Earthworms can variously affect soil properties and resource availability by feeding, burrowing, and casting activities. Figuring out the relationship among earthworms, soil and plant properties is beneficial for understanding the ecological functions of earthworms. Different densities of earthworms (high density, HDE; medium density, MDE; low density, LDE; control, CK) in soil columns were studied to reveal how earthworms influence soil physical and chemical properties and clover plant growth. The results showed that earthworms increased the large and medium aggregate content and decreased the microaggregate content. Soil aggregates in MDE were the most stable. Both the mean mass diameter (MWD) and geometric mean diameter of soil aggregates increased with the densities of earthworms. The average contents of soil organic carbon (SOC) in large-, medium-, and micro-aggregates were 5.5, 4.2, and 4.2 g kg-1 in the treatments with earthworms. There was a significant correlation between SOC content and macroaggregate organic carbon content. The root characteristic values of earthworm-treated clover were significantly higher than those of the control. The clover root indexes were positively correlated with the SOC content and soil aggregates. We considered that earthworms altered the soil aggregate contents and promoted soil organic carbon storage, and thus promote the development of vegetation roots. This study provides scientific supports for a deeper understanding of the mechanism of earthworms on soil carbon storage.

Soil degradation restricts the development of agriculture and the degree of soil degradation is related to land use type. Quick and efficient evaluation of the degree of soil degradation is needed for the timeous implementation of remedial measures to ensure soil sustainability. Earthworm community characteristics are closely related to soil management practices and soil quality and could be used for evaluation purposes. In this Loess Plateau study, the degree of soil degradation under nine different land use types (natural and planted woodland, shrubbery, and grassland, plus cropland, orchard, and abandoned land) was related to the earthworm community characteristics (density, biomass, and the Shannon-Wiener, Species richness, and Pielou’s evenness indices) using a soil degradation index calculated from soil physicochemical properties determined for each land use type. The earthworm community characteristics associated with a low degree of degradation were significantly higher than those associated with a high degradation degree. Compared to the artificially managed land use types, earthworms in the natural ones showed higher biomass, density, and diversity. The earthworm density, biomass, and Shannon-Weiner index were significantly correlated with soil organic matter and total nitrogen content. These findings indicate that earthworm community characteristics can comprehensively characterise the physicochemical properties and biological characteristics of soils under different land use types. Linear correlations showed a significant relationship between the soil degradation index and the earthworm community characteristics, indicating that the latter could be used effectively to evaluate and represent the degree of degradation of soils on the Loess Plateau over a certain degradation range.