Advancement in study on effect of earthworm on greenhouse gas emission in soil and its mechanism

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    Soil is an important source and sink, as well, of greenhouse gases (GHGs). Earthworms are a major component of the soil fauna, and a soil animal the highest in biomass in the soil. Being termed as soil ecosystem engineers, they play an crucial role in formation of soil physical-chemical properties and structure and in recycling of soil matter and nutrients through their feeding, burrowing and casting activities, thus directly or indirectly affecting the generation and emission of GHGs (CO2, N2O and CH4) in the soil. On one hand, the respiration of earthworm is an important part of soil respiration; in micro-environments, like guts, exudate, digesta and feces, anaerobic conditions, proper moisture content and rich C and N supply are favorable to growth and multiplication of denitrifying bacteria, thus greatly increasing biomass and activity of the bacteria, which in turn stimulates the emission of N2O during the process of denitrification (N2O 2.5~25 ng h-1 g-1 fresh earthworm), as is shown in recent studies. And N2O emission is higher from earthworm feces than from the soil in its surroundings. On the other hand, through feeding, burrowing and excreting, earthworms also cause changes in soil properties, composition and activity of soil microbes and some other ecological processes (e.g. decomposition, nitrification and denitrification), thus indirectly affecting GHGs emission. The activity of earthworms in the soil helps mix soil with plant residues and reshape soil pores and aggregates, thereby affecting soil moisture dynamics, aeration and content and availability of nutrients. Aerobic and anaerobic micro-environment within earthworm-made aggregates may also have some effect on decomposition and denitrification. Moreover, the macroaggregates formed by earthworms through their activities, in the long run, help C sequestration in microaggregates. Earthworms help blend plant residues with soil in their guts by feeding, thus expanding contact between microbes and organic matter, and alter composition and structure of the microbial community through their digestion and excretion processes. The interactions between earthworms and denitrifying and methanotrophic microbes cause formation of "drilosphere", where N2O emission increases and CH4 emission decreases. These effects are usually affected by soil moisture content, organic matter content and earthworm species. Based on their feeding and burrowing behaviors, earthworms are typically divided into three ecological groups: epigeic, endogeic and anecic species. Because of the differences in food accessibility and in distance the gases have to go through from the soil to the atmosphere, the three groups of earthworms differ sharply in ecological function, and the interactions between the groups make the effects on soil GHGs more complex. Besides, earthworm activities may also affect other soil fauna, such as mites, collembola, nematodes, isopods, enchytraeids, etc. in biomass and activity in their habitats. By the above-described indirect means, earthworms alter composition, structure and functions of the soil ecosystem. However, little is known about the effects of earthworm-plant interactions on GHGs balance in the soil. Besides, further researches are needed to fully understand interactions between different ecological groups of earthworms. To sum up, earthworms affect CO2, CH4 and N2O emissions mainly by regulating the ecological processes of carbon and nitrogen, such as decomposition, mineralization, nitrification, denitrification, methanogenesis and methanotrophy. Effects of earthworms on emission of GHGs have attracted more and more attention. Although much research has been done on the impacts of earthworms on soil CO2 and N2O emissions, little has been reported on CH4efflux. In view of the serious soil pollution problems, it is essential to unfold studies on changes in effects and potential role of earthworms in polluted soils. As for research techniques, current studies are still mainly based on short-term indoor incubation and simulation of one-factor environment. As the in-lab manipulated and simplified environments are far from good enough to reflect accurately the real conditions of the nature, it is urgent to start long-term in-situ field experiments and multi-environmental factor interaction experiments, because the functions of earthworm in the soil vary with the seasons; In addition, molecular and isotope tracing techniques have become available as effective tools for studies to expose biological and ecological mechanisms of earthworms’ effects on emissions of GHGs. It is essential, in future, to pay more attention to interactions of the different ecological groups of earthworms with soil properties, composition of soil microbes, other species of soil animals and plants growing on the surface of the soil, to intensify the study on mechanisms with stress on changes in earthworms’ function in polluted soils; to review comprehensively the effects of earthworms on emission of GHGs from the soil and carbon sequestration in the soil; to scientifically evaluate the effects of earthworm activities promoting or mitigating emissions of C and N from the soil.

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Lu Mingzhu, Wu Haitao, Lū Xianguo, Guan Qiang. Advancement in study on effect of earthworm on greenhouse gas emission in soil and its mechanism[J]. Acta Pedologica Sinica,2015,52(6):1209-1225.

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  • Received:April 17,2015
  • Revised:July 01,2015
  • Adopted:August 21,2015
  • Online: August 31,2015
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