PARENT SESSION
Contributed Oral Session 166: Soil Communities and Plant-Root Interactions
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 522 A, Level 5, Palais des congrès de Montréal
Interactions between insect root herbivores and resource heterogeneity influence plant communities.
Stevens, Glen*,1, Jones, Robert1, 1 Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
ABSTRACT- Interactions between soil resources and roots in plant communities are typically studied without considering the role of insect root herbivory. Plant species differ in their tendency to proliferate roots in nutrient-rich patches (i.e., forage) in heterogeneous environments, and intensively-foraging species may be better competitors for limiting resources. However, if root herbivores preferentially forage in such patches, there may be a tradeoff between resource capture and exposure to root herbivory that influences competitive interactions. To investigate this issue, we designed field and greenhouse experiments using co-occurring herbs and trees, in which we manipulated patterns in resource availability and the presence of root-feeding Scarabaeidae larvae. In a greenhouse experiment designed to examine herbivore foraging behavior, we divided pots into four quarters: a fertilized, unplanted quarter, an unfertilized, unplanted quarter, and two unfertilized quarters with plants. Six weeks after grubs were added, grub densities were highest in fertilized quarters (P < 0.0001), even though the majority of roots were still in the original planted quarters. In another pot experiment, aboveground production was reduced in the presence of grubs (P < 0.03), with greater impacts of grubs on plants in heterogeneous (relative to homogeneous) conditions. In small patches in the field (< 50 cm2), herbivores reduced root mass to a greater extent in fertilized than unfertilized patches (P < 0.01). Finally, in mixed-species field plots (0.50 m2 in area), manipulations of nutrient fertility, heterogeneity, and root herbivory had differential impacts on individual plant species and species groups (i.e., early- vs. late-season dominants). Overall, it appears that grubs are attracted to organic-rich soil patches, and that nutrient heterogeneity may serve as an important template for controlling belowground trophic structure and function.
Key words: Scarabaeidae, rhizivory