Trees in wetlands emit a significant amount of methane (CH₄) into the atmosphere which is produced in the soil where anaerobic conditions prevail. However, only very few studies have considered the role of trees in the CH₄ budget of mangrove forests. How tree CH₄ emissions ($F_{{\mathrm{CH}}_4}$) vary between and within individuals, and how these emissions vary with the day/night alternation and the tidal cycle, have not yet been elucidated. We measured $F_{{\mathrm{CH}}_4}$ from buttress roots and stems on individuals of Bruguiera gymnorrhiza of different sizes. We also measured $F_{{\mathrm{CH}}_4}$ from trees and sediments over a 24-h cycle. Higher $F_{{\mathrm{CH}}_4}$ was measured on the buttress roots than on the stems, with a decreasing trend with height along the stems on a majority of trees. $F_{{\mathrm{CH}}_4}$ exhibited large variations over a 24-h cycle which were observed for the first time in this study. $F_{{\mathrm{CH}}_4}$ from sediment was twice higher at low tide compared to just before or after the flood period. $F_{{\mathrm{CH}}_4}$ from non-submerged stem positions at high tide was four times higher during the day than during the night. On buttress roots and on stem portion which were submerged, high $F_{{\mathrm{CH}}_4}$ were measured at the beginning of the ebb tide even at night. A better understanding of $F_{{\mathrm{CH}}_4}$ variability from mangrove trees and its controls, at different time scales and along spatial gradients is needed for accurate estimation of CH₄ budgets of mangrove forests.

中文翻译：

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亚热带红树林木榄树茎和板根甲烷排放的变化

湿地中的树木向大气中排放大量甲烷 (CH ₄ )，这些甲烷是在缺氧条件下的土壤中产生的。然而，只有极少数研究考虑了树木在红树林CH ₄预算中的作用。树木如何排放CH _{4 (}$F_{{\mathrm{CH}}_4}$）在个体之间和个体内部存在差异，以及这些排放如何随着昼夜交替和潮汐周期而变化，尚未阐明。我们测量了$F_{{\mathrm{CH}}_4}$来自不同大小的木榄个体的板状根和茎。我们还测量了$F_{{\mathrm{CH}}_4}$来自树木和沉积物 24 小时循环。更高$F_{{\mathrm{CH}}_4}$在板根上测量的高度高于在茎上测量的高度，大多数树木沿茎的高度呈下降趋势。$F_{{\mathrm{CH}}_4}$在 24 小时周期内表现出巨大的变化，这是本研究中首次观察到的。$F_{{\mathrm{CH}}_4}$与洪水期之前或之后相比，低潮时来自沉积物的水量高出两倍。$F_{{\mathrm{CH}}_4}$高潮时从非浸没的茎位置发出的水量白天比夜间高四倍。板根和淹没的茎部分，高$F_{{\mathrm{CH}}_4}$即使是在晚上，也是在退潮开始时进行测量的。更好地理解$F_{{\mathrm{CH}}_4}$_{为了准确估计红树林的 CH 4}预算，需要红树林及其控制在不同时间尺度和空间梯度上的变异性。