Earthworm diet related to soil organic matter dynamics through 13C measurements.

The ability of earthworms to assimilate soil organic pools of different ages was investigated in field conditions through natural 13C labelling. Provided that 13C natural abundance of earthworm tissues is determined by their diet, the assimilation of soil organic matter by earthworms was estimated by measuring 13C/12C ratio of tissues of earthworms sampled in soils containing organic pools with differing 13C/12C ratios. Earthworms were collected in two locations where the vegetation shifted from a C3 to a C4 type (France), or from a C4 to a C3 type (Ivory Coast) 3 to 20 years ago. The results show that irrespective of their ecology (litter or soil-feeding), earthworms mainly feed on recent soil organic pools and assimilate soil organic matter with the same age distribution as the overall decomposers in the soil.