Elevated atmospheric CO₂ may have consequences for methane (CH₄) emissions from wetlands, yet the magnitude and direction remain unpredictable, because the associated mechanisms have not been fully investigated. Here, we established an in situ macrocosm experiment to compare the effects of elevated CO₂ (700 ppm) on the CH₄ emissions from two wetlands: an intermittently inundated Calamagrostis angustifolia marsh and a permanently inundated Carex lasiocarpa marsh. The elevated CO₂ increased CH₄ emissions by 27.6–57.6% in the C. angustifolia marsh, compared to a reduction of 18.7–23.5% in the C. lasiocarpa marsh. The CO₂-induced increase in CH₄ emissions from the C. angustifolia marsh was paralleled with (1) increased dissolved organic carbon (DOC) released from plant photosynthesis and (2) reduced (rate of) CH₄ oxidation due to a putative shift in methanotrophic community composition. In contrast, the CO₂-induced decrease in CH₄ emissions from the C. lasiocarpa marsh was associated with the increases in soil redox potential and pmoA gene abundance. We synthesized data from worldwide wetland ecosystems, and found that the responses of CH₄ emissions to elevated CO₂ was determined by the wetland water table levels and associated plant oxygen secretion capacity. In conditions with elevated CO₂, plants with a high oxygen secretion capacity suppress CH₄ emissions while plants with low oxygen secretion capacity stimulate CH₄ emissions; both effects are mediated via a feedback loop involving shifts in activities of methanogens and methanotrophs.

大气 CO ₂升高可能会对湿地的甲烷 (CH ₄ ) 排放产生影响，但其大小和方向仍然不可预测，因为相关机制尚未得到充分研究。在这里，我们建立了一个原位宏观实验来比较升高的 CO ₂ (700 ppm) 对来自两个湿地的 CH ₄排放的影响：间歇性淹没的Calamagrostis angustifolia沼泽和永久淹没的Carex lasiocarpa沼泽。升高的 CO ₂使C. angustifolia 的CH ₄排放量增加了 27.6–57.6%沼泽，相比之下C. lasiocarpa沼泽减少了 18.7-23.5% 。CO ₂诱导的C. angustifolia沼泽的CH ₄排放增加与 (1) 植物光合作用释放的溶解有机碳 (DOC) 增加和 (2)由于假定的转变而降低的 CH ₄氧化（速率）平行在甲烷营养群落组成中。相比之下，C. lasiocarpa沼泽中CO ₂诱导的CH ₄排放减少与土壤氧化还原电位和pmoA基因丰度的增加有关。我们综合了全球湿地生态系统的数据，发现 CH 的响应₄排放到升高的 CO ₂是由湿地地下水位水平和相关的植物氧气分泌能力决定的。在CO ₂升高的条件下，高氧分泌能力的植物抑制CH ₄排放，而低氧分泌能力的植物刺激CH ₄排放；这两种效应都是通过一个反馈回路介导的，该回路涉及产甲烷菌和甲烷氧化菌活动的变化。