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Effects of elevated atmospheric CO2 and tropospheric O3 on leaf litter production and chemistry in trembling aspen and paper birch communities.

Liu, Lingli*,1, King, John1, Giardina, Chiristian2, 1 School of Forest Resource and Environmental Sciences, Houghton, MI, 499312 USDA Forest Service, North Central Research Station, Houghton, MI, 49931

ABSTRACT- Human activities are increasing the concentrations of CO2 and tropospheric O3 in the atmosphere, and these changes have the potential to alter the quantity and chemical quality of leaf litter inputs to forest soils. In order to evaluate these impacts, we assessed the independent and combined effects of elevated CO2 and elevated O3 on foliar litter production and chemistry of aspen and birch-aspen communities at the Aspen-FACE Project in Rhinelander, WI. Litter was analyzed for total mass and chemistry including carbon (C), nitrogen (N), non-structural carbohydrates, lipids, lignin, cellulose, hemicellulose and carbon-based defensive compounds (soluble phenolics, condensed tannins). We found the concentrations of these chemical compounds in naturally senesced litter were similar in aspen and birch/aspen communities, except for N, the ratio of carbon to nitrogen (C/N) and lipids. Elevated CO2 significantly increased C/N (+8.7 %), lowered litter N concentration (-10.7 %) and had no impacts on the concentrations of soluble sugars, soluble phenolics and condensed tannins. However, elevated CO2 significantly increased litter biomass production (+ 33.3 %), which resulted in significant increase in the fluxes of N, soluble sugars, soluble phenolics and condensed tannins. Elevated O3 significantly increased litter concentration of soluble sugars (+78.1 %), soluble phenolics (+53.1 %) and condensed tannins (+77.2). No significant effects of the CO2 and O3 treatments were observed for the concentration of individual carbon structural carbohydrates (cellulose, hemicellulose, and lignin). However, elevated CO2 significantly increased (+37.4 %) cellulose input to soil, while elevated O3 significantly reduced hemicellulose and lignin inputs to soil (-22.3 and -31.5 %, respectively) by elevated O3. We conclude that small changes in litter chemistry under elevated CO2 and tropospheric O3 will occur, and combined with changes in litter biomass production could significantly alter the inputs of N, soluble sugars, condensed tannins, soluble phenolics, cellulose and lignin to forest soils in the future.

Key words: chemistry, FACE, foliar litter

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