Dawson, Grayston, Murray, Ross, Pratt, Cook, Gange, Treonis, Currie

The availability of carbon (C) is a key feature in controlling nutrient cycling in soil. In grassland, continual root turnover develops rich animal and microbial communities, while root browsing by invertebrates can increase the rate of turnover of root material and alter C and N flow in these systems.

The larval stage of Tipula paludosa has been identified as a dominant root herbivore at the experimental field site of the soil biodiversity project (http://www.macaulay.ac.uk/HUGBUG) (Sourhope, Scotland). Treatments of nitrogen and lime and insecticide (Dursban, one of the most common insecticides used to control T. paludosa in pasture) were applied to investigate management influences on C resources and soil biodiversity. The nitrogen and lime increased root growth while the insecticide application reduced root growth and the C and N input to the soil. The insecticide controlled larvae numbers, reduced tardigrade, nematode populations and altered the microbial community.

In laboratory experiments, larval herbivory generally had negative effects on plant growth, caused an increase in C return to the soil and altered the microbial community. The effects of root herbivory were species specific. Larvae preferentially fed on Trifolium repens, compared to Lolium perenne, and the root death rate was accelerated by herbivory more dramatically in T. repens. In contrast, larval herbivory of Agrostis capillaris had no effect on root system development or rhizosphere C flow. Through the use of complementary field and laboratory approaches we are developing a better understanding of the relationships between the root herbivore, plant species, C flow and soil biodiversity.

Acknowledgements

SEERAD (http://www.macaulay.ac.uk) and NERC soil biodiversity programme (http://mwnta.nmw.ac.uk/soilbio) are jointly thanked for funding this research.