重庆农田土壤有机碳稳定性同位素空间分布特征

Spatial Characterization of Stable Isotope Composition of Organic Carbon from Farmland Soils in Chongqing

对重庆182个典型农田土壤剖面有机碳稳定性同位素组成(δ^(13)C_(SOC))的测定结果表明,所有剖面土壤δ^(13)C_(SOC)值均随采样深度增加逐渐趋正,表、中和底层均值分别为(-23.63±1.53)‰、(-22.43±1.59)‰和(-21.42±1.90)‰.就地域而言,渝东北土壤δ^(13)C_(SOC)值偏负程度最高,渝中土壤则偏正.水田δ^(13)C_(SOC)值明显偏负,旱地偏正,水旱轮作则居中;三者表层土壤δ^(13)C均值分别为(-25.32±0.93)‰、(-23.17±1.37)‰和(-24.75±1.28)‰;不同类型土壤表层δ^(13)C均值依序为:水稻土<潮土<紫色土<石灰(岩)土<黄壤.回归树分析表明,表层土壤δ^(13)C_(SOC)值主要受作物类型控制,中底层则主要与土壤类型有关;其它因素如土壤性质(总氮、SOC和pH)和气象条件(降雨量和气温)等也有一定的影响.换言之,表层土壤稳定性碳同位素分布主要受碳源的影响,中底层主要与土壤碳循环过程有关.

Soil was sampled from 182 profiles in typical farmlands of Chongqing and analyzed for the stable carbon isotope composition of organic matter(δ^(13)C_(SOC)).The results showed that the values ofδ^(13)C_(SOC)for each soil profile were gradually increasing with increasing soil depth,and the mean values were(-23.63±1.53)‰,(-22.43±1.59)‰,and(-21.42±1.90)‰for surface,middle,and bottom layers,respectively.Theδ^(13)C_(SOC)values in the northeastern region of Chongqing tended to be more negative,whereas those in central Chongqing were less negative.Paddy fields showed the most negative values ofδ^(13)C_(SOC),followed by rice-upland rotating fields and upland fields,with the average being(-25.32±0.93)‰,(-23.17±1.37)‰,and(-24.75±1.28)‰for the surface layers,respectively.For different soil types,theδ^(13)C values in the surface layers were in the order of paddy soil<alluvial soil<purplish soil<calcareous soil<yellow soil.According to the regression-tree analysis,the crop types predominantly influenced the variation inδ^(13)C_(SOC)in surface soils,and soil types mainly affected that in the middle-and bottom-layer soils.Other factors,such as soil properties(TN,SOC,and pH)and meteorological conditions(precipitation and air temperature)played only minor roles in the variation ofδ^(13)C_(SOC).In short,the stable isotope composition of organic carbon in the surface soils was primarily controlled by the input carbon source,whereas that in the deeper layers was closely linked with carbon cycling processes within the soils.