Distribution patterns of the earthworm community in relation to soil properties and metals in agro-ecosystems in Hebei Province, North China

In this study, we examined the influence of soil variables (pH, total potassium (TK), available potassium (AK), total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), cation exchange capacity , soil organic carbon (SOC), moisture content (Moisture), subsurface temperature (TEMP), and metal concentrations (Cd, Pb, Cu, and Zn)) on the distribution patterns of earthworm ecological categories, diversity, and species composition in Hebei Province, North China. In total, 535 earthworms were collected from 18 sites, and belonged to three families, six genera, and ten species. Drawida gisti (17.9 inds m−2, 37.8%) and Amynthas hupeiensis (9.3 inds m−2, 39.5%) were the dominant species. The Co-inertia analysis ranking results among the soil factors and earthworms indicated that SOC and AK enhanced the earthworm density (R = 0.76**, p < 0.01; R = 0.77**, p < 0.01). The distribution patterns of epigeic and endogeic species appeared to follow an opposite trend to soil variables (SOC, K, and Moisture) under different agricultural management practices. Anecic species differed considerably from the other ecotypes, and were unaffected by the soil properties (except for TEMP) and metals. The redundancy analysis results showed that the abovementioned dominant species (D. gisti and A. hupeiensis) belong to ecological groups with different propensities for the soil factors (K, P, and SOC). Overall, the soil metal (Cd and Pb) concentrations were not the dominant regressors for the earthworm assemblage. Soil properties (K and SOC) were the main factors affecting earthworm density, category, and species dominance in the study areas.