Earthworm Cast Formation and Development: A Shift From Plant Litter to Mineral Associated Organic Matter

Influence of earthworms on apolar lipid features in soils after 1 year of incubation

“…High Clab for hopene confirms intense assimilation of 13 C-labelled carbon by soil bacteria, which activity was probably stimulated by the deposition of undegraded 13 Cresidues onto the mesocosms at the beginning of the experiment. These results obtained from 20 g of soil or cast samples, also substantiate observations by nanoSIMS of 13 C-labelled bacteria on few µg of samples from same mesocosms (Vidal et al 2016b(Vidal et al , 2019. High incorporation of 13 C-labelled carbon in this bacterial biomarker further provides molecular evidence that microorganisms are key recyclers of plant OM in soils.…”

“…As a result, this one-year experiment support bacteria and other microorganisms as substantial source of OM in soil as acknowledged for a few years (Schaeffer et al 2015;Kögel-Knabner 2017). Hopene corresponds, at least partly, to the degradation product of more functionalized hopanoids (Innes et al 1997;Peters et al 2005) and several bacterial remains were identified through microscope examination of the present samples (Vidal et al 2019). Hence, hopene is probably typical of both bacterial living biomass and necromass, at least for the present mesocosms.…”

“…The proportion of C derived from the labelled residue results from the balance between residue incorporation and its degradation in the sample. Previous chemical and microscopic characterizations of earthworm casts from the same experiment showed that they underwent two distinct transformation phases (Vidal et al 2016a;2019): (1) a phase dominated by plant residue incorporation during the first two months and then (2) a phase marked by decomposition of plant OM and formation of organomineral associations. Additionally, above OEP calculation showed that alkanes were less degraded in casts than in the surrounding soils.…”

“…Hence, hopene is probably typical of both bacterial living biomass and necromass, at least for the present mesocosms. As OM degradation is the dominant process in the mesocosms after one-year incubation (Vidal et al 2016a(Vidal et al , 2019, higher Clab for hopene than alkanes further suggests less degradation and better preservation of bacterial living biomass and necromass than initial plant OM. In other words, these results tend to support that on the year-scale, organic carbon may be efficiently sequestrated in soils as bacterial necromass (Liang and Balser 2011;Miltner et al 2012).…”

Editorial: Elucidating Microbial Processes in Soils and Sediments: Microscale Measurements and Modeling

“…A group of 50 researchers from 7 different countries gathered for 3 days (Figure 2), and actively debated about the status of the research, about impediments to its necessarily interdisciplinary character, and about plans for future research activities. A very positive outcome of the workshop is that several researchers from different institutions have decided to collaborate on joint projects (e.g., Vidal et al, 2019). A follow-up MicroSoil Summer school will take place in June 2019, again in Saint Loup Lamairé, and another workshop, MicroSoil 2020, similar to the 2018 one, will be held there in June 2020.…”