HR: 1340h
AN: B53A-0939    [Abstracts]
TI: Aerobic Methane Generation From Plants (AMP)? Yes, Mostly!
AU: * Whiticar, M J
EM: whiticar@uvic.ca
AF: School of Earth and Ocean Sciences, University of Victoria, Rm 118, EHut, P.O. Box 3050, Victoria, BC V8W 2Y2, Canada
AU: Ednie, A C
EM: quebec@uvic.ca
AF: School of Earth and Ocean Sciences, University of Victoria, Rm 118, EHut, P.O. Box 3050, Victoria, BC V8W 2Y2, Canada
AB: In 2006, Keppler et al. (K) published an intriguing and revolutionary idea that aerobic methane is produced in plants (AMP) and released to the atmosphere. Their initial scaling calculations estimated the amount of AMP fluxing from living plants to range from 62-236 Tg/y and 1-7 Tg/y for plant litter. Houweling et al. (2006) (H) refined this flux to ca. 85 Tg/y PIH and 125 Tg/y present day. More recently, Dueck et al. (2007) (D) challenged the claim of AMP from intact plants. Their experiments cited "...No evidence for substantial aerobic methane emission by terrestrial plants..." (max. 0.4 ng/g h^-1). Due to the significance of AMP in understanding present and palaeo-atmospheric budgets (e.g., Whiticar and Schaefer, 2007), we conducted a wide range of experiments to confirm or refute the existence and magnitude of AMP. For explanation, experiments of K were time-series batch samples measured by gas chromatography on purged and ambient samples, whereas D used continuous-flow cuvettes and measured by optical PAS with time series single injections. Our longer-term experiments with corn, wheat, tomato, red cedar, chestnut, moss and lichen (3-97 h, 32 °C) used a plant chamber, flow-through system with a GYRO, an optical spectrometer that enables continuous 1 Hz CH₄ measurements with a precision of ca. 1 ppbv. We conducted over 100 chamber experiments on sterilized and non-sterilized (Cs-137 radiation) samples of: 1) intact living plants (IP), 2) fresh leaves (FL) and 3) dried leaves (DL); under both 1) high and 2) low light conditions (HL, LL), and with 1) ambient CH₄ (AM, ca. 1.92 ppmv) and 2) purged methane (PM, 10 and 96 ppbv) levels. Our results demonstrate that IP-AMs have CH₄ flux rates of 0.74-3.48 ng/g h^-1. In contrast, IP-PMs show intense CH₄ uptake rates of -28.5 to -57.9 ng/g h^-1 (substantially different than K's reported emissions of 12-370 ng/g h^-1 values). Our FL-AM-LL have CH₄ flux rates of 0.36-2.05 ng/g h^-1, whereas FL-AM-HL have significant CH₄ generation of 0.27 to 12.7 ng/g h^-1 (substantially higher than K's max of 3 ng/g h^-1). FL-PM emissions are low (ca. 1 ng/g h^-1). DL CH₄ release is also low ranging from LL of 0.33 to HL of 3.37 ng/g h^-1. Interestingly, our Cs-irradiated FL have increasingly higher CH₄ emission rates with higher radiation dosages. We do not attempt to extrapolate our AMP laboratory experiments to global scales, nor make any physiological, biochemical or mechanistic claims. However at this point our work does indeed confirm that AMP is indeed operative and significant under certain conditions. The magnitude of our small scale, laboratory, AMP emission experiments is consistent with the earlier claims of K and H. We have, to some degree, emulated the experimental designs of both K and D. We remain intrigued by the findings, yet uncertain, if not puzzled, by the process and the discrepancies between groups.
DE: 0490 Trace gases
DE: 1055 Organic and biogenic geochemistry
DE: 1852 Plant uptake
DE: 4930 Greenhouse gases
SC: Biogeosciences [B]
MN: 2007 Fall Meeting