Institute of Forestry and Conservation, John H Daniels Faculty of Architecture Landscape and Design, University of Toronto, 33 Willcocks St. Toronto, ON M5S 3B3, Canada.
Institute of Forestry and Conservation, John H Daniels Faculty of Architecture Landscape and Design, University of Toronto, 33 Willcocks St. Toronto, ON M5S 3B3, Canada.
Sci Total Environ. 2024 Dec 1;954:176503. doi: 10.1016/j.scitotenv.2024.176503. Epub 2024 Sep 27.
Methane (CH₄) and nitrous oxide (N₂O) are critical biogenic greenhouse gases (GHGs) with global warming potentials substantially greater than that of carbon dioxide (CO₂). The exchange of these gases in tropical forests, particularly via foliar processes, remains poorly understood. We quantified foliar CH₄ and N₂O fluxes among tropical tree species and examined their potential association with the leaf economics spectrum (LES) traits. Sampling within Lawachara National Park, Bangladesh, we used in-situ measurements of foliar CH₄ and N₂O fluxes employing off-axis integrated cavity output spectroscopy (CH₄, CO₂ and H₂O) and optical feedback-cavity enhanced absorption spectroscopy (N₂O) analyzers. Leaves were measured under dark, low, and high (0, 100, and 1000 μmol·m·s) light conditions. Surveyed tree species exhibited both net foliar uptake and efflux of CH₄, with a mean flux not different from zero, suggesting negligible net foliar emissions at the stand level. Plant families showed differences in CH₄, but not N₂O fluxes. Consistent efflux was observed for N₂O, with a mean of 0.562 ± 0.060 pmol·m·s. Pioneer species exhibited a higher mean N₂O flux (0.81 ± 0.17 pmol·m·s) compared to late-successional species (0.37 ± 0.05 pmol·m·s). Pioneer species also showed a trend toward a higher mean CH₄ flux (0.24 ± 0.21 nmol·m·s) compared to mid-successional (-0.01 ± 0.26 nmol·m·s) and late-successional species (-0.05 ± 0.28 nmol·m·s). Moreover, among all leaf traits within the leaf economic spectrum, a significant positive relationship was observed between leaf N₂O flux and total leaf nitrogen. Our results suggest that pioneer tree species significantly contribute to net CH₄ and N₂O emissions, potentially counteracting the carbon sequestration benefits in regenerating tropical forests. These findings indicate that accurate GHG budgeting should include direct measurements of foliar CH₄ and N₂O fluxes. Moreover, the results suggest that forest conservation and management strategies that prioritize late successional species will better mitigate GHG emissions.
甲烷（CH₄）和氧化亚氮（N₂O）是重要的生物温室气体（GHGs），其全球变暖潜能远高于二氧化碳（CO₂）。这些气体在热带森林中的交换，特别是通过叶片过程，仍然知之甚少。我们量化了热带树种叶片 CH₄和 N₂O 通量，并研究了它们与叶片经济谱（LES）特征的潜在关联。我们在孟加拉国的拉瓦查拉国家公园内进行采样，使用离轴积分腔输出光谱（CH₄、CO₂ 和 H₂O）和光学反馈腔增强吸收光谱（N₂O）分析仪原位测量叶片 CH₄和 N₂O 通量。在黑暗、低（0、100 和 1000 μmol·m·s）和高光（0、100 和 1000 μmol·m·s）条件下测量叶片。调查的树种表现出 CH₄的净叶片吸收和排放，通量平均值接近零，表明在林分水平上几乎没有净叶片排放。植物科表现出 CH₄通量的差异，但 N₂O 通量没有差异。对于 N₂O，观察到一致的排放，平均值为 0.562 ± 0.060 pmol·m·s。先锋物种的平均 N₂O 通量（0.81 ± 0.17 pmol·m·s）高于晚生物种（0.37 ± 0.05 pmol·m·s）。与中生（-0.01 ± 0.26 nmol·m·s）和晚生（-0.05 ± 0.28 nmol·m·s）物种相比，先锋物种的 CH₄通量（0.24 ± 0.21 nmol·m·s）也呈现出较高的平均值。此外，在叶片经济谱内的所有叶片特征中，叶片 N₂O 通量与总叶片氮之间存在显著的正相关关系。我们的结果表明，先锋树种显著促进了净 CH₄和 N₂O 的排放，可能抵消了热带森林再生过程中的碳固存效益。这些发现表明，准确的温室气体预算应包括叶片 CH₄和 N₂O 通量的直接测量。此外，结果表明，优先考虑晚生物种的森林保护和管理策略将更好地减轻温室气体排放。
