Soil redox conditions exert substantial influence on biogeochemical processes in terrestrial ecosystems. Humid tropical forest soils are often characterized by fluctuating redox, yet how these dynamics affect patterns of organic matter decomposition and associated CO₂ fluxes remains poorly understood. We used a ¹³C-label incubation experiment in a humid tropical forest soil to follow the decomposition of plant litter and soil organic matter (SOM) in response to four redox regimes—static oxic or anoxic, and two oscillating treatments. We used high-resolution mass spectrometry to characterize the relative composition of organic compound classes in the water extractable OM. CO₂ production from litter and SOM showed different responses to redox treatments. While cumulative production of SOM-derived CO₂ was positively correlated with the length of oxic exposure (r = 0.89, n = 20), cumulative ¹³C-litter-derived CO₂ production was not linked to oxygen availability. Litter-derived CO₂ production was highest under static anoxic conditions in the first half of the experiment, and later dropped to the lowest rate amongst the treatments. In anoxic soils, we observed depletion of more oxidized water-extractable OM (especially amino sugar-, carbohydrate-, and protein-like compounds) over the second half of the experiment, which likely served as substrates for anaerobic CO₂ production. Results from two-pool kinetic modeling showed that more frequent anoxic exposure limited decomposition of a slow-cycling C pool, but not a fast-cycling pool. These results suggest that aerobic and anaerobic heterotrophs were equally effective at degrading labile substrates released from fresh plant litter in this humid tropical forest soil, while aerobic decomposers were more effective in breaking down the potentially refractory compounds found in SOM.

土壤氧化还原条件对陆地生态系统的生物地球化学过程具有重大影响。潮湿的热带森林土壤通常以氧化还原酶波动为特征，但是这些动力学如何影响有机物分解和相关的CO ₂通量的模式仍然知之甚少。我们在潮湿的热带森林土壤中使用了¹³ C标签温育实验，以跟踪植物凋落物和土壤有机质（SOM）的分解，以响应四种氧化还原方式-静态氧化或缺氧，以及两种振荡处理。我们使用高分辨率质谱法来表征可水萃取的OM中有机化合物类别的相对组成。一氧化碳₂凋落物和SOM的生产对氧化还原处理表现出不同的反应。虽然SOM衍生的CO _2的累积产生量与氧气暴露的时间呈正相关（r  = 0.89，n  = 20），但¹³ C分解物产生的CO _2的累积产生量与氧气的利用率无关。产自废弃物的CO ₂在实验的前半部分，在静态缺氧条件下产量最高，随后在所有处理中降至最低。在缺氧的土壤中，我们观察到在实验的后半段消耗了更多的氧化水可萃取的OM（尤其是氨基糖，碳水化合物和类似蛋白质的化合物），这很可能是厌氧CO _2的底物生产。两池动力学模型的结果表明，更频繁的缺氧暴露限制了慢循环C池的分解，但不限制快速循环C池的分解。这些结果表明，好氧和厌氧异养菌在降解这种潮湿的热带森林土壤中新鲜植物凋落物中释放的不稳定底物方面同样有效，而好氧分解剂更有效地分解了SOM中潜在的难降解化合物。