Growing evidence suggests that methane (CH) emissions from tree stems are a potentially significant atmospheric source. However, a comprehensive global assessment of the general pattern and the controlling factors of stem CH emissions is still unavailable. Here, we present a global data-synthesis of 1081 observations from 62 studies to explore the patterns of stem CH emission rate in upland and wetland ecosystems and their controlling factors. The global average stem CH emission rate in uplands was 2.04 ± 0.61 nmol , which was significantly lower than in wetlands (87.08 ± 19.49 nmol ). Angiosperm stem CH emission rates were significantly higher than gymnosperm in both upland and wetland ecosystems. Meanwhile, stem CH emission rate in inland wetlands (101.78 ± 27.44 nmol ) was significantly higher than in coastal wetlands (56.21 ± 19.23 nmol ). In both wetland and upland ecosystems, stem CH emission rate decreased with increasing sampling height, but increased as soil CH emission rate increased. However, the relationship between stem CH emissions and soil CH fluxes was much weaker for uplands, but very strong for wetlands. In wetlands, stem CH emission rate was also regulated by plant properties, as it was negatively correlated with wood specific density, but positively correlated with stem lenticel density. In uplands, tree diameter negatively affected stem CH emission rate. Overall, our results shed light on the magnitude and controlling factors of stem CH emissions in upland and wetland ecosystems and could facilitate their upscaling to ecosystems and identify the role of stem CH emissions in global CH budgets.

中文翻译：

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树干甲烷排放：全球模式和控制因素

越来越多的证据表明，树干排放的甲烷 (CH) 是一个潜在的重要大气源。然而，目前仍无法对植物甲烷排放的总体模式和控制因素进行全面的全球评估。在这里，我们对 62 项研究的 1081 项观测结果进行了全球数据综合，以探索高地和湿地生态系统中茎 CH 排放率的模式及其控制因素。全球旱地平均茎CH排放率为2.04±0.61 nmol，显着低于湿地（87.08±19.49 nmol）。在高地和湿地生态系统中，被子植物茎的CH排放率均显着高于裸子植物。同时，内陆湿地的茎CH排放率（101.78±27.44 nmol）显着高于沿海湿地（56.21±19.23 nmol）。在湿地和高地生态系统中，茎CH排放率随着采样高度的增加而降低，但随着土壤CH排放率的增加而增加。然而，对于高地来说，茎 CH 排放与土壤 CH 通量之间的关系要弱得多，但对于湿地来说则非常强。在湿地中，茎CH排放率也受到植物特性的调节，与木材比重呈负相关，但与茎皮孔密度呈正相关。在高地，树木直径对茎 CH 排放率产生负面影响。总体而言，我们的结果揭示了高地和湿地生态系统中茎甲烷排放的规模和控制因素，可以促进其向生态系统的升级，并确定茎甲烷排放在全球甲烷预算中的作用。