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.