Background The stability of soil aggregates, the basic units of soil structure, is a key property for many soil ecological processes and functions such as soil and water conservation and soil carbon sequestration potential. The stability of aggregates is strongly correlated with labile carbon, and soil aggregation is mainly affected by labile organic carbon. The periglacial landform of eastern Liaoning is experiencing severe soil erosion and loss of soil fertility due to its special geological conditions. This study aims to reveal the stability of soil carbon and its regulation mechanism.

Methods In June 2019, about 1 kg of undisturbed soil blocks were collected at depths of 0-10 cm at 4 vegetation types(mid-mountain grassland, natural secondary forest, larch plantation and riparian grassland) according to elevations in periglacial landforms in the mountain areas of eastern Liaoning. Aggregate distribution and stability were determined using dry-sieving methods: 2.000, 1.000, 0.250 and 0.038 mm mesh sieves from top to bottom. After separation, the fractions of the aggregates were dried at 60 ℃ and then weighed. SOC(soil organic carbon) was determined by the digestion method with K₂Cr₂O₇-H₂SO₄. Labile organic carbon was determined by the oxidation of 333 mmol/L KMnO₄.

Results The content of labile organic carbon in the soil aggregates with particle size >2.000, >1.000-2.000 and >0.250-1.000 mm of different vegetation types was basically the same, showing the following order: mid-mountain grassland > natural secondary forest > larch plantation > riparian grassland, decreasing with altitude. The contribution rate of soil aggregate liable organic carbon decreased with aggregate size in mid-mountain grassland, natural secondary forest and larch plantation. Nevertheless, the contribution rate of labile organic carbon within aggregate size >0.25 mm was higher, and the contribution rate of >0.038-0.250 mm was lower. The linearly positive correlation was found between content of the soil aggregate labile organic carbon and total organic carbon. And the correlation between soil aggregate labile organic carbon and total organic carbon was more significant at the larger size. Soil aggregate organic carbon, labile organic carbon and non-labile organic carbon were positively correlated with vegetation coverage, litter biomass, root biomass and Eh, and negatively correlated with soil total nitrogen, bulk density, pH and water content.

Conclusions The characteristics of liable organic carbon in soil aggregates are mainly affected by vegetation characteristics, and soil physical and chemical characteristics were caused by vegetation type and temperature change-driven elevational changes. Therefore, more attentions should be paid to the impact of vegetation change and climate warming on soil carbon pool of periglacial landform in eastern Liaoning. The results of this study may provide a reference for the regulation of soil carbon pool stability in periglacial landforms in the mountain areas of eastern Liaoning.