Elemental Cycling

The biochemical transformation of oak (Quercus robur) leaf litter consumed by the pill millipede (Glomeris marginata)

Soil macrofauna play an essential role in the initial comminution and degradation of organic matter entering the soil environment yet the chemical effects of digestion on leaf litter are poorly understood at the molecular level. This study constituted part of a University of Bristol PhD research project that was undertaken to test the hypothesis that the biomolecular content of macroinvertebrate faeces (early soil organic matter) is determined as a direct consequence of the dietary requirements of the consumer organism. A number of pill millipedes (Glomeris marginata) were fed oak leaves (Quercus robur) after which the biomolecular content (lipids and macromolecular components) of dried oak leaves and millipede faeces was assessed using GC/MS and py-GC/MS maintained by NERC LSMSF.

It was found that short chain n-alkanoic acids, sterols and triacylglycerols fall dramatically in concentration in the millipede faeces relative to the leaf litter (Figure 1). Hydrolysable carbohydrates and proteins both decreased significantly in concentration in the faeces, while similar yields of phenolic components were observed for the cupric oxidation of lignin although the oxygenated functions appear affected by passage through the millipede gut. This shows that the composition of fresh organic matter entering the soil is directly controlled by invertebrates feeding upon the leaf litter and as such they are key contributors to the early stages of diagenesis in terrestrial soils.

Partial GC-FID chromatograms of leaves and millipede faeces

Figure 1