Methane emissions from plants in wetlands are mainly due to internal transport, from the anoxic soil layers where methane is produced, to the atmosphere. This pathway has not yet been clearly demonstrated for upland forest vegetation, where methane can be produced in deep soil layers. We developed a new method to trace methane transfer from the deep soil. We conducted a ¹³CH₄ pulse labelling at 40-cm soil depth and then monitored ¹³CH₄ in the upper horizons, at the soil surface (with or without understorey vegetation) and emitted by tree stems until the total disappearance of the labelled gas. Most of the injected ¹³CH₄ was oxidized in the soil despite high soil water content. The understorey vegetation did not contribute to ¹³CH₄ emission by the soil. We prove that tree stems can emit methane produced in an upland forest soil, even when the said soil is a net methane sink. We conclude that pulse labelling with ¹³CH₄ and tracing by laser-based spectrometry is a promising tool approach to study the transport of methane from production to emission.

湿地植物中的甲烷排放主要是由于内部运输，从产生甲烷的缺氧土壤层到大气。对于山地森林植被而言，该途径尚未被清楚地证明，在该土壤中甲烷可在深层土壤中产生。我们开发了一种追踪深层土壤中甲烷转移的新方法。我们在40 cm的土壤深度上进行了¹³ CH ₄脉冲标记，然后在上层地平线上监测了土壤表面（有或没有地下植被的情况下）的¹³ CH ₄并由树茎发出，直到标记的气体完全消失。大部分已注入的¹³ CH ₄尽管土壤中的水分含量很高，但在土壤中仍被氧化。底层植被没有促进土壤中¹³ CH _4的排放。我们证明，即使所说的土壤是甲烷的净汇，树茎也可以排放出旱地森林土壤中产生的甲烷。我们得出的结论是，用¹³ CH _4进行脉冲标记并通过基于激光的光谱法进行跟踪是研究甲烷从生产到排放的运输的有前途的工具方法。