Common assumptions about how vegetation affects wetland methane (CH₄) flux include acting as conduits for CH₄ release, providing carbon substrates for growth and activity of methanogenic organisms, and supplying oxygen to support CH₄ oxidation. However, these effects may change through time, especially in seasonal wetlands that experience drying and rewetting, or change across space, dependent on proximity to vegetation. In a mesocosm study, we assessed the impacts of Typha on CH₄ flux using clear flux chamber measurements directly over Typha plants (“whole‐plant”), adjacent to Typha plants (where roots were present but no stems; “plant‐adjacent”), and plant‐free soils (“control”). During the establishment phase of the study (first 30 days), the whole‐plant treatment had ~5 times higher CH₄ flux rates (51.78 ± 8.16 mg‐C m⁻²day⁻¹) than plant‐adjacent or control treatments, which was primarily due to plant‐mediated transport, with little contribution from diffusive‐only flux. However, porewater CH₄ concentrations were relatively low directly below whole‐plant and in neighboring plant‐adjacent treatments, while controls accumulated a highly concentrated reservoir of porewater CH₄. When the water table was drawn down to simulate seasonal drying, reserve porewater CH₄ from control soil was released as a pulse, equaling the earlier higher CH₄ emissions from whole‐plants. Plant‐adjacent treatments, which had neither plant‐mediated CH₄ transport nor a concentrated reservoir of porewater CH₄, had low CH₄ flux throughout the study. Our findings indicate that in seasonal wetlands, vegetation affects the timing and location of CH₄ emissions. These results have important mechanistic and methodological implications for understanding the role of vegetation on wetland CH₄ flux.

中文翻译：

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植被影响湿地甲烷排放的时间和位置

关于植被如何影响湿地甲烷（CH ₄）通量的常见假设包括充当CH ₄释放的管道，为产甲烷生物的生长和活性提供碳底物以及提供氧气以支持CH ₄氧化。但是，这些影响可能会随时间变化，尤其是在经历干燥和重新润湿的季节性湿地中，或者在整个空间中变化，这取决于与植被的接近程度。在中观研究中，我们直接在邻近香蒲的香蒲植物（“整个植物”）上使用清晰的通量室测量值评估了香蒲对CH ₄通量的影响。植物（存在根但没有茎的植物；“邻近植物”）和无植物土壤（“对照”）。在研究的建立阶段（前30天），全植物处理的CH ₄通量率（51.78±8.16 mg-C m ^-2天^-1）是植物邻近或对照处理的约5倍。主要是由于植物介导的运输，仅扩散通量贡献很小。但是，在整株植物的正下方和邻近植物的相邻处理中，孔隙水CH _4的浓度相对较低，而对照则积累了高度浓缩的孔隙水CH ₄储集层。下拉水位以模拟季节性干燥时，保留孔隙水CH ₄对照土壤中的脉冲状释放出来，等于整个植物中较高的CH ₄排放量。在整个研究过程中，既没有植物介导的CH ₄转运也没有浓缩的孔隙水CH _4的植物相邻处理的CH ₄通量较低。我们的发现表明，在季节性湿地中，植被会影响CH ₄排放的时间和位置。这些结果对于理解植被对湿地CH ₄通量的作用具有重要的机理和方法学意义。