A. Treonis, S. Grayston, & P. Murray

The effects of belowground root herbivory on soil processes and biota have not been studied extensively outside of the context of plant pathology.  Root grazing by macroinvertebrates, such as insect larvae, is a potentially important rhizosphere interaction affecting substrate quantity, quality, and spatial distribution in soils.  Root grazing by larvae has been shown to increase rhizosphere carbon flow through enhanced root exudation.  This effect is likely to have a strong influence on the structure of soil microbial communities in the rhizosphere.

The NERC Soil Biodiversity Thematic Programme is a five-year coordinated project whose objective is to increase understanding of biological diversity in soil and the functional roles played by soil organisms.  As part of this Programme, the impact of feeding by leatherjacket larvae (Tipula paludosa) on rhizosphere carbon flow and microbial communities was investigated in microcosm experiments, using soil from an upland grassland located in the Cheviot Hills, Scotland.  Microcosms were constructed to allow aseptic plant growth and collection of root exudates.  Bentgrass (Agrostis capillaris), ryegrass (Lolium perenne) and clover (Trifolium repens) were separately grown in microcosms with and without the presence of T. paludosa.  Larvae fed on roots, resulting in changes in the collected root exudates.  These exudates were supplied to soil in receptor microcosms through a drip mechanism.  After application of exudates to soils, changes in the metabolic profiles and structure of the soil microbial communities were assessed using community-level physiological profiling and PLFA.  The relevance of these changes to increasing our understanding of soil biodiversity and function in the rhizosphere are discussed.