Abstract. Anaerobic decomposition of organic carbon (OC) in submerged rice paddies is coupled to the reduction of alternative soil electron acceptors, primarily Fe³⁺. During reductive dissolution of Fe³⁺ from pedogenic oxides, previously adsorbed native soil organic carbon (SOC) could be co-released into solution. Incorporation of crop residues could hence indirectly, i.e. through the stimulation of microbially mediated Fe³⁺ reduction, promote the loss of native SOC via enhanced dissolution and subsequent mineralisation to CO₂ and CH₄. Our aim was to estimate the relevance of such a positive feedback during the degradation of added OC, and to investigate the impact of irrigation management on this mechanism and on priming effects on native SOC decomposition in general. In a six-week pot experiment with rice plants, two Bangladeshi soils with contrasting SOC-to-reducible-Fe (SOC : Fe_ox) ratios were kept under a regime of alternate wetting and drying (AWD) or continuous flooding (CF), and were either amended with maize shoots or not. The δ¹³C signatures of dissolved organic C and emitted CH₄ and CO₂ were used to infer the decomposition of added maize shoots (δ¹³C = −13.0 ‰) versus native SOC (δ¹³C = −25.4 ‰ and −22.7 ‰). Addition of maize residues stimulated the reduction of Fe as well as the dissolution of native SOC, and the latter to a larger extent under CF, especially for the soil with the highest SOC : Fe_ox ratio. Estimated Fe-bound SOC contents denote that stimulated SOC co-release during Fe reduction could explain this positive priming effect on SOC dissolution after the addition of maize. However, priming effects on SOC mineralisation to CO₂ and CH₄ were lower than for SOC dissolution, and were even negative under AWD for one soil. Enhanced reductive dissolution of Fe-bound SOC upon exogenous OC addition therefore does not necessarily lead to stimulated SOC mineralisation. In addition, AWD irrigation was found to decrease abovementioned priming effects.

中文翻译：

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不同灌溉方式下有机碳添加对稻田土壤有机碳分解的影响

摘要。淹水稻田中有机碳（OC）的厌氧分解与其他土壤电子受体（主要是Fe ^3+）的减少有关。在Fe ³⁺从成岩氧化物中还原溶解期间，先前吸附的天然土壤有机碳（SOC）可能会共同释放到溶液中。因此，作物残渣的掺入可以间接地，即通过刺激微生物介导的Fe ³⁺还原，通过增加溶解度和随后矿化为CO ₂和CH ₄来促进天然SOC的损失。。我们的目的是评估添加的OC降解过程中此类正反馈的相关性，并研究灌溉管理对此机制的影响以及对天然SOC分解的引发效应的总体影响。在对水稻植物进行的为期六周的盆栽实验中，将两种具有相反的SOC与可还原Fe（SOC：Fe _ox）比的孟加拉国土壤保持在交替湿润和干燥（AWD）或连续淹水（CF）的状态下，并用或不用玉米芽进行修正。的δ ¹³溶解有机碳和发射CH的Ç签名₄和CO ₂被用于推断加入玉米芽的分解（δ ¹³ C = -13.0‰）相对于天然SOC（δ ¹³C ＝ -25.4‰和-22.7‰）。玉米残留物的添加刺激了铁的还原以及天然SOC的溶解，而后者在CF条件下的溶解程度更大，尤其是对于SOC：Fe _ox比例最高的土壤。估计的铁结合SOC含量表明，在减少铁含量过程中刺激的SOC共释放可以解释这种添加玉米后对SOC溶解的积极启动作用。但是，引发对SOC矿化成CO ₂和CH _4的影响低于SOC的溶出度，甚至在AWD下对一种土壤为负。因此，添加外源OC后，Fe结合SOC的还原还原作用增强，并不一定会导致SOC矿化。另外，发现AWD灌溉降低了上述引发作用。