Effects of different earthworm densities on stability and organic carbon of soil aggregates in a Moso bamboo forest.

Abstract

Earthworms play a crucial role in regulating soil aggregates and soil organic carbon content. However, the effects of earthworm density on the composition, stability, and organic carbon of various soil aggregate fractions in Moso bamboo (Phyllostachys edulis) forest remain poorly understood. We conducted a 180-day in situ experiment to investigate the effects of different earthworm densities on composition, stability, organic carbon content of soil aggregates in a Moso bamboo forest. There were three treatments, including control (CK, no earthworm), local earthworm density (OE, 8 earthworms added in 50 cm×50 cm×40 cm), and double earthworm density (DE, 16 earthworms added in 50 cm×50 cm×40 cm). Compared to CK, the OE and DE treatments significantly increased the proportion of water-stable large macroaggregates (>2 mm) by 62.8% and 35.1%, respectively. Earthworm density improved soil aggregate stability, with stronger impacts of DE treatment than the OE treatment. Both OE and DE treatments increased organic carbon content across all soil aggregate fractions, with the organic carbon contents in bulk soil rising by 19.1% and 24.0%, respectively. Organic carbon contents in bulk soil were significantly correlated with the composition, stability, and organic carbon content of soil aggregates. Results of random forest analysis showed that organic carbon content in the bulk soil under the OE treatment was more strongly influenced by the organic carbon content in various soil aggregate fractions, whereas it was more strongly influenced by aggregate stabi-lity under the DE treatment. In conclusion, earthworms improved soil aggregate properties, thereby increasing organic carbon content in bulk soil, as indicated by the fact that higher earthworm densities promoted the formation of more aggregate organic carbon and enhanced soil aggregate stability.