How ingested soil microbes stimulate greenhouse gas emissions and iron transformations of earthworms


From 04/2014 to 03/2019

Principal Investigator: Harold L. Drake, Marcus A. Horn
Staff: Oliver Schmidt

Earthworms are a dominant part of the soil fauna, are important to the structure and fertility of soils, emit the greenhouse gas nitrous oxide, and can influence and increase the emission of nitrous oxide from soils they inhabit. The in situ conditions of the alimentary canal (which includes anoxia and large amounts of high quality organic carbon) stimulate ingested soil microbes capable of anaerobiosis (e.g., denitrifiers that produce nitrous oxide). Work during the previous funding period demonstrated that (a) the capacity to emit nitrous oxide is variable but prevalent in diverse feeding guilds and in globally distributed earthworm families/species, (b) augmentation of anaerobiosis in the gut stimulates fermentation and methanogenesis and leads to the in vivo emission of molecular hydrogen and the greenhouse gas methane, respectively, by certain tropical earthworms, and (c) soil-derived iron is likely subject to microbial-linked redox processes during gut passage. Thus, various anaerobic processes facilitated by ingested microorganisms in the earthworm gut compete for available reductant during gut passage, and determine the profile of gases emitted by the earthworm and of products released in earthworm casts that contribute to soil chemistry. The goal of the new proposal is to elucidate microbial transformations of carbon, nitrogen, and iron during the passage of soil through the anoxic earthworm gut, processes that contribute to the cycling of elements in terrestrial ecosystems. The new objectives will focus mainly on tropical earthworms in Brazil and are to resolve: (a) key parameters impacting on the variable nitrous oxide emissions of earthworms, (b) the importance and origin of methane emitted by earthworms, (c) hydrogen emissions, gut fermentation profiles, and associated gut biota, and (d) iron-dependent redox processes and associated microbes along the alimentary canal. Both molecular and chemical analyses will be used to address these objectives

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