Effects and mechanism of earthworms on soil organic carbon and nitrogen cycling: a review

Earthworms known as "ecological engineers", play an important role in shaping the structure of the soil system and affecting its function.More research has been focused on the effects of earthworms on soil physical and chemical properties, microbial communities change, organic matter decomposition and soil mineralization, while less attention is paid to their effects on the key processes of soil carbon and nitrogen cycling.This article reviewed the direct effects of earthworms through feeding, casting, burrowing activities and promoting the formation of soil aggregates, and indirect effects through influencing soil enzyme activities and microbial community composition on soil carbon and nitrogen cycling.The effects of earthworms on soil organic matter decomposition, nitrification and denitrification were also summarized.In the future, more attention should be paid to the establishment of quantitative models to assess the impact of earthworms on soil organic carbon pools, to systematically study the effects of the interaction of earthworms with microorganisms and other driving factors on the key processes of the carbon and nitrogen cycling, and to conduct multi-factor and multi-level research in combination with human activities.In the research method, the comprehensive application of isotope and molecular biology and other research methods, combined with indoor control and long-term field simulation experiments are required.