Search

Biological soil crusts occur in dry land worldwide. However, studies on the carbon exchange of crusts with different histories of crust development are rare, especially in terms of the responses of carbon exchange to increasing atmospheric CO2 concentrations and decreasing water contents of crust organisms. In this study, we classified sites in Shapotou in the Tengger Desert as recent (site revegetated in 1981 in mobile sand dunes) and old (site revegetated in 1956) successional stages, and systematically analyzed the changes in the carbon exchange of cyanobacterial-algal crusts developed in the two sites to dehydration, air temperature (15 and 25 °C), and CO2 concentration (200–2000 ppm). The old crusts had a higher carbon exchange rate than the recent crusts during dehydration, and the maximum carbon exchange rates were 3.49 and 2.45 µmol · m−2 · s−1 for the old and recent crusts, respectively, at an approximately 60% water content of dry crust organisms. The carbon exchange rate was higher at 25°C than at 15°C for both crusts. No difference in the CO2 saturation points between the two crusts and between the two temperatures was observed, however, the saturation point significantly increased with the increase in the water content of the crust organisms, from 224 to 1384 ppm, when the water content of the crust organisms was increased from 20% to 100%. The water content of the crust organisms was the regulating factor for the carbon exchange rate of both the old and recent cyanobacterial-algal crusts. [ABSTRACT FROM AUTHOR]

Quantification of the relationship between surface albedo and surface temperature was done by analyzing measured diurnal variations of surface albedo and surface temperature on the biological soil crusts and sand dunes within vegetation-stabilized desert ecosystems. The surface albedos and surface temperatures of sand dunes and biological soil crusts were measured concurrently over field plots of the moving sand area and the artificially revegetated area established in 1964 in Shapotou area, on the southeastern edge of the Tengger Desert. Results indicated that the diurnal variation of surface albedo for both dry surfaces showed an upward-facing parabolic curve on clear days and was symmetrical at about local noon. Whereas, the diurnal trend of surface temperature was opposite to that of surface albedo in the daytime and asymmetrical at about local noon times. Thereby, the data were empirically divided into forenoon and afternoon data with respect to local noon to analyze the relationship between surface albedo and surface temperature. A highly correlated negative linear relationship was found in the two time periods, respectively, and we proposed an empirical model between surface albedo and surface temperature based on that relationship. The model results indicate a good potential application for using the surface temperature to specify surface albedo. [ABSTRACT FROM AUTHOR]