Impact of root herbivory by insect larvae on soil microbial communities

Bentgrass (Agrostis capillaris) and clover (Trifolium repens) were grown as pure swards and mixtures in pots containing soil from the NERC Soil Biodiversity field site located in Scotland. Six weeks after plant establishment leatherjacket larvae (Tipula paludosa) were added at field density to half the pots and the impacts of their feeding on plant shoot and root biomass and soil microbial communities was determined after 10 days. Plate counts and community level physiological profiles (CLPP) were used to characterise the microbial communities. Larval herbivory had a significant negative effect on shoot growth of both grass and clover and root biomass of grass. In mixed swards, larvae preferentially fed on clover. Soil microbial community structure was altered in the presence of larvae with populations of pseudomonads being significantly increased. These community differences may be attributed to increased quantity and qualitative changes in carbon flux to the soil as a result of root herbivory, as indicated by differences in the CLPPs of microbial communities in the presence and absence of larvae. This was mainly due to increased utilisation of some sugars, carboxylic and amino acids in the presence of larvae.