Data from: Drivers of intra-individual spatial variability in methane emissions from tree trunks in upland forest

CH4 emissions from tree trunks in upland forests should be scaled accurately in order to assess the role of tree trunks in the forest CH4 budget. As the chambers used to measure emissions cover only a small part of the tree trunks, it is necessary to understand the intra-individual spatial variability in trunk CH4 emissions. We measured trunk CH4 flux at nine locations per individual on four trees in a cool-temperate upland forest. To appreciate the origin of this variability and the underlying processes, we also measured the potential rate of CH4 production and CH4 concentration at sapwood and characterized wood and bark. Up to 15-fold spatial variation in CH4 fluxes were observed at the individual level. This variability can be highlighted by the variation in the sapwood CH4 concentration which was further explained by the variation in CH4 production rate. The radial CH4 diffusivity calculated from concentration gradients and emissions was not related to the measured characteristics of either wood or bark, raising the question of the diffusion pathway. We emphasized the importance of sampling trunk CH4 flux at multiple locations on the surface of a tree trunk to capture spatial variability, a prerequisite for estimating tree-level CH4 emissions.

为精准评估树干在森林甲烷收支中的作用，需对山地森林树干的甲烷（CH4）排放进行准确尺度转换。由于用于测量排放的气室仅能覆盖树干的极小区域，因此有必要厘清树干甲烷排放的个体内空间变异。本研究在一处寒温带山地森林中，对4棵单株树木分别在9个采样点位开展了树干甲烷通量测定。为探明该变异的来源与潜在过程，我们同时测定了边材（sapwood）的甲烷潜在产生速率与甲烷浓度，并对木材和树皮进行了特征表征。在个体尺度上，观测到的甲烷通量空间变异最高可达15倍。该空间变异可通过边材甲烷浓度的变化得到体现，而边材甲烷浓度的差异又可进一步由甲烷产生速率的变化解释。基于浓度梯度与排放量计算得到的径向甲烷扩散系数与木材或树皮的测定特征均无关联，这引发了关于甲烷扩散路径的疑问。本研究强调，需在树干表面的多个位置开展甲烷通量采样以捕捉空间变异，这是估算单棵树木甲烷排放量的必要前提。