| Biological crust is the main contributor to the organic carbon of the desert ecosystem in arid areas.In order to study the characteristics of organic carbon and the process of carbon fixation of biological crusts at a regional scale,this study took two types of typical biological crusts(moss crusts and cyanobacteria crusts)in the Mu Us sandy land as the research objects.Set up 45 typical sample plots to measure the organic carbon(SOC)content,organic carbon density(SD)and organic carbon components(soluble organic carbon DOC,microbial biomass carbon MBC,easy oxidized organic carbon(ROC),particulate organic carbon(POC)content,using multivariate mathematical statistics methods to analyze the relationship between climate,soil,vegetation and the characteristics of biological crust organic carbon,and discuss the main controlling factors of organic carbon characteristics on the regional scale.At the same time,the photosynthesis and respiration characteristics of biological crusts in the dry and rainy seasons were observed and analyzed at the plot scale,and the decomposition process of bryophyte litter was taken as an example to analyze the biological formation under different environmental conditions.The main results are as follows:(1)Biological crusts have a significant(p<0.05)improvement effect on the SOC content,SD,and organic carbon content in the study area.On a regional scale,the SOC and SD of the biological crust observation layer(biological crust layer and 0-10cm soil layer on the surface)are significantly higher in the eastern part of the study area than in the western part;The SOC content of the two types of biological crusts and the underlying soil decreases with the increase of soil depth;The order of SD size of observation layer of different types of biological crusts is moss crust(0.37kg/m~2)>cyanobacteria crust(0.22 kg/m~2)>bare sand control(0.18 kg/m~2);Compared with moss crusts,cyanobacteria crusts have a higher risk of organic carbon loss;The organic carbon of the soil layer under biological crusts is more stable than that of the crust.(2)This study shows that among the influencing factors discussed,the SOC and SD of biological crusts are mainly affected by climatic factors,and the content of organic carbon components is mainly affected by soil factors.On the regional scale,the main influencing factors of SOC and SD of moss crust are slope aspect,cation exchange capacity,and potential evapotranspiration.The main influencing factors of SOC and SD of cyanobacteria crust are wind speed,aspect and water vapor partial pressure;The organic carbon content of the two types of biological crusts are closely related to temperature,light,soil mechanical composition,pH,and electrical conductivity;The physical properties of the soil have a significant impact on the proportion of active organic carbon in the biological crust in the study area.(3)Two types of biological crusts show net carbon release in the dry season and net carbon absorption in the rainy season.The photosynthetic rate and soil respiration rate in the rainy season are significantly higher than those in the dry season.Moss crust photosynthesis,respiration rate,and cyanobacteria crust photosynthetic rate decreased from morning to night in a single day in the dry season.Cyanobacteria crust respiration rate showed a change characteristic of first increasing and then decreasing around 10:00;The diurnal changes of photosynthetic rate of moss crust and algae crust in the rainy season showed the characteristics of a bimodal curve,and the diurnal change of respiration rate showed the characteristics of a single-peak curve that first increased and then decreased.The main limiting factor of photosynthesis and respiration rate is the air humidity near the ground.(5)The decomposition process of bryophyte litter in the study area is mainly concentrated in the rainy season.After the 7-month test period,the residual rate of moss litter in the three plots from southeast to northwest showed that the southeast plot(Yulin,92.54%)<the central plot(Wushen Banner,93.53%)<the northwest plot(Etuoke Banner,95.34%),indicating that the decomposition rate of bryophyte litter is the same as the change trend of the average annual precipitation of the sample plot. |
PDF Full Text Request