The Study Of Characteristics Of Photosynthetic And Soil CO₂ Flux Of Biocrusts In MU US Sandland

In recent years,under the background of global climate change,the exchange of carbon dioxide between arid and semi-arid ecosystems and atmosphere has become a hot issue.MU US desert is an important part of arid and semi-arid system,which windly distributed by biocrusts and the highst coverage is up to 70%.Biocrusts can increase soil organic carbon through photosynthesis,which make effects on soil respiration and plays an important role in maintaining regional carbon balance.However,many studies related to the soil carbon cycle of desert ecosystem have neglected the effects of biocrusts.Biocrusts widely spreading in the MU US sandland.We choosed moss and algae crusts as our research subjects in the study.An investigation of the distribution and growth of biocrusts,the characteristics of photosynthetic and soil respiration of biocrusts were studied,and influence factors were analyzed.The objective of the study is to provide support for an estimation of the photosynthetic carbon sequestration and to provide references for the study of carbon balance in desert regions.The main conclusions are as follows:?1?Relative to the soil layer,the organic matter,total nitrogen and total phosphorus content of biocrusts were significantly increased;the soil pH value was decreased.Compared with dry season?May?,soil organic matter and total phosphorus content increase significantly due to the increase of photosynthetic carbon sequestration and humus mineralization rate in rainy season?september?.The total nitrogen in the soil was partly used to satisfy the metabolic consumption of biocrusts,and some was leached by water to the deep soil,which resulted in a significant decrease in the content of nitrogen in the soil.?2?There were significant differences in photosynthetic rate?p<0.01?of different types of biocrusts,and the photosynthetic rate of the moss crusts was twice that of algal crusts.The diurnal variation of the photosynthetic rate of biocrusts was marked by a double peak curve,which peaks appeared at around 9:00 and 17:00;and the seasonal variation of the photosynthetic rate of biocrusts was marked by a single-peaked curve.The changing trend of soil temperature and moisture content was basically marked by a single-peaked curve.The photosynthetic rate was significantly positive correlated with soil moisture?2cm,5cm?and air humidity,and negative correlation with soil temperature and near-surface temperature.?3?The biocrusts can significantly decrease soil CO₂ flux,and the soil CO₂ flux under moss crusts and algal crusts decreased by 8.1%and 4.9%before and after removal of biocrusts,respectively.Soil CO₂ flux of biocrusts was decreased by 171%on average under the effect of wet conditions.The diurnal variation of the soil CO₂ flux of biocrusts showed the tread of“double peak”,and the peak appeared at 11:00 and 16:00;the seasonal variation is obvious,with a single-peaked curve and the maximum appearing of soil CO₂ flux of moss and algae crusts in July and August,respectively.?4?Both Q₁₀ of soil CO₂ flux of moss crusts and algal crusts were significantly higher than that of bare ground,1.58,1.65 and 1.51,respectively.There is a significant exponential function relationship between soil CO₂ flux and soil temperature,a significant positive linear function relationship between soil CO₂ flux and soil moisture in 5cm and 10cm?P<0.01?.The correlation of soil CO₂ flux and soil temperature,soil moisture was higher in 5cm,soil CO₂ flux under bare land more sensitive to the change of soil temperature than under biocrusts.