土地利用方式对土壤溶解性有机碳组成的影响

选取河北曲周、北京顺义和山东寿光的成对的农田(小麦-玉米轮作)和菜田土壤为研究对象,比较两种土地利用方式下DOC的含量、剖面分布以及组成特征。结果表明:与农田相比,菜田表层有机碳(SOC)与全氮(TN)含量上升。其中菜田有机碳含量较农田增加3.16%~47.4%,全氮含量增加3.09%~64.1%。土壤C/N与pH降低。无论是在农田还是菜田,DOC含量均随着土壤深度增加而显著降低;三地区菜田表层DOC含量平均为农田DOC含量的1.70倍;DOC与SOC成显著正相关关系。两种土地利用方式下,DOC组成中亲水组分(H IM)比例最高,其次为憎水酸性组分(HOA),憎水中性物质(HON)和憎水碱性物质(HOB)的含量最低;菜田中憎水酸性物质比例为19.0%~26.7%,农田憎水酸比例为14.83%~16.42%;寿光地区农田与菜田憎水酸含量差异显著(p<0.05),可能与寿光菜田土壤较高的SOC含量和较低的pH有关。三地区中菜田中憎水性物质与亲水性物质比例分别为0.30、0.39、0.41,反映了菜田中存在着不同程度的腐殖化现象。总之,农田转变为菜田后,显著影响了DOC的数量和质量。

Effect of land use on the composition of soildissolved organic carbon

Soil samples were collected from croplands and vegetable lands in Quzhou County of Hebei, Shouguang County of Shandong and Shunyi District of Beijing for comparison between lands under two different patterns of land use at the same location in content, distribution in the soil profile and composition of DOC. Results show that in the topsoil soil organic carbon (SOC) was 3.16 ~ 47.4% higher and total Nitrogen (TN) 3.09 ~ 64.1% higher in the vegetable fields than in the crop fields, while soil C/N and pH lower. The DOC content in either crop or vegetable fields decreased significantly with soil depth. The mean of the DOC contents in the topsoils of the vegetable fields was 1.70 times as high as that of crop fields. A significantly positive relationship was observed between SOC and DOC. In terms of composition of the DOC, its fractions followed an order of Hydrophilic matter (HIM) > Hydrophobic acids (HOA) > Hydrophobic neutrals (HON) > Hydrophobic bases (HOB) in the top soil (0~30 cm) in both crop fields and vegetable fields. In vegetable fields, HOA accounted for 19.0~26.7%, while in crop fields for 14.83~16.42%; The difference between the two fields in Shouguang was quite significant (p<0.05), which is probably related to the higher SOC contents and lower pH in its vegetable field. The HOM/HIM ratio was 0.30, 0.39 and 0.41 in the vegetable fields of the three regions, which may suggest that the vegetable fields vary in humification degree. In conclusion, transformation of crop fields into vegetable field significantly affects quantity and quality of DOC.