低山丘陵坡耕地秸秆覆盖轮耕土壤WSOC的荧光特征

为了提高坡耕地的秸秆还田效率，增加土壤有机质，探索一种适于坡耕地的基于种养结合的保护性耕作方式。采用田间小区试验，研究了秸秆覆盖轮耕技术（包括当季秸秆覆盖+休闲、上季秸秆覆盖+旋耕）与常规耕作（秸秆移除后旋耕）对土壤水溶性有机碳（WSOC）荧光特征及团聚体有机碳的影响。结果表明：砂质暗棕壤坡耕地秸秆覆盖旋耕（SRT）、秸秆覆盖休闲（SFT）与秸秆不还田的常规耕作（CRT）处理土壤WSOC均解析出C1，C2，C3和C4等4组荧光组分，主要为紫外光区与可见光区类富里酸（Peak A 和Peak C）、类胡敏酸（F）和短波类色氨酸（类蛋白B、D峰）等成分。秸秆覆盖旋耕处理提高了类富里酸（Peak A和Peak C）和类蛋白组分C4含量，C1和C2组分较覆盖休闲和常规耕作分别提高112.73%，109.35%和107.77%，66.07%，C4组分较SFT与CRT处理提高28.26%和42.31%，差异显著，而常规耕作处理来自于自生源腐殖质组分的胡敏酸C3含量增加，较覆盖旋耕和覆盖休闲处理分别增加16.76%和49.74%；0～20 cm耕层土壤团聚体有机物主要分布在<0.053 mm的矿物质结合态（MOM）中，平均占比为63.90%，其次为0.25～0.053 mm细颗粒态有机物（oPOM），占比为23.8%，粗颗粒态有机物（>0.25 mm）中含量最低，仅为11.2%；与秸秆不还田比较，坡耕地秸秆覆盖还田增加了植物来源的新鲜有机质的形成，表现为＞0.053 mm的闭蓄态有机碳（oPOC）含量的增加，以覆盖旋耕处理oPOC增加较大，而秸秆不还田的CRT处理增加了MOM占比；覆盖旋耕处理FI和HIX值增大，土壤腐殖质积累趋势增强，为低山丘陵区坡耕地实施秸秆覆盖还田的保护性耕作技术提供了科学依据。     

Simultaneous determination of carbonyl compounds and polycyclic aromatic hydrocarbons in atmospheric particulate matter by liquid chromatography-diode array detection-fluorescence detection

Simultaneous analysis of 24 carbonyl compounds (alkanals, unsaturated, dicarbonylic and aromatic aldehydes and ketones) derivatized with 2,4-dinitrophenylhydrazine and 16 polycyclic aromatic hydrocarbons (PAHs) using a photodiode-array (PDA) and a fluorescence (FL) detector in series is proposed.The separation is carried out with a reversed-phase column and gradient elution using four solvents (acetonitrile, water, tetrahydrofuran and methanol) in less than 35 min. Several critical pairs of carbonyl compounds with 3 and 4 carbon atoms and different functional groups, isomers of tolualdehyde, aromatic and aliphatic aldehydes were conditional on the gradient elution. Common pre-treatment for two groups of compounds consists in a step of extraction and derivatization in aqueous medium and a further clean-up using a polymeric phase SPE and concentration in a mixture of dichloromethane:methanol. A pre-concentration factor of 50 was achieved by this procedure. Acetone and formaldehyde blanks were minimized and remain controlled with a specific cleaning of glass material and washing the SPE cartridge.The limits of detection (LOD) ranged from 0.006 to 0.18 ng mL⁻¹ for PAHs and from 2.4 to 10.1 ng mL⁻¹ for carbonyl compounds and method precision was ≤15% for all analysed compounds. Recoveries were within the range of 95-104% for PAHs except for more volatile compounds (acenaphthene and fluorene) and within the range of 72-113% for carbonyl compounds. The method was applied in water-soluble fraction of PM₁₀ (atmospheric particulate matter with an aerodynamic diameter less than 10 μm) and the spectral contrast technique was used in the identification of carbonyl compounds.