Floodplain soils are vast reservoirs of organic carbon often attributed to anaerobic conditions that impose metabolic constraints on organic matter degradation. What remains elusive is how such metabolic constraints respond to dynamic flooding and drainage cycles characteristic of floodplain soils. Here we show that microbial depolymerization and respiration of organic compounds, two rate-limiting steps in decomposition, vary spatially and temporally with seasonal flooding of mountainous floodplain soils (Gothic, Colorado, USA). Combining metabolomics and -proteomics, we found a lower abundance of oxidative enzymes during flooding coincided with the accumulation of aromatic, high-molecular weight compounds, particularly in surface soils. In subsurface soils, we found that a lower oxidation state of carbon coincided with a greater abundance of chemically reduced, energetically less favorable low-molecular weight metabolites, irrespective of flooding condition. Our results suggest that seasonal flooding temporarily constrains oxidative depolymerization of larger, potentially plant-derived compounds in surface soils; in contrast, energetic constraints on microbial respiration persist in more reducing subsurface soils regardless of flooding. Our work underscores that the potential vulnerability of these distinct anaerobic carbon storage mechanisms to changing flooding dynamics should be considered, particularly as climate change shifts both the frequency and extent of flooding in floodplains globally.

中文翻译：

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漫滩土壤微生物解聚和有机物氧化的季节控制


洪泛区土壤是巨大的有机碳库，通常归因于厌氧条件对有机物降解施加代谢限制。仍然难以捉摸的是，这种代谢限制如何响应洪泛区土壤的动态洪水和排水循环特征。在这里，我们表明，有机化合物的微生物解聚和呼吸是分解的两个限速步骤，随着山地洪泛区土壤（美国科罗拉多州哥特式）的季节性洪水而在空间和时间上发生变化。结合代谢组学和蛋白质组学，我们发现洪水期间氧化酶丰度较低，同时芳香族高分子量化合物的积累，特别是在表层土壤中。在地下土壤中，我们发现，无论洪水条件如何，碳的较低氧化态与化学还原的、能量上不利的低分子量代谢物的丰度一致。我们的结果表明，季节性洪水暂时限制了表层土壤中较大的、可能源自植物的化合物的氧化解聚；相比之下，无论洪水如何，微生物呼吸的能量限制在更还原的地下土壤中持续存在。我们的工作强调，应考虑这些不同的厌氧碳储存机制对不断变化的洪水动态的潜在脆弱性，特别是当气候变化改变了全球洪泛区洪水的频率和程度时。