【目的】 大兴安岭是我国唯一的寒温带地区,森林资源丰富,但大兴安岭地区土层较薄,且存在永冻层,对于该地区土壤结构、养分循环存在巨大影响。探讨该地区土壤团聚体的结构组成和有机碳、氮的含量与分布规律,了解不同粒径团聚体对土壤有机碳、氮的固存与保护作用,为深入研究我国寒温带地区土壤结构与碳氮循环提供依据。【方法】 在黑龙江大兴安岭地区,以我国寒温带4种主要森林类型(兴安落叶松林、樟子松林、山杨林、白桦林)为研究对象,测定生长季林地0~5、≥5~10和≥10~20 cm土层粒径<0.053、≥0.053~0.250、≥0.250~0.500、≥0.500~1.000和>1.000 mm水稳性团聚体的分配比例并结合有机碳、氮含量,分析各粒径团聚体有机碳、氮对土壤总有机碳、全氮的贡献率,进行多因素方差分析。【结果】 ①樟子松林、山杨林和白桦林0~10 cm土层和兴安落叶松林0~5 cm土层以大团聚体(粒径≥0.250 mm)为主,占50%以上,随着土层的加深,大团聚体质量分数下降,各个林型生长季中期大团聚体质量分数均高于初期和末期,且阔叶林大团聚体质量分数高于针叶林。②团聚体有机碳含量与全氮含量呈现出大致相同的变化规律,4种森林类型以粒径≥0.500 mm团聚体有机碳、全氮含量较高,大致表现为随粒径的减小含量递减。阔叶林团聚体有机碳、全氮含量比针叶林的高,且阔叶林的在生长季中后期含量相对较高,而兴安落叶松林的呈波动式变化趋势,樟子松林的则以生长季前期含量较高。③4种森林类型0~10 cm土层,团聚体有机碳、全氮以粒径≥0.500 mm团聚体贡献率较高,最高达到90%;随着土层的加深,≥0.250 mm的大团聚体的贡献率下降,≥10~20 cm土层以粒径<0.250 mm的微团聚体贡献率最高。④森林类型、土层和月份对土壤团聚体组成和团聚体有机碳、全氮含量均具有显著影响,且粒径≥0.500 mm团聚体有机碳、全氮含量与对应粒径团聚体含量呈正相关,粒径>1.000 mm团聚体有机碳、全氮含量与该粒径团聚体含量呈极显著正相关。【结论】 森林类型、土层和月份的变化均对土壤团聚体组成及其结合的有机碳、全氮含量产生影响,阔叶林大团聚体含量以及团聚体结合的有机碳氮含量均高于针叶林。4种森林类型以生长季中期大团聚体含量更高,阔叶林团聚体有机碳、全氮含量在生长季中后期较高,针叶林则在生长季内呈波动式变化趋势。随着土层的加深,大团聚体含量、团聚体有机碳、全氮含量以及大团聚体贡献率均逐渐降低。本研究区粒径≥0.500~1.000 m和>1.000 mm团聚体是有机碳和全氮的主要载体。由此可见,寒温带4种森林类型团聚体组成及其结合的有机碳、全氮特征各异,在一定程度上反映了寒温带主要森林类型下的土壤结构与碳氮固存特征。

【Objective】 The Greater Khingan Mountains area is the only frigid temperate region in China with abundant forest resources; however, in the Greater Khingan Mountains, the soil layer is thin and permafrost exists. The Greater Khingan Mountains has a great influence on the soil structure and nutrient circulation in this area. The structure and composition of the soil aggregates, and the content and distribution of organic carbon and nitrogen in this area were discussed. Further, the effects of aggrgates with different particle sizes on the retention and protection of organic carbon and nitrogen in the soil were understood, which provided a theoretical basis for further study of soil structure and the carbon-nitrogen cycle in frigid temperate regions of China.【Method】 In the Greater Khingan Mountain area of Heilongjiang Province, four main forest types in the frigid temperate zone of China (Larix gmelinii, Pinus sylvestris var. mongolica, Populus davidiana and Betula platyphylla) were studied. In the growing season, we determined the proportions of water-stable aggregates with particle sizes of >1.000, ≥0.500-1.000, ≥0.250-0.500, ≥0.053-0.250 and <0.053 mm, as well as the contents of organic carbon and nitrogen bound by aggregates in the soil layers of 0-5, ≥5-10 and ≥10-20 cm. The contribution rates of organic carbon and nitrogen to total soil organic carbon and total nitrogen were analyzed, and multi-factor analysis of variance was performed.【Result】 ① The 0-10 cm soil layer of Pinus sylvestris var. mongolica, Populus davidiana and Betula platyphylla, as well as the 0-5 cm soil layer of Larix gmelinii, were dominated by macroaggregates (≥0.250 mm), accounting for more than 50% of the soil. However, as the soil deepens the macroaggregate content declines. The macroaggregate content in the middle of the growing season of each forest type was higher than that in the early and late growth seasons, and the content of macroaggregates in broadleaved forests was higher than that in coniferous forests. ② The organic carbon and total nitrogen contents of the aggregates showed roughly the same change rule. The contents of organic carbon and nitrogen in aggregates with a diameter of ≥0.500 mm were higher in the four forest types, which showed a decrease as the size decreased. The content of organic carbon and nitrogen in the aggregates of broadleaved forests was higher than that of coniferous forests. The content of broad-leaved forest is also higher than that of coniferous forest in the middle and late growing season, whereas the deciduous pine forest of Larix gmelinii showed a fluctuating trend, and the Pinus sylvestris var. mongolica had higher content during the early growth season. ③ In the 0-10 cm soil layer of the four forest types, the contribution rate of organic carbon and nitrogen aggregates with a ≥0.500 mm particle size to soil total carbon and nitrogen was high, up to 90%. As the soil layer deepened, the contribution rate of macroaggregates decreased and the contribution rate of aggregates of <0.250 mm in the ≥10-20 cm soil layer was the highest. ④ The forest types, soil layers, and time of year had significant effects on the composition of soil aggregates, as well as the organic carbon and total nitrogen contents of aggregates. Moreover, the contents of organic carbon and nitrogen in aggregates with a ≥0.500 mm particle size were positively correlated with the contents of the aggregates of the corresponding particle size. Further, the contents of organic carbon and nitrogen in aggregates with a >1.000 mm particle size were significantly and positively correlated with the contents of the aggregates of the corresponding particle size.【Conclusion】 Changes in forest type, soil layer, and month all have an impact on the composition of soil aggregates, and their combined organic carbon and nitrogen content. The content of macroaggregates, along with the contents of organic carbon and nitrogen in macroaggregates in broadleaved forests were higher than those in coniferous forests. Depending on the month, four forest types had higher concentrations of macroaggregates in the middle of the growing season, the contents of organic carbon and nitrogen in broadleaved forest aggregates was higher in the middle and late growing seasons, and the coniferous forest showed a fluctuating trend during the growing season. With the deepening of the soil layer, the contents of macroaggregates, organic carbon, nitrogen and the contribution rate of macroaggregates all decreased gradually. Aggregates measuring >1.000 and ≥0.500-1.000 mm in size were the main carriers of organic carbon and total nitrogen in the study area. Thus, it can be seen that the aggregate composition and the combined organic carbon and nitrogen characteristics of the four forest types in the frigid temperate zone are different. To some extent, this reflects the soil structure, and the carbon and nitrogen fixation characteristics of the main forest types in the frigid temperate zone.