中文摘要：

采集珠江三角洲平原20个农田不同发生层的土壤样品,研究了土壤有机碳（SOC）及其组分,包括高锰酸钾氧化碳（POXC）、不同浓度硫酸氧化的有机碳组分（CF1、CF2、CF3和CF4）、胡敏酸碳（HAC）、富里酸碳（FAC）和胡敏素碳（HMC）的分布特征及其相互关系和影响因素。结果表明：SOC含量变幅为1.88-52.78 g kg^-1。SOC、CF1、CF2、CF3、POXC、FAC、HAC含量均在耕作层（Ap1）中最高,平均值分别为17.87、7.29、4.32、2.57、0.58、1.72、2.60 g kg^-1,在水耕氧化还原层（Br）中最低;CF4和HMC含量在Bg层土壤中最高,平均值分别为5.32、15.03 g kg^-1。Ap1、Ap2、Br、Bg层中POXC占有机碳比例平均值分别为3.2%、3.3%、3.5%、3.6%,活性有机碳（CF1＋CF2）是土壤有机碳的主要组分,在各发生层土壤中所占比例均〉60%。土壤腐殖质以HMC为主,所占比例约80%。土壤有机碳及其各组分之间均呈极显著正相关,土壤有机碳及其组分与土壤全氮、碱解氮呈极显著正相关,与pH值呈显著负相关。

英文摘要：

Soil samples were collected from twenty agricultural soils based on genetic horizon in the Pearl River Delta plain. Soil organic carbon （SOC） fractions including permanganate oxidizable carbon （POXC）, different concentrations of H2SO4 oxidizable carbon （Cry, Cr2, Cr3 and Cr4）, humic acid C （HAC）, fulvic acid C （FAC）, humin C （HMC） were determined. This paper studied the characteristics of SOC fraction and analyzed the relationships between SOC and relative fractions as well as their affecting factors. The results indicated that SOC contents varied from 1.88 to 52.78 g kg^-1. The contents of SOC, CF1, Cr2, Cr3, POXC, FAC and HAC were the highest in plough layer, with the averages of 17.87, 7.29, 4.32, 2.57, 0.58, 1.72, 2.60 g kg-1, respectively, but was the lowest in Br horizon; The contents of C~4 and HMC were the highest in Bg horizon, and the mean concentrations were 5.32 and 15.03 g kg^-1, respectively. The percentages of POXC in Apl, Ap2, Br and Bg horizon were 3.2%, 3.3%, 3.5% and 3.6%, respectively. The labile organic C （CF1 ＋ Cn） was the dominate fraction of SOC, and the percentage of labile organic C in all soil horizons were larger than 60%. HMC was the dominate fraction of humus, which accounted for about 80%. There existed significantly positive correlation between SOC and its fractions. SOC and its fractions had significantly positive correlation with soil total N, available N, and significantly negative correlation with soil pH.