PARENT SESSION
Poster Session #49: Elevated CO2 II.
Thursday, August 8. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC
15
Influence of elevated CO2 on carbon storage, water use, and gas exchange of Eastern cottonwoods.
BARRON-GAFFORD, GREG*,1, GRIEVE, KATIE1, PAIGE, TERENCE1, PATTERSON, LANE1, MURTHY, RAMESH1,2, GRIFFIN, KEVIN2, 1 Biosphere 2 Center, Oracle, AZ2 Lamont-Doherty Earth Obervatory, Palisades, NY
ABSTRACT- Eastern Cottonwood (Populus deltoides Bartr.) stands were established in 1998 and grown under ambient (400 ppm), twice-ambient (800 ppm), and three-times-ambient (1200 ppm) atmospheric CO2 concentrations from 2000 until present within the environmentally controlled greenhouse system of the Biosphere 2 Center. The stands were coppiced annually, allowing for new growth the following year. Average tree growth rates, heights and diameters, and measures of aboveground biomass increased each consecutive year. Preliminary results indicate that midday water potentials increased (less negative) with increasing CO2 concentration, implying a greater water use efficiency under elevated CO2. Average 2001 growing season Amax values for the 400, 800, and 1200 ppm stands were 19.2, 26.5, and 32.7 mmolm-2s-1, respectively. Interestingly, this increase in maximum photosynthetic rates with increasing CO2 did not result in a proportional increase in plant biomass during the 2001 growing season. After the 2001 growing season the 400, 800, and 1200 ppm stands yielded approximately 14169, 14671, and 13358 kg ha-1, respectively, of stem and branch biomass. This drop in aboveground C storage within 1200 ppm stand in 2001 does not appear to have been the result of a shift to belowground root production or decreased available soil nitrogen. Monthly measures of soil nitrate levels illustrate no significant difference between the stands, regardless of atmospheric CO2 level. Reasons for this anomaly are being investigated this year.
KEY WORDS: elevated carbon dioxide, eastern cottonwood, carbon storage, forest growth