Greenhouse trace gases in deadwood
Deadwood, long recognized as playing an important role in storing carbon and releasing it as CO2 in forest ecosystems, is more recently drawing attention for its potential role in the cycling of other greenhouse trace gases. Across three Northeastern and Central US forests, mean methane (CH4) concentrations in deadwood were 23 times atmospheric levels (43.0 μL L−1 ± 12.3; mean ± SE), indicating a lower bound, mean radial wood surface area flux of ~6 × 10−4 μmol CH4 m−2 s−1. Site, decay class, log diameter, and species were all highly significant predictors of CH4 abundance in deadwood, and diameter and decay class interacted as important controls limiting CH4 concentrations in the smallest and most decayed logs. Nitrous oxide (N2O) concentrations were negatively correlated with CH4 (r2 = −0.20, p < 0.001) and on average ~25 % lower than ambient (276.9 nL L−1 ± 2.9; mean ± SE), indicating net consumption of nitrous oxide. Oxygen (O2) concentrations were uniformly near anaerobic (355.8 μL L−1 ±1.2; mean ± SE), and CO2 was elevated from atmospheric (9336.9 μL L−1 ± 600.6; mean ± SE). Most notably, our observations that CH4 concentrations were highest in the least decayed wood, may suggest that methanogenesis is not fuelled by structural wood decomposition but rather by consumption of more labile nonstructural carbohydrates.
KeywordsClimate change Decomposition Methane Methanogenesis Nitrous oxide Nonstructural carbohydrates Trace gases woody debris
The authors acknowledge the staff of the Yale Myers Forest, and the Tyson Research Center. Shannon Murray, Nora Hawkins, Jacqueline Kulig, and Joanna Parkman assisted with fieldwork at the Yale Myers Forest. This work was supported by National Science Foundation awards granted to KRC and MAB (NSF DGE-1405135), and to AEZ (NSF DEB-1302797). Additional funding was provided by the Yale Institute for Biospheric Studies, the Beck Fund, and the Middlebury Senior Research Project Supplement Award.
KRC, CDO, MAB, XL, CPB, ML, and AEZ planned and designed the research. KRC, CPB, BO, DSM, TWC, and MCD conducted fieldwork. KRC, DSM, and CB analyzed data and designed graphics. KRC, MAB, BO, and BS wrote the manuscript. All authors contributed comments to earlier drafts.
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