岩溶区不同土地利用方式对土壤有机碳及其组分的影响

Effects of Land Use Types on Soil Organic Carbon and Its Fractions in Karst Area

选择重庆市中梁山岩溶槽谷中5种土地利用方式（弃耕地、草地、菜地、橘园地和林地）为研究对象,在野外调查和室内分析的基础上,采用方差分析法对比分析了土壤总有机碳、溶解性有机碳、易氧化性碳、轻组有机碳、颗粒有机碳及矿物结合态有机碳的含量变化,并用相关分析法分析了土壤有机碳各组分之间的关系.结果表明：不同土地利用方式土壤总有机碳（TOC）含量随土层深度增加而降低,上下层土壤TOC含量在2.69～13.88 g/kg之间,不同植被覆盖类型、耕作方式和施肥是影响土壤TOC分布的重要因素.不同土地利用方式下有机碳各组分（DOC、EOC、LFOC、POC和MOC）含量在垂直分布上均呈现出随土壤深度的增加而降低的趋势,但不同土地利用方式之间的差异较大,主要与植被类型、施肥管理、耕作方式以及人为干扰有关.弃耕地含量均比较低,林地和草地受人为干扰较少含量较高,菜地土壤受施肥和翻耕影响,上下层土壤含量差异不大,橘园地上下层土壤5种有机碳组分含量差异均是最大的.弃耕地受之前耕作影响,弃耕时间短,有机质输入量少,POC/MOC值相对较低,菜地受施肥和翻耕影响上下层土壤POC/MOC值相对比较稳定,草地、橘园地和林地0-20 cm土壤POC/MOC值均高于20-40 cm,下层土壤有机碳比较稳定.0-20 cm和20-40 cm土壤有机碳及组分之间存在相关关系,0-20 cm土壤TOC与LFOC和MOC之间呈显著正相关,LFOC与POC之间也呈现显著正相关;20-40 cm土层,土壤TOC与EOC、LFOC和MOC之间呈显著正相关性,MOC与TOC以及EOC和LFOC均呈现正相关性,LFOC与POC之间关系由表土层的显著正相关转变为极显著正相关.下层土壤比上层土壤有机碳稳定性强,尤其是土壤TOC、LFOC和MOC能够敏感地反映土壤碳库的变化,可以作为土壤有机碳稳定性的敏感性指标.

Based on field investigation and laboratory analysis, this study investigated the contents of total organic carbon（TOC）, dissolved organic carbon（DOC）, easily oxidized organic carbon（EOC）, light fraction organic carbon（LFOC）, particulate organic carbon （POC） and mineral-associated organic carbon （MOC） in soil under 5 land use types（abandoned land, grassland, vegetable field, citrus orchard and forest land） in Karst Valley of Zhongliang Mountain in Chongqing. Variance analysis was applied to compare the contents of soil organic carbon under different land use types and correlation analysis was used to analyze the relationship between soil organic carbon fractions. The results showed that TOC content in soil under different land use types decreased with the increasing soil depth, which ranged from 2.69 g/kg to 13.88 g/kg in topsoil and subsoil. The vegetation type, cultivation method and fertilization significantly affected the distribution characteristics of TOC. Under different land use types, the contents of different organic carbon fractions （DOC, EOC, LFOC, POC and MOC） showed similar vertical distribution, which reduced with the increasing soil depth. However, soil organic carbon contents significantly differed under different land use types, which were mainly related to vegetation type, management of fertilization, cultivation method and human disturbance. The contents of different soil organic carbon fractions were all very low in abandoned land, while quite high in forest land and grassland because of the absence of human disturbance. Due to the fertilization and ploughing in vegetable field, soil organic carbon contents did not obviously differ in topsoil and subsoil of vegetable field, while the contents of 5 organic carbon fractions all significantly differ in topsoil and subsoil of citrus orchard. The abandoned land was affected by the previous cultivation and the time after land abandoning was short. Therefore, the input of organic matter was very limited and the ratio of POC/ MOC was relatively low in abandoned land. Since vegetable field was affected by fertilization and ploughing, the ratio of POC/MOC in the topsoil and subsoil of vegetable field was relatively stable. In grassland, citrus orchard and forest land, POC/MOC in 0-20 cm of soil were higher than that in 20-40 cm of soil, with the organic carbon contents in subsoil were more stable than those in topsoil. Significant correlations were observed between the contents of organic carbon fractions in 0-20 cm and 20-40 cm of soil. In 0-20 cm of soil, positive relationships existed between TOC and LOFC, TOC and MOC, and between LFOC and POC. In 20-40 cm of soil, significant positive correlations were found between TOC and EOC and between MOC and LFOC. EOC and LFOC, as well as TOC and MOC, were positively correlated. The positive relationship between LFOC and POC was more significant in 20--40 cm of soil than in topsoil. The results indicated that the stability of organic carbon increased from subsoil to topsoil. In particular, TOC, LFOC and MOC could reflect changes in soil carbon pool, which can be used as the sensitive indicators to indicate soil organic carbon stability.