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Elevated CO2 and temperature affect C and N concentrations but not accumulation in Pseudotsuga menziesii.
OLSZYK, DAVID1, TINGEY, DAVID1, JOHNSON, MARK1, RYGIEWICZ, PAUL1, 1
ABSTRACT- To determine impacts of climate change on concentrations and accumulation of C and N in trees, we grew Pseudotsuga menziesii (Mirb.) Franco (Douglas-fir) seedlings with ambient or elevated (+180 mol mol-1) CO2, and ambient or elevated (+3.5 C) temperature for four years in outdoor, sun-lit, chambers. We used a wet-winter/dry-summer soil moisture regime and did not add fertilizer. Elevated CO2 decreased leaf % C and % N and increased the C/N ratio. In contrast, elevated temperature increased leaf % C and % N and decreased the C/N ratio. Branch and stem % C and % N were not affected by elevated CO2, while elevated temperature increased branch % C and % N and decreased the C/N ratio in branches and stems. Root %C and % N were not affected by elevated CO2 or temperature. Despite changes in % C and % N in some tissues, the total accumulation of C and N in the plant and relative allocation of C or N to different tree organs were not affected by elevated CO2 or elevated temperature. Therefore, for Pseudotsuga menziesii seedlings growing under natural soil moisture and nutrition conditions, both elevated CO2 and temperature affect aboveground but not belowground tissue quality in terms of C and N concentrations, and may not affect the amount of C or N in the plant.
KEY WORDS: Douglas-fir, climate change, mesocosm