Wetland ecosystems hold nearly a third of the global soil carbon pool, but as wetlands rapidly disappear the fate of this stored soil carbon is unclear. The aim of this study was to quantify and then link potential rates of microbial decomposition after vertical drowning of vegetated tidal marshes in coastal Louisiana to known drivers of anaerobic decomposition altered by vegetation loss. Profiles of potential CH₄ and CO₂ production (surface to 60 cm deep) were measured during anaerobic incubations, organic matter chemistry was assessed with infrared spectroscopy, and soil porewater nutrients and redox potentials were measured in the field along a chronosequence of wetland loss. After vertical drowning, pond soils had lower redox potentials, higher pH values, lower soil carbon and nitrogen concentrations, lower lignin: polysaccharide ratios, more NH₄⁺ and PO₄³⁻, and higher rates of potential CO₂ release than vegetated marsh soils. Potential CH₄ production was similar in vegetated marshes and open water ponds, with depth-dependent decreases in CH₄ production as soil carbon concentrations increased. In these anoxic soils, vegetation loss exerts a primary control on decomposition rates because flooding drives sustained increases in porewater nutrient availability (NH₄⁺ and PO₄³, dissolved organic carbon) and decreases in redox potential (from −150 to −500 mV) that lead to higher potential CO₂ fluxes within a few years. Without new carbon inputs following wetland loss, the sustained decomposition in open water ponds may lead to losses of stored soil carbon and could influence global carbon budgets.

中文翻译：

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密西西比河三角洲湿地垂直淹没后的植被损失导致微生物分解加快和土壤碳减少

湿地生态系统拥有全球近三分之一的土壤碳库，但随着湿地的迅速消失，这些储存的土壤碳的命运尚不清楚。本研究的目的是量化路易斯安那州沿海植被潮汐沼泽垂直淹没后微生物分解的潜在速率，然后将其与植被损失改变的已知厌氧分解驱动因素联系起来。在厌氧培养过程中测量了潜在的 CH ₄和 CO ₂产量（表面至 60 厘米深），利用红外光谱评估了有机质化学，并按照湿地损失的时间顺序在现场测量了土壤孔隙水养分和氧化还原电位。垂直淹没后，池塘土壤比植被沼泽土壤具有更低的氧化还原电位、更高的pH值、更低的土壤碳和氮浓度、更低的木质素：多糖比率、更多的NH ₄ ⁺和PO ₄ ³⁻以及更高的潜在CO ₂释放率。植被沼泽和开放水域池塘的潜在 CH ₄产量相似，随着土壤碳浓度的增加， CH ₄产量随深度而下降。在这些缺氧土壤中，植被损失对分解速率起到主要控制作用，因为洪水导致孔隙水养分有效性（NH ₄ ⁺和 PO ₄ ³，溶解有机碳）持续增加，氧化还原电位降低（从 -150 到 -500 mV）这会在几年内产生更高的潜在CO ₂通量。湿地丧失后如果没有新的碳输入，开放水域池塘的持续分解可能会导致储存的土壤碳的损失，并可能影响全球碳预算。