Emission of greenhouse gases and soil changes in casts of a giant Brazilian earthworm

Greenhouse gas emissions (CO2, N2O, CH4) and chemical, physical and microbiological properties (pH, macro and micronutrients, texture, moisture, exchangeable NH4+, NO3−, total C and N, organic C, microbial biomass C and metabolic coefficient) were monitored in casts of a large, endogeic native Brazilian earthworm species Rhinodrilus alatus and from non-ingested control soil incubated for up to 32 days. Earthworm casts represented a significantly different chemical and microbiological environment, with higher soil moisture, pH, H + Al, exchangeable NH4, Cu, Fe and Mn contents, lower microbial biomass C and higher metabolic quotient (qCO2), but with few differences in CO2, N2O and CH4 emissions compared with non-ingested control soil. Nonetheless, fermenting, methanogenic and nitrate-reducing microbes encountered ideal conditions for sustained anaerobic activity in the clayey, dense and moist castings of R. alatus, maintaining emission of N2O and CH4 and confirming previous results observed using gut contents. The high exchangeable NH4 and H2O contents influenced the oxy-reduction processes, affected GHG emissions and N transformations and modified soil microbial biomass and activity. In addition, selective ingestion concentrates C and N contents in the casts and transformation processes affect the availability of important plant nutrients, topics that deserve further attention, considering the widespread collection of this species for use as fish-bait in Brazil.