Grantee Research Project Results
Consequences of Elevated CO2 for a Sensitive Wetland Food WebEPA Grant Number: F5F21616
Title: Consequences of Elevated CO2 for a Sensitive Wetland Food Web
Investigators: Hines, Jessica
Institution: University of Maryland - College Park
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2005 through August 31, 2008
Project Amount: $108,631
RFA: STAR Graduate Fellowships (2005) RFA Text | Recipients Lists
Research Category: Academic Fellowships
Although predicted global changes in atmospheric CO2 levels have the potential to alter the composition of plant communities and their interactions with other trophic levels, there has been very little investigation into the impact of elevated CO2 levels on naturally complex community assemblages. Relatively short-term laboratory experiments on single herbivore species account for the majority of the reports on CO2-plant-insect interactions published in the last few decades. Therefore, in the context of altered food web dynamics, I propose to answer the following questions on a Chesapeake Bay wetland marsh habitat:
- Do changes in the physiology and/or elemental composition of host plants alter the stoichiometry (C:N) of herbivores, and predators?
- Does exposure of C3 and C4 plant communities to elevated CO2 alter herbivore and predator performance?
- Does predator feeding behavior change in response to abundance, quality, and behavior of prey (leaf chewers and phloem feeders) feeding on C3 and C4 plants under elevated CO2 conditions?
The existing elevated-CO2 chambers at Smithsonian Environmental Research Center are ideal for experimental fieldwork. Because the chambers were established in 1987 they have provided the opportunity for long-term arthropod population growth and/or decline. There are three plant treatments enclosed in the chambers (Scirpus olneyi, a C3 sedge; Spartina patens, a C4 grass, and a mixed culture including both Scirpus and Spartina) crossed with three CO2 treatments (twice ambient chamber: 690 ppmv, ambient chamber: 345ppmv, and a companion open plot without a chamber). Each CO2 treatment is replicated five times for a total of 45 experimental units. These open-top chambers (0.8 m diameter, 1.5 m tall) are used to elevate the CO2 content of the atmosphere around the leaves of the vegetation while allowing for colonization and escape of herbivorous insects and their predators. I will track changes in host plant growth (biomass) and quality (%N, C:N) throughout the growing season. Arthropods will be sampled in the open-topped CO2 chambers using a modified D-vac vacuum sampler. I will measure arthropod species abundance, feeding guild, stoichiometry (C:N), and stable isotopic signature (C and N). This will provide both an index of the long-term effects of elevated CO2 on arthropod community structure, and the distribution of nutrients (C:N) between trophic levels and competing species.
I predict that herbivore and predator performance will be determined by food quality and feeding guild. Therefore, I predict that under elevated CO2 conditions predators will perform best when feeding on leaf-chewing herbivore prey because leaf-chewers are expected to maintain homeostasis (body size and C:N) by compensatory feeding, but have increased development time. Phloem-feeders will show the strongest positive response to elevated CO2, whereby they will escape predation because of decreased development time, and decreased nutritional quality (higher C:N). The results of these experiments will be integrated into a clear picture of elevated CO2 effects on herbivores with extended effects at higher trophic levels and food web structure.