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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Food Webs I
ELEVATED ATMOSPHERIC CO2 ALTERS LEAF LITTER NUTRITIONAL QUALITY: IMPACTS ON THREE TROPHIC LEVELS IN DETRITUS BASED AQUATIC FOOD WEBS.
N.C. Tuchman1,2, B. Swedo1,2, S. Abichandani1, S.T. Rier1,2, and R.G. Wetzel3. 1Department of Biology, Loyola University Chicago, Chicago, IL, USA 60626, 2University of Michigan Biological Station, Pellston, MI, USA 49769, 3Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, NC, USA 27599
Elevated levels of atmospheric CO2 produce nutritionally lower quality leaf litter by enhancing the plant's production of secondary plant defense compounds and lowering foliar nitrogen. Leaf litter of Populus tremuloides was produced in open-top chambers under both ambient (AMB = 360 ppm) and elevated (ELEV = 720 ppm) CO2 levels, and significantly higher C:N, total phenolic compounds, and lignin levels were measured in ELEV litter. Through a series of field and laboratory experiments, growth responses to the altered litter was followed through an aquatic food chain. Biomass and productivity of bacteria and fungi were significantly reduced on ELEV leaf litter after 15d of colonization in a stream. Growth and development rates of mosquito larvae that were fed microbially colonized ELEV leaf litter were significantly reduced. Tissue analyses of the mosquito larvae indicated significantly lower lipid (80%) and carbohydrate (100%) contents per g dry weight in the ELEV mosquitoes. These mosquitoes were then fed to 30 mosquitofish (Gambusia affinis) for 6 weeks and fish growth and “condition” were both significantly reduced. Our results demonstrate a 3-trophic level reduction in secondary production as an indirect function of atmospheric CO2 enrichment with important implications for detritus based aquatic food webs over the next century.
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