Effects And Mechanism Of Soil Carbon And Nitrogen Sequestration Following Desertification Reversion In MU US Sand Land

Desertification is one of the most serious types of land degradation phenomenon in the world at present,a lot of vegetation reconstruction and ecological restoration project had been launching in everywhere,it has an important theoritical and practical significance for understanding,practice and evaluation of desert area to explore the effect of the reversal process and mechanism.As the component of soil fertility,organic carbon and nitrogen can indicate the effect and mechanism to the restoration and desertification land management.Consequently,based on long-term field tracking survey,this article selects the typical desertification in Yulin Hongshixia sandy lands-semifixed lands-fixed lands which recovery year of 20a,30a,51a of shrubs and trees as the research object.In the process of reverse recovery of desertification,analysis of soil composition were carried out indoor,we have a research of the changes of soil total organic carbon,nitrogen,sand,silt,clay with combined organic carbon,total nitrogen,light fraction and heavy fraction with carbon nitrogen,active oxide organic carbon with the extension of projects in the recovery evolution of the characteristics,retaining ratio as well as different carbon and nitrogen components decomposition resistance stability,reveals the effect and mechanism of soil carbon and nitrogen fixed sandy in the the process of desertification reversion in study area.The main results were getted following:（1）soil total organic carbon content in 0⁵cm of 51a shrub and 51a tree are respectively 10.7 and 11.3 times than flow sand,9.0 and 9.2 times in nitrogen.At the same time,soil total organic carbon content of different recovery year in 0⁵cm is 1.9³.4 times than in 5¹0cm and 10²0cm soil layer,1.8⁴.0 times in tree;soil total nitrogen content of different recovery year in 0¹0cm is 2.2⁴.7 times than in 10²0cm soil layer,2.5³.9times in tree.According to the soil particle size grouping,sand carbon,silt carbon in 0⁵cm soil layer of 51a shrub and 51a tree are 2.5 and 2.7 times,1.8 and 2.6 times than clay carbon;sand nitrogen,silt nitrogen in 0¹0cm soil layer of 51a shrub and 51a tree are 1.3and 1.1 times,1.9 and 1.6 times than clay nitrogen.The density growth of sand,silt and clay carbon in 0⁵cm soil layer of shrub soil were 0.05,0.05 and 0.02 Mg/hm²·a;the density growth of sand,silt and clay carbon in 0⁵cm soil layer of shrub soil were 4.4,4.0and 2.5 Mg/hm²·a.According to the light and heavy fraction,the organic carbon content of light fraction of 51a shrubs and 51a trees was 1.3 and 4.9 times respectively than heavy fraction;the nitrogen content of light fraction of 51a shrubs and 51a trees was 0.5 and 1.6times respectively than heavy fraction.According to the active organic carbon and inert organic carbon group,the oxidative active organic carbon content of 20a shrub and 51a shrub was 2.0 and 1.2 times than that of 20a trees and 51a trees.（2）The contribution rate of the respective particles carbon to the total organic carbon in 0²0cm soil layer of the 51a shrub was,silt carbon 42.6%>sand carbon 33.2%>clay carbon 24.2%;the contribution rate of the respective particles carbon to the total organic carbon in 0²0cm soil layer of the 51a tree was,silt carbon 36.0%≈sand carbon36.0%>clay carbon 27.1%,it can be seen that the carbon and nitrogen in silt and sand contributed more to the soil caobon.The proportion of the light fraction carbon to total organic carbon of 51a shrubs and 51a trees increased from 35.4%in the semifixed land to57.4%and 83.1%,while the proportion of the light fraction nitrogen to total nitrogen of51a shrubs and 51a trees increased from 6.6%in the semifixed land to 31.4%and 61.3%.The active organic carbon oxide percentage of total organic carbon in two kinds of forest land in restoration process achieve to peak in 20a,and the active organic carbon oxide percentage of 20a shrubs and 20a trees soil increased from 17.4%in the semifixed land to41.3%and 27.2%respectively.It can be seen that the proportion of active carbon and light fraction carbon and nitrogen is increased gradually,which plays an important role in sequestration of carbon and nitrogen.（3）The abundance ofδ¹³C in the whole soil is similar to that of the litter layer,and there is no significant difference of woodland in the recovery process during the reversion of desertification.The abundance ofδ¹³C of each particles carbon in shrub was always reduced in the quicksand-20a shrub process,and increased in the 20a-51a shrub process.The abundance ofδ¹⁵N in the silt nitrogen and clay nitrogen is similar to that of the litter layer,the abundance ofδ¹³C of sand carbon and total soil in shrubs/trees was always increased in the quicksand-20a shrubs/trees process,and reduced in the 20a-51a shrubs/trees process.（4）The relaton of cumulative CO₂ emission content of different recovery year of shrub soil is semifixed sandy land<51a shrub<30a shrub<20a shrub,while the relaton of cumulative CO₂ emission content of different recovery year of tree soil is semifixed sandy land<51a tree<20a tree<30a tree.After 60 days of culture,the organic carbon content of light fraction of 51a shrubs and 51a trees decreased by 58.6%and 88.72%compared with that before culture,and the organic carbon content of heavy fraction reduced by 5.0%and 3.0%only;while,the nitrogen content of light fraction decreased by60.8%and 85.6%compared with that before cultivation,and the nitrogen content of heavy fraction reduced by 13.7%and 2.9%only.The proportion of organic carbon decomposition of light fraction after cultivated in semifixed land,51a shrubs and 51a trees was 79.2%,91.6%and 97.8%,the proportion of nitrogen decomposition of light fraction after cultivated in semifixed land,51a shrubs and 51a trees was 3.2%,53.1%and 98.7%.Semi-fixed sand after the training,51a shrub group and 51a tree light soil organic carbon decomposition measure of total organic carbon decomposition ratio of 79.2%,91.6%and97.8%,after the training of semi-fixed sandy shrub,51a group and 51a tree light soil nitrogen amount amount of total nitrogen ratio of 3.2%,53.1%and 98.7%.It can be seen that the soil light fraction activated carbon nitrogen is the main carbon and nitrogen decomposition loss in the restoration of fixing sand forest.In conclusion,it brings significant effects of soil carbon and nitrogen sequestration in the reverse process of desertification in MU US sandy land,and the effect of carbon and nitrogen sequestration in forest was stronger than that in shrub.The carbon and nitrogen combined with sand and silt is mainly mechanism of sequestration in the storage of soil components.The storage content of carbon and nitrogen in the light fraction is higher,the activity is stronger and the stability is weaker,provide a quick turnover of carbon and nitrogen for the soil vegetation environment;while carbon and nitrogen of heavy fraction is not easy to decompose,which has great influence to the stability of carbon and nitrogen and to prevent soil nutrient loss.