Methane Concentration in the Heartwood of Living Trees and Estimated Methane Emission on Stems in Upland Forests
2021
Wang, Zhi-Ping | Li, Huan-Long | Wu, Hong-Hui | Han, Shi-Jie | Huang, Jian-Hui | Zhang, Xi-Mei | Han, Xing-Guo
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.
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