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Monitoring soil CO2 respiration with chamber measurements and identifying controlling factors such as the diversity of vegetation species, moisture and temperature can help guide desert scrubland management. Soil CO2 respiration and potential controlling factors at four sites in desert scrubland were examined along the Sangong River Basin (SRB) in northwestern China in 2004. Soil CO2 respiration descended along the SRB as did the diversity of vegetation species, air temperature and air humidity. The two sites of the field station (FS) and the north desert (ND) and the low reaches of the SRB among these locations were monitored to analyze the effects of pH value, soil organic carbon (SOC), total nitrogen (TN) and calcium carbonate (CaCO3) on soil CO2 respiration during the growing season in 2005. The ND site was located at the southern edge of the Gurbantunggut Desert; the FS site was in the border area of the SRB Alluvial Fan. One-way ANOVA was performed. The result showed that air humidity and CaCO3 content had a strong influence on soil CO2 respiration; SOC content was a limitation to soil CO2 respiration in the arid-desert zone. Effective management activities can attenuate soil CO2 respiration and keep carbon balance trends at a desirabe level in desert scrublands. [ABSTRACT FROM AUTHOR]

Various extraction methods have been used to determine selenium (Se) concentrations in soils and plants in the second seleniferous regions of China. Our results show tea Se contents in the study area range from 1.009 to 2.6 mg/kg, which reveal that the tea areas in Ziyang County are in seleniferous regions. The four extraction methods evaluated in this study provide different information concerning soil and plant Se levels. The quality control/quality assurance program for this project indicated there is excellent agreement between total soil Se and extractable Se. For example, phosphate extractable Se results from the field investigation and greenhouse study were found to be highly correlated ( R 2 > 0.91) by linear regression analyses. Results from rye seedling experiments further show phosphate extractable Se has significant correlations with plant Se uptake and that a 0.1 M solution of KH2PO4 can be used as the extractant of soil available Se. In the acid soil, the Brassica campestris yield could be significantly reduced when the content of Se6+–Se ≥ 0.5 mg/kg, and the influence on the yield was not as obvious when the content of Se6+–Se reached up to 2.0 mg/kg. The uptake by Brassica campestris of Se6+–Se is higher than that of Se4+–Se. The main factors influencing the biological availability of soil Se, in order of their importance are CaCO3, the presence of silt grains, organic matter and the presence of clay grains. pH could affect KH2PO4 extractable Se through CaCO3. [ABSTRACT FROM AUTHOR]