Field experiment reveals varied earthworm densities boost soil organic carbon more than they increase carbon dioxide emissions
Yufeng Qiu, Ronggui Tang, Yihong Liu, Youchao Chen, Yuye Shen, Shoujia Zhuo, Yanjiang Cai, Scott X. Chang
Abstract
• Earthworms boosted CO 2 emissions and SOC concentrations in bamboo forest soils. • Earthworm activity raised CO 2 emissions by elevating DOC and BG levels. • Higher earthworm densities resulted in lower soil CO 2 emissions. • Earthworms increased SOCD sixfold compared to their CO 2 -C emissions. Earthworms play crucial roles in regulating soil organic carbon (SOC) and greenhouse gas emissions in forest soils. Laboratory studies have proven that they promote soil carbon dioxide (CO 2 ) emissions. However, the effects of earthworm activity on forest soil CO 2 emissions and organic carbon (C) have not yet been quantified in situ, and the impact of different earthworm densities remain unclear. In this study, we investigated how earthworm ( Pheretima guillelmi ) activity at three densities (no earthworms, original density, and double the original density) affected SOC, its labile fractions, C-related enzyme activities, and soil CO 2 emissions in a Moso bamboo ( Phyllostachys edulis ) forest ecosystem over a six-month field experiment. Our results showed that the original earthworm density resulted in a 23.4 % increase in soil CO 2 emissions, while double the original earthworm density resulted in a 9.6 % reduction in emissions compared to the original density. Additionally, earthworms at both densities significantly increased the concentration of SOC and its labile fractions. Notably, the increase in SOC density (SOCD, SOC stock per unit land area, kg C ha −1 ) induced by earthworm activity far exceeded the increase in CO 2 -C emissions. Specifically, the earthworms at double the original density led to an 8.8-fold increase in SOCD, while the original density resulted in a 3.7-fold increase. Furthermore, our findings identified dissolved organic C (DOC) as the most critical labile organic C fraction influencing soil CO 2 emissions associated with earthworm activity, while β-glucosidase (BG) was the most significant C-related enzyme affecting soil CO 2 emissions driven by earthworm activity. These results provide important insights into the role of earthworms in both CO 2 emissions and SOC accumulation in subtropical forests.