Soil faeces, springboard for SOM formation: what do we know and where do we go?

Dr Alix Vidal1, Dr. François-Xavier Joly2

1Tum – Chair Of Soil Science, Freising, Germany, 2University of Stirling – Biological and Environmental Sciences, Stirling, United Kingdom

Fragmentation of plant litter is one of the dominant pathways of litter decomposition and subsequent SOM formation. It is driven by a wide diversity of soil macrofauna (e.g., earthworms, millipedes, isopods, snails) that feed on litter and/or soil and egest faeces that present a complex architecture and composition. Although a large part of plant inputs is ingested by these animals during the decomposition process in many ecosystems, the characteristics and fate of these faeces remains poorly understood. We present recent advances depicting the chemical and physical characteristics of soil macrofauna faeces and exploring the factors regulating their fate in the soil over time. These advances point to a homogenisation of litter quality and increased lability following litter conversion into faeces, leading to faster decomposition rates and incorporation into the soil. This fragmentation pathway that results in the production of particulate OM, mineral-associated OM and/or dead bacterial residues, appears as a springboard for SOM formation. The evaluation of the importance of faeces in SOM formation emerges as a critical challenge requiring better understandings of (i) the consumption and assimilation of plant litter by soil animals to estimate how much litter enters the pathway, of (ii) the digestion and fragmentation of the litter to track the change in lability, and of (iii) the incorporation of these diverse faeces as SOM. In light of these results and remaining knowledge gaps, we present guidelines for future research investigating the fate of OM entering the fragmentation pathway. Addressing these knowledge gaps will require combining methods (e.g., imaging, bulk biogeochemical analyses) and disciplines (e.g., ecology, zoology, microbiology, soil science) at different time and spatial scales to tackle the interactions between plant residues, detritivores, microorganisms and mineral particles. Ultimately, this will allow incorporating the effects of soil macrofauna into SOM formation models and enhance their prediction accuracy.

Biography:  Dr. Alix Vidal, born 1989 in Epernay, France

7 ISI-papers with 39 citations, h-index is 4

Professional and academic career

  • since 2016 – Research Assistant (Akademischer Ratin auf Zeit), Chair of soil science, Technical University of Munich
  • Sep. 2016 – Dr. in Soil science, University Pierre et Marie Curie (UPMC), France
  • 2013 – 2016 – Doctoral candidate at UMR Metis, UPMC, France
  • 2013 – Dipl. Agricultural engineering, Ecole Supérieure d´Agriculture d´Angers, France
  • 2013 – Dipl. Agricultural engineering, Escola Superior de Agricultura « Luiz de Queiroz », São Paulo, Brazil
  • 2007-2013 – Study of agricultural engineering, France/Brazil

Research areas

  • Soil biogeochemistry
  • Biotic factors (litter type and earthworms) controlling soil organic matter decomposition
  • Interactions between plant, soil and microorganisms in the rhizosphere
  • Influence of organic amendments on soil characteristics
  • Use of carbon stable isotope (13C) to trace carbon flows in soils
  • Combination of classical quantitative (EA-IRMS, GC-MS, NMR spectroscopy) and spectromicroscopic (NanoSIMS) and imaging techniques (TEM, SEM)

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