological factors,the increase of soil carbon pool is most sensitive to the changes of microbial biomass carbon and nitrogen,catalase and urease activities.In terms of soil physical and chemical factors,the increase of carbon pool is most sensitive to the change of total nitrogen and available potassium.In summary,the recovery process of sand-fixed forest in Mu Us sand area of Yulin showed significant carbon sequestration effect,and organic carbon was mainly deposited in combination with soil sand and silt.At the same time,soil physical,chemical and biological properties were closely related to the accumulation of soil total carbon pool and its particle components,especially,the effects of soil microbial biomass carbon and nitrogen,catalase,urease,total nitrogen and available potassium on the soil carbon pool were the most significant,which were the key driving factors of soil carbon pool accumulation in Mu Us sand area.