[Responses of soil potential carbon/nitrogen mineralization and microbial activities to extreme droughts in a meadow steppe]. / 草甸草原土壤碳/氮矿化潜力及土壤微生物水分敏感性对极端干旱的响应.

The mineralization of soil carbon (C) and nitrogen (N) is a critical process in the cycling of C and N in terrestrial ecosystems, which is strongly controlled by water availability. In this study, we collected soil samples in a 3-year extreme drought experiment in a meadow steppe in Inner Mongolia, freeze-dried these samples, and measured the potential C and N mineralization rates and water sensitivity of soil microorganism by incubating soils under soil water contents (SWC) of 3%, 8%, 13%, 18%, 25% and 35%. The results showed that averaged across different SWC, the extreme drought treatment of reducing 66% precipitation in growing season significantly increased potential N mineralization rate by 14.2%, but did not affect the potential C mineralization. Extreme drought significantly increased soil microbial biomass N and soil dissolved organic C by 26.8% and 26.9%, respectively. In both the control (natural rainfall) and extreme drought treatment, the potential C and N mineralization and microbial biomass C and N increased with SWC in the incubation, which was possibly caused by the enhanced substrate diffusion. Extreme drought also promoted the initial pulse response of C mineralization, implying the enhanced microbial response to water availability. Extreme drought significantly reduced the ratio of the potential soil C mineralization to the potential N mineralization, suggesting that extreme drought might weak the coupling of soil C and N. Extreme drought could cause different responses to soil water availability between soil C and N cycling. Extreme drought could enhance microbial response to increasing water availability, weak coupling between soil C and N, with consequences on nutrient cycling and primary productivity in the meadow steppe of northern China.

Population pharmacokinetics of propofol in Chinese patients.

AIM: To analyze population pharmacokinetics of propofol in Chinese surgical patients using a nonlinear mixed-effect model (NONMEM) program and to quantitate the effects of covariance of gender, age, and body weight. METHODS: The population pharmacokinetics of propofol was investigated in 76 selective surgical patients (37 males and 39 females aged 19-77 a, weighing 39-86 kg). A total of 1439 blood samples were analyzed using NONMEM (NONMEM Project Group, University of California, San Francisco, CA). Interindividual variability was estimated for clearances and distribution volumes. The effects of age, body weight, and gender were investigated. RESULTS: The pharmacokinetics of propofol in Chinese patients was best described by a three-compartment pharmacokinetic model. Body weight was found to be a significant factor for the elimination clearance, the two inter-compartmental clearances, and the volume of the central compartment. The volumes of the shallow peripheral compartment and deep peripheral compartment remain constant for all individuals. The estimates of these parameters for a 60-kg adult were 1.56 L/min, 0.737 L/min, 0.360 L/min, 12.1 L, 43 L, and 213 L, respectively. For old patients, the elimination clearance and volume of the central compartment decreased. CONCLUSION: The pharmacokinetics of propofol in Chinese patients can be well described by a standard three-compartment pharmacokinetic model. Inclusion of age and body weight as covariances significantly improved the model. Adjusting pharmacokinetics to the individual patients should improve the precision of target-controlled infusion system.