成都典型区水稻土有机碳组分构成及其影响因素研究

农田生态系统土壤有机碳对农业生产、生态平衡和全球气候变化至关重要,有机碳组分构成及平均驻留时间对深入了解土壤有机碳特征及演变规律意义重大。通过土壤呼吸培养实验和三库一级动力学方程,模拟分析了成都典型区水稻土有机碳组分构成特征;利用土壤定量化属性与有机碳各组分相关及回归分析,建立研究区土壤有机碳各组分预测模型。结果表明,有机碳组分的活性碳、慢性碳和惰性碳含量在表层(0~20 cm)分别为0.42、6.13、11.43 g kg-1,均高于亚表层(20~40 cm)的0.23、4.09、7.50 g kg-1,两土层间有机碳组分含量具有显著性差异,但有机碳组分比例没有显著性差异。剖面(0~100 cm)有机碳组分含量随着深度增加而减小,活性碳和慢性碳比例随着深度增加而降低,惰性碳比例则随着深度增加显著升高。容重、全氮和全磷对有机碳各组分含量,质地对活性碳组分含量、比例及平均驻留时间,p H对慢性碳和惰性碳组分比例均具有显著影响;活性碳和惰性碳组分含量与土壤全氮、碳氮比、p H以及土壤细粉粒(0.02~0.002 mm)含量间存在显著线性关系,可用来预测水稻土有机碳各组分含量,研究结果对其他地区土壤有机碳各组分研究及预测具有积极启示作用。

Composition of organic carbon in paddy soil in typical area of Chengdu and its influencing factors

Soil organic carbon (SOC) in farmland ecosystems is essential to agriculture and crucial to ecology and global climate change. Composition and mean residence time (MRT) of SOC are closely related to soil structural stability, sustainable soil nutrient supply, soil biodiversity and mitigation of greenhouse effect. Based on the three-pool first-order kinetics equation and the soil respiration incubation experiment conducted, the major organic carbon components of the paddy soil typical of Chengdu were measured for analogical analysis of SOC composition and for establishment of models for prediction of SOC components by means of quantification of soil properties as well as correlation and regression analyses of various fractions of organic carbon. Results show that the content of active carbon (Ca), slow carbon (Cs) and resistant carbon (Cr), was 0.42 g kg-1 6.13 g kg-1 and 11.43 g kg-1, respectively, in the surface layer (0~20cm), and 0.23g kg-1, 4.09g kg-1 and 7.50g kg-1, in the sub-surface layer (20~40cm). Obviously, the contents were higher in the surface layer than that in the sub-surface layer. Although the organic carbon in the sub-surface layer was higher than that in the surface layer in inertness, no significant difference was observed between the organic carbons in the two soil layers in proportion of components. No apparent difference was observed either between paddy soils derived from similar parent materials but sorted into different subgroups in content and proportion of organic carbon components. However, soil texture had some high impacts on content and proportion of organic carbon components in the sub-surface layer. In soil profiles (0~100cm), contents of Ca and Cs decreased with increasing depth. However the decrease in content of Cr varied with soil subgroup, in some subgroups it decreased with soil depth, while in some it decreased first and then increased. In paddy soils the constituent proportions of Ca in all soil layers were less than 4% and no obvious change was found with soil depth; the constituent proportion of Cs was lower than that of Cr, and the two fractions of organic carbon varied with soil depth symmetrically, in constituent proportion, that is, Cs decreased with soil depth, while Cr increased significantly with soil depth. Paddy soils and forest soils shared some common characters in distribution of contents and constituent proportions of organic carbon components in soil profile, however, paddy soils, different in subgroup, had something common and something different, as well, in this aspect. Composition of soil organic carbon in paddy soils was subject to the integrated effect of bulk density, texture, particle-size composition, pH, carbon-nitrogen ratio, total nitrogen, total phosphorus, and total potassium, but each fraction of SOC had its own main affecting factors. The analysis results show that the contents of various organic carbon components were in extremely significant negative relationships with bulk density, and in extremely significant positive relationships with total nitrogen and total phosphorus. Clay was favorable to preservation of Ca, and weak alkaline environment was conducive to soil carbon sequestration. Based the relationships of the fractions of organic carbon with various related factors, the significant linear relations (R2= 0.69) observed of Ca with total nitrogen and pH and the significant linear relations(R2= 0.70) of Cr with soil total nitrogen, carbon-nitrogen ratio, pH value as well as the content of fine silt (0.02~0.002mm), it is feasible to predict contents of various fractions of organic carbon in paddy soil, but the prediction accuracy needs to be improved. However, the findings of this study has some positive reference value to researches and prediction of components of SOC in other regions.