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ASSESSING THE EFFECTS OF ELEVATED ATMOSP;HERIC CO2 AND TEMPERATURE ON FINE ROOT PRODUCTION AND MORTALITY IN FORESTED SYSTEMS
Citation:
Johnson, M G., P T. Rygiewicz, D T. Tingey, AND D L. Phillips. ASSESSING THE EFFECTS OF ELEVATED ATMOSP;HERIC CO2 AND TEMPERATURE ON FINE ROOT PRODUCTION AND MORTALITY IN FORESTED SYSTEMS. Presented at The Science of Changing Climates: Impact on Agriculture, Forestry and Wetland, University of Alberta, Canada, July 20-23, 2004.
Description:
Little is known about the effects of global climate change on the production and mortality of fine roots. To better understand these processes we have conducted a number of studies to investigate the factors that influence the production and mortality of fine roots in coniferous forest species in the Pacific Northwest. A survey of our findings will be presented. The primary focus of this presentation, however, will be the results of a 4-year study that we conducted to determine the effects of elevated CO2 and temperature on Douglas fir fine ( 2 mm in diameter) roots. This study was conducted in sun-lit controlled-environment chambers located in Corvallis, Oregon, USA. The experiment had a 2 by 2-factorial design [2 levels of CO2 (ambient CO2 and ambient CO2 + 200 mol/mol) and 2 levels of air temperature (ambient temp. and ambient temp. + 4 C)] with 3 replicates. Four horizontal clear plastic minirhizotron tubes were installed in the soil compartment of each chamber. Seedlings were planted in a reconstructed native forest soil that was irrigated to replicate the wet-winter and dry-summer moisture regimen of the Pacific Northwest. Root images were recorded on video tape every four weeks using a minirhizotron camera system. Fine root lengths and diameters were measured from the video tapes using an interactive PC-based software program. More than 138,000 root images were collected and used in this analysis. Minirhizotron data were converted to area biomass density (g/m2) using specific root length (m/g) obtained from roots collected in soil cores The majority of roots observed were very fine ( 1 mm in diameter). Elevated temperature increased the production of very fine roots in the first year at both CO2 levels. Overall, elevated temperature increased the mortality of very fine roots. Elevated CO2 had no significant effect on the production and mortality of the very fine roots. More roots in the 1-2 mm diameter size class were observed in the elevated CO2 treatment. Limitations of soil nitrogen availability likely influenced the response of Douglas fir seedlings to elevated CO2 and temperature in this experiment.