Methane (CH₄) emission from tree stems (stem CH₄ emission) is a previously overlooked emission pathway in forested wetlands. Despite growing evidence of its significance to both regional and global CH₄ budgets, the drivers and mechanisms of stem CH₄ emission in wetlands are not fully understood. To clarify the environmental drivers of stem CH₄ emission, we conducted chamber-based flux measurements for mature Alnus japonica and Fraxinus mandshurica trees in a forested wetland in northern Japan over four snow-free seasons, as well as a short-term flooding experiment and an isotopic analysis of stem-emitted and soil porewater CH₄. Stem CH₄ fluxes varied seasonally and annually. The highest flux, exceeding 10,000 µg CH₄ m⁻² h⁻¹, occurred in August 2016 following a record-breaking rainfall. Soil temperature and water-table depth had significant effects on stem CH₄ flux. Artificial flooding remarkably increased stem CH₄ flux more than tenfold within 4 days and elevated fluxes persisted for at least 1 day after the floodwater receded. Stem-emitted CH₄ was depleted in ¹³C by an average of 2–3‰ relative to porewater CH₄, implying isotopic fractionation of CH₄ by diffusion and/or oxidation along its emission pathway. Belowground environmental conditions exhibited considerable control over stem CH₄ emissions in forested wetlands; the biogeochemical and biological mechanisms of this influence should be further explored.

来自树茎的甲烷 (CH ₄ ) 排放（茎 CH ₄排放）是以前在森林湿地中被忽视的排放途径。尽管越来越多的证据表明其对区域和全球 CH ₄预算的重要性，但尚未完全了解湿地干 CH ₄排放的驱动因素和机制。为了阐明茎 CH ₄排放的环境驱动因素，我们对日本北部森林湿地中成熟的桤木和水曲柳树进行了四个无雪季节的基于室内的通量测量，以及短期洪水实验和茎排放和土壤孔隙水 CH ₄的同位素分析. 茎 CH ₄通量季节性和每年变化。最高通量超过 10,000 µg CH ₄ m ^-2  h ^-1，发生在 2016 年 8 月创纪录的降雨之后。土壤温度和地下水位深度对茎干CH ₄通量有显着影响。人工洪水在 4 天内使茎 CH ₄通量显着增加了十倍以上，并且在洪水退去后至少持续了 1 天。相对于孔隙水 CH ₄，杆排放的 CH ₄在¹³ C中消耗了 2–3‰ ，这意味着 CH _{4 的}同位素分馏通过沿其发射路径扩散和/或氧化。地下环境条件对森林湿地的茎 CH ₄排放表现出相当大的控制；应进一步探索这种影响的生物地球化学和生物学机制。