Earthworm-microbial interactions controlling nitrous oxide production in perennial grass- and legume- based agroecosystems using stable isotopes and molecular markers

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Earthworms are well known for their contribution to soil fertility and crop production. Agroecosystems with perennial vegetation, such as grass- and legume-based hayfields, support large earthworm populations because soils are undisturbed by cultivation and senescing plant residues are a food source for earthworms. Under these conditions, earthworm-created structures like surface and subsurface casts (fecal pellets), middens (soil-litter mixture at the soil surface) and burrows are numerous. These structures are a favorable habitat for microbial nitrifiers and denitrifiers that produce nitrous oxide, a potent greenhouse gas, as a byproduct of their metabolism. Previous laboratory studies by my research group have shown that earthworms stimulate nitrous oxide production, leading me to hypothesize that earthworm-microbial interactions lead to nitrous oxide production at small scales (microcosms, small field plots) and may contribute to seasonal nitrous oxide emissions at the agroecosystem level. These biological interactions will be evaluated with cutting-edge research tools, including 15N isotope dilution and DNA methods (q-PCR amplification of amoA, nosZ and other relevant genes, DNA-stable isotope probing). These advanced techniques tremendously increase our chance of discovering novel organisms and gaining new insights into microbially-mediated N transformations. Mathematical functions describing the earthworm-microbial relationships that contribute to nitrous oxide emissions from soils will be incorporated into predictive ecosystem-level models (DNDC, ecosys), which may eventually be used to calculate national greenhouse gas inventories with the IPCC Phase III methodology. In the next five years, this project will train 12 highly qualified personnel with specialized knowledge and analytical skills that are highly desired for research positions in the environmental sciences.