不同林型兴安落叶松林土壤团聚体及其有机碳特征

【目的】团聚体是土壤结构的基本单元,其对有机碳的保护作用是稳定土壤碳库的重要机制。采用野外调查与室内分析相结合的方法,探讨林型对兴安落叶松林土壤团聚体的分布、稳定性及有机碳含量的影响,为兴安落叶松林的可持续经营、碳汇功能提升提供参考。【方法】在内蒙古大兴安岭兴安落叶松原始林内,依据不同林型(草类-兴安落叶松林、杜香-兴安落叶松林和杜鹃-兴安落叶松林)设置28块30 m×30 m的样地,以距地面0~10 cm、≥10~20 cm、≥20~40 cm和≥40~60 cm分层取土样,测定土壤理化指标、不同粒径土壤团聚体及有机碳含量;基于单因素方差分析、相关分析和逐步回归分析方法,分析各林型间土壤团聚体各特征值的差异,以及各土壤理化指标对土壤团聚体分布、稳定性及有机碳含量的影响,筛选对各林型土壤团聚体有显著影响的主导因子。【结果】①兴安落叶松林土壤团聚体含量以粒径≥0.250~2.000 mm团聚体占比最高,且表层(0~10 cm)含量显著大于其他各层;各林型土壤大团聚体(粒径≥0.250~2.000 mm)含量大小表现为杜鹃-兴安落叶松林>草类-兴安落叶松林>杜香-兴安落叶松林,林型对20 cm以下土层各粒径的团聚体含量影响显著。②兴安落叶松林表层(0~10 cm)土壤的团聚体稳定性较高,其平均质量直径(MWD)和几何平均直径(GMD)显著大于其他各层,但各林型间无显著差异;稳定性指标在各林型间的显著差异主要发生在≥40~60 cm土层,杜鹃-兴安落叶松林土壤团聚体的稳定性较好。③各林型土壤团聚体有机碳含量由多到少依次为粒径≥0.250~2.000 mm团聚体、粒径<0.053 mm团聚体、粒径≥0.053~0.250 mm团聚体,各粒径均表现出杜香-兴安落叶松林的土壤团聚体有机碳含量最高;不同林型各粒径土壤团聚体有机碳含量均随土层深度增加而递减,递减速率随粒径大小依次减小,且具有明显的表聚特征。④土壤总有机碳是各林型粒径<0.053 mm和≥0.250~2.000 mm团聚体的共同主导因子,而粒径≥0.053~0.250 mm团聚体的主导因子因林型不同而存在明显差异。【结论】兴安落叶松林土壤团聚体及其有机碳含量均以大团聚体为主,林型对土壤团聚体的粒径分配和稳定性具有一定影响,其中,≥0.250~2.000 mm团聚体含量以杜鹃-兴安落叶松林的最高,<0.250 mm团聚体含量和各粒径土壤团聚体有机碳含量均以杜香-兴安落叶松林的最高。土壤理化性质对土壤团聚体的形成和稳定具有一定影响,不同林型的土壤团聚体主导因子存在差异;有机质是粒径≥0.250~2.000 mm土壤团聚体的主要胶结物质,而金属氧化物有利于<0.250 mm土壤团聚体的形成,土壤水分和养分含量高的酸性土壤有利于兴安落叶松林土壤大团聚体的形成和土壤结构的稳定。

Characteristics of the soil aggregate and its organic carbon in different Larix gmelinii forest types

【Objective】An aggregate is the basic unit of soil structure, and its protection of organic carbon is an important mechanism for soil carbon pool stabilization. The effects of forest types on the distribution, stability and organic carbon content of soil aggregates in Larix gmelinii forest were studied through the field investigation and laboratory analysis. 【Method】In the Larix gmelinii virgin forest in Greater Khingan Mountains in Inner Mongolia, 28 plots of 30 m× 30 m were set up according to different forest types (grass-Larix gmelinii, Ledum palustre-Larix gmelinii, and Rhododendron simsii-Larix gmelinii). The soil physicochemical indexes, soil aggregate content and organic carbon content of different particle sizes were determined by stratified samplings at 0-10 cm, ≥10-20 cm, ≥20-40 cm and ≥40-60 cm below the ground. Based on One-way ANOVA, the correlation analysis and stepwise regression analysis, the differences of soil aggregate characteristic values among different forest types and the effects of soil physicochemical indexes on distribution, stability and organic carbon of soil aggregates were analyzed, and the dominant factors that had significant influences on soil aggregates of different forest types were selected. 【Result】①The soil aggregate content in Larix gmelinii forest was the highest in particle sizes ≥0.250-2.000 mm and the content in the surface layer (0-10 cm) was significantly higher than that in the other layers. The macroaggregate content followed the order: Rhododendron simsii-Larix gmelinii > grass-Larix gmelinii > Ledum palustre-Larix gmelinii, and the forest type had a significant impact on the aggregate content of each particle size in the soil layer below 20 cm. ②The soil aggregate stability in the surface layer (≥0-10 cm) of Larix gmelinii forest was higher than that of the other layers with no significant difference among different forest types. The significant differences among different forest types mainly occurred in the layer of ≥40-60 cm, and the soil aggregate stability of Rhododendron simsii-Larix gmelinii forest was better than the other two forest types. ③ The organic carbon content of different particle sizes soil aggregates in different forest types was in the following order: (≥0.250-2.000 mm) aggregates, (<0.053 mm) aggregates, and (≥0.053-0.250 mm) aggregates. The organic carbon content of soil aggregates in the Ledum palustre-Larix gmelinii forest was the highest; the organic carbon content of soil aggregates in different forest types decreased as the soil layer depth increased, and its decline rate decreased as the particle size decreased and had obvious surface aggregation characteristics. ④The soil total organic carbon was the common dominant factor of ≥0.250-2.000 mm and <0.053 mm aggregates of the three forest types, while the dominant factors of ≥0.053-0.250 mm aggregates were significantly different across the forest types. 【Conclusion】The soil aggregates and their organic carbon contents of Larix gmelinii forest were mainly macroaggregates, and the forest type had a certain effect on the particle size distribution and stability of soil aggregates. The content of ≥0.250-2.000 mm aggregates in Rhododendron simsii-Larix gmelinii forest was the highest, and the content of <0.250 mm aggregates and the organic carbon content of soil aggregates in different particle sizes were the highest in the Ledum palustre-Larix gmelinii forest. The soil physicochemical indexes had influences on the formation and stability of soil aggregates, and the dominant factors of soil aggregates in different forest types were different. The organic matter was the main binding agent of ≥0.250-2.000 mm aggregates, while metal oxides were in favor of <0.250 mm aggregate formation. Acid soil with high soil moisture and nutrient levels are conducive to the formation of soil macroaggregates and the stability of soil structure in Larix gmelinii forest.