Migration And Transformation Characteristics Of Photosynthetic Carbon And Residual Carbon Of Moss Crust In Mu Us Sand Land

In arid and semi-arid areas,due to limited soil moisture and extreme climate stress,vascular plant coverage is low.Biological crusts are the key active ground covers,and the input of photosynthetic carbon and residual carbon becomes an important carbon source for desert ecosystems.Mosses crust is an advanced stage of biological crust succession.It is of great significance to study the dynamic process of photosynthetic carbon transformation in mosses crust,analyze and quantify the contribution of carbon input from mosses crusts to soil organic carbon pool,and elucidate the action mechanism of microorganisms in the process of carbon transformation in mosses crusts for accurate assessment of desert ecosystem carbon balance.In this study,moss crust in Mu Us Sandy land was taken as the research object,¹³C in situ labelling technology was used to determine the dynamic changes of¹³C in different components of moss crust,and to analyze the migration and transformation process of photosynthetic carbon in moss crust mediated by microorganisms.Laboratory decomposition tests of mosses were carried out to investigate the contribution of mosses crusts to soil organic carbon by measuring the content changes of soil organic carbon and active carbon components.At the same time,the changes of soil enzyme activities and microbial communities after the input of moss crusts were observed and analyzed,and the response mechanism of soil microbial communities and enzyme activities to the decomposition of moss crusts was discussed.The main research results are as follows:1.The concentration of photosynthetic carbon in moss crust was as follows:moss crust plant>moss crust soil>0～1 cm soil layer,and the maximumδ¹³C values reached 181.29‰,23.41‰and-22.28‰,respectively.The photosynthetic carbon of moss crusts remained for a long time in both aboveground plant and crusted soil,and there was still some residue 70 days after labeling,but there was no significant difference inδ¹³C value in the 0～1cm soil layer compared with before labeling.2.The absolute content of ¹³C in soil organic carbon pool,soil microbial biomass carbon pool and soil soluble organic carbon pool varied from 3.4 to 10.78mg·kg^-1,0.01 to 25.18μg·kg^-1and 1.48 to 222.748μg·kg^-1,respectively,with the migration and transformation of photosynthetic carbon.The changes of ¹³C absolute content of soil microbial biomass carbon enrichment(¹³C-MBC)and ¹³C absolute content of soil soluble organic carbon enrichment(¹³C-DOC)mainly occurred within35 days after labeling and changed rapidly.The ¹³C absolute content of soil organic days after labeling.In other sampling periods,there were small fluctuations and no significant differences.The order of photosynthetic carbon retention time of different organic carbon pools was soil organic carbon pool>soil soluble organic carbon pool>soil microbial biomass organic carbon pool.3.The efficiency of ¹³C uptake by different microorganisms in moss crust was significantly different,and the minimum and maximum values ofδ¹³C were-19.12‰and 191.12‰,respectively.The main markers of photosynthetic carbon enrichment were different at the end of the labeling experiment,10 days after labeling,35 days after labeling and 70 days after labeling,which were 16:0,i15:0,18:2w6c and a15:0,respectively,and theδ¹³C value decreased gradually with the migration and transformation of photosynthetic carbon.During the 70-day observation period,fungi and Gram-positive bacteria were the main microbial communities that enriched photosynthetic carbon in moss crust.With the growth and development of moss crust,the distribution difference of ¹³C in different markers of soil microorganisms decreased gradually.4.Decomposition of moss crusts significantly increased the contents of soil organic carbon（SOC）,soil microbial biomass carbon（MBC）and soil soluble organic carbon（DOC）.Compared with the bare sand control group,SOC,MBC and DOC of moss crusts increased by 74.16%,14.12%and 41.38%in the 112-day decomposition test,and increased by 1.99,0.60 and 0.51 times compared with the initial decomposition stage,respectively.The addition of moss crusts significantly reduced the proportion of MBC and DOC in soil organic carbon pool,and promoted the transformation of MBC and DOC.5.The decomposition of moss crusts significantly increased the PLFAs contents of various soil microbial groups and affected the composition of microbial community.The ratio of fungi and bacteria increased during the 56 days of decomposition and decreased from the 56 days to the 112 days of decomposition.The ratio of Gram-positive bacteria to Gram-negative bacteria（G+/G-）showed a"W"-shaped trend during decomposition.After 112 days of decomposition,the activities of peroxidase and cellulase were significantly increased,while the activity ofβ-1,4-glucosidase was significantly decreased.Cellulase activity was the main factor that significantly affected the content of PLFAs in microbial communities.