乌兰布和沙漠东北部不同耕作年限农田土壤有机碳密度及其影响因素

明确干旱区农田开垦过程中土壤有机碳变化及其影响因素对评估其固存特征具有重要意义。本研究以乌兰布和沙漠东北部不同开垦年限(2～5、12～15、25～30、40～50年)农田为对象,以未开垦的自然土壤为对照,采用空间代替时间的研究方法,探究农田开垦过程中0～2 m土层内土壤有机碳密度变化特征及其影响因素。结果表明: 随开垦年限的增加,浅层(0～0.4 m)土壤有机碳密度呈持续增加趋势,但农田土壤有机碳密度均处于较低水平(0.990～1.983 kg·m^-2)。深层(1.2～2 m)土壤有机碳密度在开垦年限较长(25～30和40～50年)的农田中有所增加,而在开垦年限较短(2～5和12～15年)的农田中无增加趋势。未开垦土壤和各耕作年限农田深层土壤有机碳密度在0～2 m土层中占比较大(28.9%～38.6%)。不同耕作年限农田中土壤有机碳密度随土层深度的增加均呈先减小后增大的二次函数关系,且拟合度较高(R²为0.757～0.972)。土壤黏粒和粉粒含量是影响0～2 m土层有机碳密度的关键因素,且耕作年限对浅层(0～0.4 m)土壤有机碳的积累具有重要促进作用。

Soil organic carbon density and its influencing factors in croplands with different cultivation years in the Northeastern Ulan Buh Desert,China

Understanding the changes and influencing factors of soil organic carbon density (SOCD) during the conversion of uncultivated natural soil to croplands is of great significance for the assessment of carbon sequestration in arid areas. In this study, we compared SOCD in the uncultivated soil and that in croplands with different cultivation years (2-5, 12-15, 25-30, 40-50 years) in the Northeastern Ulan Buh Desert. The change of SOCD and its influencing factors at 0-2 m soil depth during the conversion of uncultivated natural soil to croplands were explored by the method of replacing time with space. The results showed that SOCD at the shallow soil depth (0-0.4 m) in croplands increased continuously with cultivation years, but basically at low levels (0.990-1.983 kg·m^-2). The SOCD at deep soil (1.2-2 m) increased in the croplands with longer cultivation years (25-30 and 40-50 years), whereas no obvious change trends in both the croplands with shorter cultivation years (2-5 and 12-15 years) and the uncultivated natural soil. The SOCD at deep soil (1.2-2 m) were relatively large (28.9%-38.6%) of the 0-2 m soil depth of uncultivated natural soil and croplands with different cultivation years. The vertical distribution of SOCD in croplands with different cultivation years were well fitted by quadratic functions (with R² ranging from 0.757 to 0.972). It was noteworthy that soil clay and silt contents had dominant influences on SOCD at all the soil profile (0-2 m), and that cultivation years mainly contributed to the accumulation of SOC at the shallow soil (0-0.4 m).