三峡水库消落带不同土地利用对土壤团聚体稳定性及其碳氮分布的影响

Effects of Land-use Types on Soil Aggregate Stability and Organic Carbon and Nitrogen in Riparian Zone of Three Gorges Reservoir

团聚体稳定性是维持土壤生产力与土壤健康的关键因素,研究不同土地利用方式对团聚体稳定性及其碳氮分布的影响,对消落带生态环境的恢复与重建具有十分重要的意义。以三峡水库土质消落带3种典型的土地利用方式(玉米地、水田、撂荒草地)为研究对象,采用湿筛法测定0~10、10~25 cm土层团聚体粒径分布与团聚体稳定性,并测定全土及各粒径土壤团聚体有机碳、氮含量,利用结构方程模型(SEM)分析团聚体有机胶结物、土壤基本理化性质与水稳性团聚体稳定性的关系。结果表明:(1)三峡水库消落带中,土地利用方式在不同土壤深度对团聚体稳定性及其碳氮含量的影响不同;(2)0~10 cm土层中,农田撂荒后显著提升了土壤大团聚体比重与团聚体稳定性;撂荒草地的各粒径土壤团聚体有机碳、氮含量显著高于农田;>0.25 mm粒径团聚体有机碳、氮对全土有机碳、氮含量的相对贡献率显著提升;(3)10~25 cm土层中,农田撂荒后土壤团聚体及其有机碳、氮含量并没有得到明显改善;(4)结构方程模型分析发现,土壤有机碳(路径系数为0.76)与全磷(0.58)对团聚体的稳定具有显著的正面影响,pH(-0.42)对团聚体的稳定具有显著的负面影响,全钾(0.23)与全氮(0.15)通过促进土壤有机碳的形成而间接促进土壤团聚体稳定性,土壤容重(-0.11)通过影响土壤有机碳而间接削弱土壤团聚体稳定性。研究结果可为三峡水库消落带土壤结构稳定性评价及生态恢复规划提供理论依据。

Soil aggregate stability is a key factor of soil productivity and soil health.In order to provide a basis for the restoration and reconstruction of the ecological environment in the riparian zone,the distribution and stability of soil aggregates in different types of land-use,and the distributions of organic carbon and nitrogen in various aggregates,were explored.Of three typical land-use types(corn fields,paddy fields,and abandoned grasslands) in the riparian zone of the Three Gorges Reservoir,soils were classified using the wet sieving method.The distribution of aggregates and their organic carbon and nitrogen contents were clarified at soil profile depths of 0-10,10-25 cm for each land-use type.Additionally,the organic carbon and nitrogen content of the bulk soil and different soil aggregates fractions were measured.The relationships between organic cement of the aggregates,soil physicochemical properties and soil aggregate stability were analyzed by structural equation modeling(SEM).The results showed that:(1) Soil depths have different effects on aggregate stability,organic carbon and nitrogen content in the riparian zone of the Three Gorges Reservoir;(2) In the 0-10 cm soil layer,the proportion of soil macroaggregates and the stability of aggregates were significantly enhanced following farmland abandonment;soil aggregate carbon and nitrogen of different soil aggregates fractions in abandoned grasslands were significantly higher than that of farmlands;the relative contribution rate of organic carbon and nitrogen of >0.25 mm fraction aggregates to the bulk soil organic carbon and nitrogen content significantly increased;(3) In the 10-25 cm soil layer,soil aggregate stability,aggregate-associated carbon and nitrogen have been insignificantly improved following farmland abandonment;(4) Structural equation model analysis found that soil organic carbon(path coefficient of 0.76) and total phosphorus(0.58) had a significant positive effect on soil aggregate stability,and pH(-0.42) had a significant negative effect on soil aggregate stability;total potassium(0.23) and total nitrogen(0.15) indirectly promoted the soil aggregate stability via promoting the formation of soil organic carbon;soil bulk density(-0.11) indirectly weakened the soil aggregate stability by inhibiting soil organic carbon.All of the findings from this study may serve as theoretical bases for evaluating soil structure effects and ecological restoration.