CANCELLED - Mammalian herbivore response to CO2-and O3-mediated changes in plant chemistry

Background/Question/Methods Data produced over the past few decades clearly show that atmospheric carbon dioxide (CO2) and tropospheric ozone (O3) can elicit changes in plant chemistry that alter the behavior and performance of insect herbivores. We know almost nothing, however, about the response of mammalian herbivores to these atmospheric‐mediated changes in plant chemistry. Here, we show that CO2and O3 indirectly affect the growth of a herbivorous rodent, the prairie vole (Microtus ochrogaster), through changes in plant quality. During summer 2007, uncultivated Solidago canadensis and Taraxacum officinale were collected from the aspen‐maple understory of control, elevated CO2, and elevated O3 rings at the Aspen‐FACE research facility in Rhinelander, Wisconsin. These plants were used for chemical analysis (CN, fiber, non‐structural carbohydrates (TNC), and protein‐binding compounds) and in feeding trials to ascertain the growth response of weanling prairie voles to greenhouse gas‐mediated changes in plant chemistry. Fresh test diet was weighed and distributed so that plants from each FACE ring were given exclusively to each of three voles (n= 9 rings x 3 voles = 27). Fresh plants were provided every day in excess. After a two day acclimation period, consumption and body mass were recorded for eight days.

Results/Conclusions   Voles consumed equal amounts of T . officinale and S. canadensis, regardless of fumigation treatment. Fumigation and sex significantly affected vole growth (F2,20, p=<0.05). Compared with controls, females grew 27% and 36% less on CO2‐and O3‐grown diets. Males, however, grew 19% less on CO2 diets, but showed no response to O3. No species by treatment interactions occurred for any plant constituents, suggesting that these plants respond similarly to elev ated CO2 and O3. Elevated CO2 had no effect on CN, whereas elevated O3 elicited a 40% increase (F2,6=, P<0.05). Similarly, TNC increased 47% (F2,6=, P<0.05) and nitrogen content (N, F2,6=, P<0.05) decreased 26% under elevated O3 , but did not change under elevated CO2. Acid detergent fiber (ADF; cellulose, lignin, and ash) content increased 12.6% and 8% under elevated CO2and O3, respectively (F2,6=, P<0.05). ADF/N ratio increased only in plants grown under elevated O3, being 52% higher than controls (F2,6=, P<0.05). Fumigation did not alter the protein‐binding capacity of plants. We show that global atmospheric change has the potential to affect the performance of a mammalian herbivore through changes in plant chemistry. Our work highlights the importance of considering both the direct and indirect effects of global atmospheric change on systems where mammals are key consumers.