The understanding of food webs in soil has lagged behind that of above-ground or aquatic systems because of the bewildering complexity of soil organism communities and the sheer intractability of making observations and doing experiments in soil. It has long been thought that invertebrates in forest soils derive most of their carbon from leaf litter that falls from trees. Pollierer et al. used a construction crane to alter the isotopic ratio of 13C and 12C supplied (as CO2) to the canopy of a Swiss forest. They then reciprocally transferred the resultant leaf litter to neighboring forest areas that had experienced a normal isotopic ratio of CO2, and measured the isotopic ratios in the tissues of soil animals. The carbon isotopic ratio in the invertebrates more closely matched that of the tree roots rather than that of the leaf litter to which they were exposed, indicating that the diet of these animals derived primarily from root tissue and exudates as compared to fallen leaves (which therefore appear to be processed largely by microorganisms). If this pattern extends to other temperate forests, the configuration of below-ground food webs and patterns of carbon flux might have to be reconsidered. -- AMS
Ecol. Lett. 10, 729 (2007).
