PARENT SESSION
Oral Session # 65: Herbivory V: Deer, Geese, and Chemistry.
Presiding: K Bjorndal
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 103.

Linking aboveground and belowground dynamics: Indirect effects of microbe decomposers on plant-herbivore interactions.

Hines, Jessica^*,1, Megonigal, James², Denno, Robert¹, ¹ University of Maryland, College Park, MD, USA² Smithsonian Environmental Research Center, Edgewater, MD, 21037

ABSTRACT- Because plants take up nutrients from the soil and allocate them to the production of leaf tissue, they provide an obvious link between belowground soil nutrient cycling and aboveground interactions between plants and their associated community of insect herbivores. Despite this logical connection, very few studies have examined how plants, and the decomposition of their leaf litter, influence soil microbial processes that in turn alter plant nutrition and the success of aboveground herbivores. To elucidate the indirect effects of leaf litter, as a carbon source for microbes a possible nitrogen sink, on plant-herbivore interactions, we performed a resource subsidy experiment on an Atlantic coast Spartina marsh and measured the consequences for plant quality and aboveground herbivores, namely Prokelisia planthoppers. Treatments were achieved by adding carbon (sucrose), nitrogen (NH4NO3), and leaf litter in a completely randomized factorial field plot experiment for two years. We found that nitrogen addition treatment plots (low C:N) exhibited higher soil nutrient availability, higher plant quality (N content), and higher herbivore abundance. In contrast carbon addition treatment plots (high C:N- designed to enhance the microbial community) showed increased dissolved organic nitrogen, decreased plant quality (plant biomass), and decreased herbivore abundance compared to non-manipulated controls. Thus, leaf litter has the potential to contribute to herbivore dynamics on this salt marsh by indirectly altering the quality of their Spartina host plant by altering microbial nitrogen mineralization. This study emphasizes the importance of linking belowground ecosystem processes such as nutrient cycling and decomposition with aboveground food web interactions.

Key words: belowground, aboveground, ecosystem function, trophic structure