PARENT SESSION
Poster Session 30: Soil Ecology.

Wednesday, August 4 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.

Root herbivores, resource heterogeneity and root foraging behaviors interact to influence plant communities.

Stevens, Glen^*,1, Jones, Robert¹, ¹ Virginia Polytechnic Institute and State University, Blacksburg, VA, USA

ABSTRACT- There are potentially strong interactions between fine root herbivory, microsite fertility, and fine root growth that can lead to important tradeoffs for plant species. Plants that proliferate roots in nutrient-rich microsites (i.e., forage) in patchy environments can co-opt resources and grow larger than their competitors who forage to a lesser or minimal degree. However, if root herbivores forage in such patches also, heavily-foraging plant species may suffer greater losses to herbivory than their competitors. We designed a greenhouse experiment to examine these possible interactions. Three co-occurring perennial species (one grass, two herbs) were planted in greenhouse pots, two plants per pot, both in monoculture and mixed-species treatments. Mineral fertilizer was either spread uniformly over the pot, or concentrated into patches equidistant from plants. Root herbivores (white grub larvae) were collected in the field and added to randomly selected mixed-species pots. We predicted that the effect of grubs on plant biomass would be greater in heterogeneous than homogeneous conditions, and that a plant's tendency to forage would be associated with reduced yield where root feeders were added. After 4.5 months of growth, plants and grubs were harvested from the pots. Total aboveground biomass in pots varied significantly between species treatments (P < 0.0001), decreased significantly where grubs were added (P < 0.03), and increased significantly in heterogeneous conditions (P < 0.0001). Individual species differed significantly in their response to heterogeneity (P < 0.01). Combining all species, the impact of grubs on aboveground biomass was greater in heterogeneous pots as predicted. It appears that nutrient heterogeneity enhances the impact of root herbivory on plant growth.

Key words: Phyllophaga sp., rhizivory, root turnover