Rapid bark-mediated tree stem methane transport occurs independently of the transpiration stream in Melaleuca quinquenervia

This electronic data available here was used to write the manuscript titled: Rapid bark-mediated tree stem methane transport occurs independently of the transpiration stream in Melaleuca quinquenervia, which was accepted in New Phytologist (27/10/2023).

A summary of the research findings in this publication are:
• Tree stem methane emissions are important components of lowland forest methane budgets. The potential for species-specific behaviour among co-occurring lowland trees with contrasting bark characteristics has not been investigated.

• We compare bark-mediated methane transport in two common lowland species of contrasting bark characteristics (Melaleuca quinquenervia featuring spongy/layered bark with longitudinally-continuous airspaces and Casuarina glauca featuring hard/dense common bark) through several manipulative experiments.

• Firstly, the progressive cutting through M. quinquenervia bark layers caused exponential increases in methane fluxes (~3 orders of magnitude), however sapwood-only fluxes were lower, suggesting that upward/axial methane transport occurs between bark layers. Secondly, concentrated methane pulse injections into exposed M. quinquenervia bark, revealed rapid axial methane transport rates (1.42 mm/s), which were further supported through lab-simulated experiments (1.41 mm/s). Lab-simulated radial CH4 diffusion rates (through bark) were ~20-times slower. Finally, girdling M. quinquenervia stems caused a near-instantaneous decrease in methane flux immediately above the cut. In contrast, girdling C. glauca displayed persistent, though diminished, methane fluxes.

• Overall, the experiments revealed evidence for rapid ‘between-bark’ methane transport independent from the transpiration stream in M. quinquenervia, which facilitates diffusive axial transport from the rhizosphere and/or sapwood sources. This contrasts with the slower, radial ‘through-bark’ diffusive-dominated gas transportation in C. glauca.

本处可获取的电子数据被用于撰写题为《Melaleuca quinquenervia 中快速树干介导的甲烷运输独立于蒸腾流》的论文，该论文已由《New Phytologist》杂志接受（2023年10月27日）。该出版物中的研究结论概述如下：
• 树干甲烷排放是低地森林甲烷预算的重要组成部分。尚未对共存于低地森林中具有不同树皮特征的树木的物种特异性行为进行研究。
• 我们通过一系列操控实验，比较了两种具有不同树皮特征的常见低地树种（Melaleuca quinquenervia 具有海绵/层状树皮和纵向连续的空气空间，Casuarina glauca 具有坚硬/致密的普通树皮）的树皮介导的甲烷运输。
• 首先，对 M. quinquenervia 树皮层的渐进性切割导致甲烷通量呈指数级增加（约3个数量级），然而仅含木质部的通量较低，这表明向上/轴向的甲烷运输发生在树皮层之间。其次，对暴露的 M. quinquenervia 树皮进行集中甲烷脉冲注入，揭示了快速的轴向甲烷运输速率（1.42 mm/s），这一结果通过实验室模拟实验得到了进一步证实（1.41 mm/s）。实验室模拟的通过树皮的径向 CH4 扩散速率慢约20倍。最后，环绕 M. quinquenervia 树干导致切割上方甲烷通量几乎立即下降。相比之下，环绕 C. glauca 的甲烷通量持续存在，尽管有所减弱。
• 总体而言，实验揭示了 Melaleuca quinquenervia 中独立于蒸腾流的快速“树皮之间”甲烷运输的证据，这促进了来自根围和/或木质部来源的扩散性轴向运输。这与 C. glauca 中较慢的、以扩散为主导的径向“通过树皮”的气体运输形成对比。