ABSTRACT
The role vegetation restoration and succession play in regulating Nitrogen (N) and Phosphorous (P) pools remains unexplored and poorly understood. To examine the effects of vegetation restoration and succession from a shifting sand dune to restored vegetation at different ages (23, 33, 50, and 58 years) on the dynamics and distribution of N and P pools in a soil-plant system, a comprehensive field investigation was conducted and N(P) concentrations and densities of soil, shrubs (including leaves, new branches, aging branches, and roots), and grass (including aboveground, roots, and litter) at each site were analyzed and quantified. We found that total N (TN) and total P (TP) density for the plant-soil system, in live shrub biomass as well as soil TN (STN) density in subsoil (10-100â¯cm), decreased between 23 and 50 years, and then increased from 50 to 58 years. STN and soil TP (STP) densities in topsoil (0-10â¯cm), and N and P densities of herbage and dead shrubs, continued to increase with restoration. N and P were primarily stored in soils and accounted for 89.83%-92.06% and 99.33%-99.48% of the TN and TP pools, respectively. In the first 23 years, live shrubs made up the second largest N and P pools, however, herbage made up the second largest N and P pools after 23 years. The ratios of N and P in herbage to TN and TP density increased from 3.71% to 6.31%, and 0.33%-0.43%, gradually approaching the native site (6.39% and 0.46%). The ratios of N and P in live shrubs to TN and TP density in the soil-plant system decreased from 4.55% to 1.08% and from 0.33% to 0.13%. Our results indicated that the restored ecosystem was a N(P) source from 0 to 50 (0-23) years, and a N(P) sink from 50 to 58 (23-58) years, with strong potential for accumulating more N (147.18â¯gâ¯m-2) and P (102.67â¯gâ¯m-2) to reach the natural site levels. These results suggest that vegetation restoration and succession may profoundly alter N and P geochemical cycles through N(P) redistribution in a temperate desert plant-soil system. Proper N and P addition at the initial stage of vegetation restoration may promote the recovery of desertified land.
Subject(s)
Nitrogen , Soil , Carbon , China , Ecosystem , PhosphorusABSTRACT
OBJECTIVE： To establish a method for determination of fluconazole concentration in human plasma. METHODS： UPLC-MS/MS method was adopted to determine plasma after precipitated with acetonitrile. Using isotope fluconazole-d4 as internal standard， the determination was performed on ACQUITY UPLC BEH C18 column with mobile phase consisted of 0.1％ formic acid-acetonitrile （gradient elution） at the flow rate of 0.3 mL/min. The column temperature was 40 ℃， and the sample size was 3 μL. ESI was used for positive ion scanning by multiple reaction monitoring mode. The ion pairs for quantitative analysis were m/z 307.1→220.0 （fluconazole） and m/z 311.1→223.0 （internal standard）. RESULTS： The linear range of fluconazole was 10-5 000 ng/mL （r＝0.998 1）. The limits of quantitation was 10 ng/mL. RSDs of intra-day and inter-day were less than 8％； accuracy ranged 95.8％-106.7％. The extraction recovery ranged 97.3％-107.3％ （RSD＜5.0％， n＝6）， and matrix effect， dilution effect and residual effect didn’t influence quantitative analysis of the substance to be measured. CONCLUSIONS： The method is simple， rapid， specific and accurate， which can be used for therapeutic drug monitoring and pharmacokinetic study of fluconazole.
ABSTRACT
Objective: To establish a GC determination method for the content and dissolution of magnesium valproate tablets. Methods:Magnesium valproate tablets were detected by a GC internal standard method. The samples were dissolved in 0. 1 mol·L-1 hydrochloric acid solution, and then extracted by dichloromethane. Eicosane was used as the internal standard. The dissolution was de-termined by the first method described in ChP 2015 edition. The dissolution medium was 0. 1 mol·L-1 hydrochloric acid solution and the rotation speed was 100 r·min-1 with the sampling time at 45 min. The samples were extracted by dichiormethane, and eicosane was used as the internal standard as well. Results: The dissolution of magnesium valproate tablets showed good linearity within the range of 0. 005-1. 000 mg·ml-1(r=0. 9999). The recovery was 99. 2% (RSD=0. 5%, n=9). The dissolution curve showed that magnesium valproate released above 80% in 45 minutes. Conclusion:The method has good specificity and high accuracy, and can be used for the content determination and dissolution detection of magnesium valproate tablets.
ABSTRACT
OBJECTIVE:To establish a method for the determination of related substances in Lovastatin tablet. METHODS:HPLC was performed on the column of Waters XTerra? MS C18 with mobile phase A of 0.01%Phosphoric acid solution and B of acetonitrile(gradient elution)at a flow rate 1.0 ml/min,column temperature was 40 ℃,the detection wavelength was 238 nm,and the injection volume was 10 μl. RESULTS:The impurity components were well separated in principal components;the linear range of lovastatin was 17.5-700 μg/ml(r=0.9999);RSDs of precision,stability and reproducibility tests were lower than 1%;recov-ery was 99.30%-100.67%(RSD=0.4%,n=9). CONCLUSIONS:The method is reproducible with good durability and high preci-sion,and can be used for the quality control of Lovastatin tablet.
