Photosythetic Carbon Fixation Of Biological Soil Crusts In MU US Desert And Their Impact On Soil Carbon Emission

Biological soil crusts are widely spreading in the world and they are the crucial part in desert ecosystems. They have rich species compositon, complicated structure and they have particular physiological and ecological characteristicsc. The cover of the vascular plants was rather low, and the cover of the biological soil crusts was more than70%of the total cover. Available researched proved that their presence enhanced the organic carbon in the soil, while the value of the carbon fixation varied between two magnitudes by direct measurement, in addition, litter works has been done in the field condition. It is an important complementarity for comprehensively cognizing the ecological function of biological soil crusts whose cover was more than40%percent in the arid environment. This study is an important precondition to recognize the energy flow and matter flow in the desert ecosystem, and it will supply basic data for recognizing the ecological functions of desert ecosystem in the global change, carbon balance in the global.Biological soil crust widely spreading in the Yanchi research station in Mu Us sandland. Algae lichen and moss soil crusts were selected as the research objects in this study. The response of environmental factors to photosynthesis of biological soil crust in laboratory and photosynthetic carbon fixation and carbon release in field was measured using Li-6400-17photosythetic system and Li-8150automated chamber system. The objective of the study is to understand the role of biological soil crust in carbon cycle.The main conclusions are as follows:(1) Water was the main factor influence photosysnthesis of biological soil crust, average optimumwater content and water compentsation point were showed:algae<lichen<moss, The value of water compensation point of photosynthesis was lower than water compensation point of dark respiration which make carbon miss during hydration.The viable temperature range for photosynthesis of biological soil crust is quite wide, Optimum temperature for photosynthesis of cyanobacteria, lichen, and moss was20～27℃,15℃and20℃, respectively. Light saturation point was showed:lichen<algae<moss, and light compensation point was showed:moss<algae<lichen. Study on the response of biological soil crusts on environmental factors can clearly understand the environmental requirements of carbon fixation by photosynthesis, also can explain the distribution characteristics of biological soil crust in the area of space.(2)Biological soil crusts have the characteristics of nutrient enrichment, but the effect on the soil nutrient was restricted to the surface soil. The potential net photosynthetic carbon sequestration were showed:algae<lichen<moss, carbon fixation was51.57、32.71and30.64g C m-2a-1, respectively. Although the requirement of water for photosynthesis of algae was lower than moss, the main factor influenced carbon fixation was net photosysthetic rate.(3)Algae and moss crusted soils were able to reduce C02emissions from soil to atmosphere, while lichen crusts had no significant effect on carbon emissions from soil. Disturbance of BSCs transforms soil from carbon sinks into carbon source under drought conditions. Loss of protective cover of bio-crusts, and fine-grained material decreased leading to nutrient depletion in disturbed sites.This study is meaningful to evaluate BSC carbon fixation and understand carbon cycling process of desert ecosystems, providing theoretical basis to management and arrangement of desertification controls.