The stems of living trees in upland forests might contribute to the global methane (CH₄) source, but the contribution is poorly understood. We investigated CH₄ concentration in the heartwood of living trees in dominant upland forests using field campaign and subsequently evaluated the importance of stem CH₄ emission in the context of the global total. We found that only 0%, 9.8%, and 1.8% of stems of living trees had substantial CH₄ concentration in heartwood of ≥ 10,000 μL L^–1 in the boreal, temperate, and tropical and subtropical upland forests investigated, respectively. CH₄ concentration in heartwood depended mainly upon tree species and subsequently soil moisture. Relationships fitted indicate that CH₄ concentration followed a power function with respect to water content in heartwood, whereas nitrous oxide (N₂O) or carbon dioxide (CO₂) concentration linearly increased with water content in heartwood. Stem CH₄ emission was estimated at approximately 0.2–2 Tg yr^–1 globally, corresponding to less than 0.4% of the global total including all natural plus anthropogenic sources. Water content in heartwood is positively associated with soil water content. Soil water content rarely exceeds 40% v/v in upland forests, indicating stem CH₄ emission occurs mainly in the areas of low-lying upland forests with occasionally moist soils. More attentions should be paid on low-lying upland forests and forested wetlands in future when stem CH₄ emission needs to be estimated in all forests.

Graphic abstract

中文翻译：

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活林心材中甲烷的浓度和旱地森林茎中甲烷的估计排放量

陆地森林中活树的茎可能构成了全球甲烷（CH ₄）的来源，但是人们对此贡献知之甚少。我们使用田间运动调查了占主导地位的旱地森林活树心木中CH _4的浓度，随后评估了在全球总量中茎CH ₄排放的重要性。我们发现，在所调查的北方，温带和热带及亚热带山地森林中，分别只有0％，9.8％和1.8％的活树茎中的≥10,000μLL ^–1的心木中具有大量CH ₄浓度。通道₄心材中的浓度主要取决于树种以及随后的土壤湿度。拟合的关系表明，CH ₄浓度相对于心材含水量呈幂函数关系，而一氧化二氮（N ₂ O）或二氧化碳（CO ₂）浓度随心材含水量线性增加。据估计，全球甲烷CH ₄排放量约为0.2-2 Tg yr ^-1，相当于包括所有自然和人为源在内的全球总量的不到0.4％。心材中的水分与土壤水分呈正相关。旱地森林的土壤水分很少超过40％v / v，表明茎CH ₄排放主要发生在地势低洼，土壤偶尔湿润的地区。当需要估计所有森林中的茎CH ₄排放量时，应在低洼的山地森林和森林湿地上给予更多的关注。

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