Enchytraeid Community (Annelida, Clitellata, Enchytraeidae) and Its Dependence on Edaphic Conditions in Rice Agroecosystems in Russia

Communities of soil animals (meso- and macrofauna) in rice paddies tend to be fragmented, and have extremely low abundance. Nevertheless, some groups, such as enchytraeids, may become dominant in flooded conditions, as shown in tropical rice agroecosystems. However, the fauna and functional composition of enchytraeids (Annelida, Clitellata, Enchytraeidae) under such conditions have not yet been studied at temperate latitudes. We have investigated enchytraeid communities and the ratio of their functional groups in the main rice-growing regions of Russia: Krasnodar krai, Primorsky krai, and the Republic of Kalmykia. Samples were taken in summer–early autumn of 2016 in four habitat types: flooded rice paddies, drained paddies occupied by upland crops, adjacent bunds, and undisturbed grasslands (control). Generalized linear model analysis showed that the factor habitat type and its interaction with the factor region had a significant effect on the total enchytraeid abundance, with the factor region alone having no such effect. Their abundance was the highest in the control habitats and bunds (mean and standard error for all the regions: 3278 ± 1131 and 3255 ± 762 ind./m², respectively), being insignificantly lower in the paddies under upland crops (1282 ± 850 ind./m²) and decreasing to a minimum of 415 ± 323 ind./m² in the flooded paddies. A comparison between the last two habitat types shows that enchytraeids can relatively quickly restore their abundance in the rice paddies after draining. Principal component analysis revealed a positive correlation between the density of enchytraeids belonging to basophilous ecological group and bioavailable phosphorus content. The correlation between the abundance of acidophilous enchytraeids and this parameter was negative. Thus, the abundance ratio of enchytraeid ecological groups could be used as an informative indicator of the concentrations of nutrient elements and depends on physical and chemical characteristics of paddy soils. Despite the low abundance of enchytraeids in these soils, they can be an important component of the detrital food webs during periods of paddy-drainage in intensive rice agroecosystems at temperate latitudes.