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

Abstract

Greenhouse gas emissions (CO 2 , N 2 O, CH 4 ) and chemical, physical and microbiological properties (pH, macro and micronutrients, texture, moisture, exchangeable NH 4 + , NO 3 − , 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 noningested 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 NH 4 , Cu, Fe and Mn contents, lower microbial biomass C and higher metabolic quotient (qCO 2 ), but with few differences in CO 2 , N 2 O and CH 4 emissions compared with noningested 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 N 2 O and CH 4 and confirming previous results observed using gut contents. The high exchangeable NH 4 and H 2 O contents influenced the oxyreduction 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.

Chemical composition of earthworm casts as a tool in understanding the earthworm contribution to ecosystem sustainability - a review

“…However, the pool of TOC and N t in the soil can increase in adequate situations of soil management, like revegetation (Zhang et al 2020) or exploitation of the bio-ecological features of soil biota, such as earthworm presence in soil (Padmavathiamma et al 2008), among others. Regarding this last aspect, an "earthworm dilemma" (Lubbers et al 2013) requires to be more investigation in the future by the scientific community: are the earthworms greenhouse emitters (Rizhiya et al 2007, Namoi et al 2019, Santos et al 2021 or, on the contrary, these organisms are carbon stockers (Zhang et al 2013)? An answer based on the achievements of the current research in the field indicates that this depends on site-specific conditions of the ecosystem (Knowles et al 2016, Thomas et al 2020, Puche et al 2022 or on other indirect factors like food substrate (Namoi et al 2019).…”