Flooding and climate warming lead to the increase of low‐molecular‐weight organic acid (LMWOA) inputs to soil. However, it is unclear what the effects of flooding and climate warming on soil nitrogen fraction transformation under LMWOA input are. Fluvisol was collected in the riparian zone of the Three Gorges Reservoir to conduct an incubation experiment with the treatments of three LMWOAs at five contents, two hydrological environments and two temperatures. Compared with LMWOA input of 0 mg kg−1, the soil nitrogen in ion exchangeable fraction (IEF‐N), strong oxidant extractable fraction (SOEF‐N) and non‐transformable nitrogen (NTF‐N) were increased by 35.77, 54.71 and 25.49 mg kg−1, respectively, under LMWOA input of 40 mmol kg−1. Soil nitrogen in the weak acid extractable fraction (WAEF‐N) was decreased by 117.41 mg kg−1. Microbial biomass nitrogen (MBN) was increased by 25.29 mg kg−1, and calcium carbonate (CaCO3) was decreased by 8.03 g kg−1. The contents of IEF‐N, NTF‐N and amorphous iron oxides were higher under the flooding environment than under the drying environment. In contrast, opposite results were observed for soil nitrogen in the strong alkali extractable fraction (SAEF‐N), SOEF‐N and MBN. IEF‐N and NTF‐N contents were higher at 20°C than at 30°C, and the contents of SOEF‐N and MBN were higher at 30°C than at 20°C. WAEF‐N was dissolved by LMWOA through CaCO3 dissolution. The dissolved WAEF‐N was partly transformed into SOEF‐N and NTF‐N by microbial assimilation and humification. Flooding desorbed SAEF‐N through the crystalline transformation of iron oxides. Flooding inhibited the transformation of IEF‐N to SOEF‐N and promoted the formation of NTF‐N, while warming did the opposite. The results provide a perspective of the bound state between soil and nitrogen for understanding the soil nitrogen cycling and help to assess the impacts of climate warming and flooding on soil nitrogen loss from soil to the surrounding water.

中文翻译：

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低分子量有机酸输入下洪水和变暖对土壤氮组分转化的影响

洪水和气候变暖导致土壤中低分子量有机酸（LMWOA）的输入量增加。然而，目前尚不清楚洪水和气候变暖对LMWOA输入下土壤氮组分转化的影响。在三峡水库河岸带采集氟维土，对三种LMWOA在5种含量、2种水文环境、2种温度下的处理进行孵化实验。与 0 mg kg 输入的 LMWOA 相比−1离子交换组分（IEF-N）、强氧化剂可萃取组分（SOEF-N）和不可转化氮（NTF-N）中的土壤氮分别增加了35.77、54.71和25.49 mg·kg−1，分别在 40 mmol kg 的 LMWOA 输入下−1。弱酸可提取部分（WAEF-N）中的土壤氮减少了117.41 mg kg−1。微生物量氮（MBN）增加25.29 mg·kg−1，和碳酸钙（CaCO33) 减少了 8.03 g kg−1。浸水环境下IEF-N、NTF-N和非晶态氧化铁的含量高于干燥环境。相反，强碱可提取部分（SAEF-N）、SOEF-N 和 MBN 中的土壤氮却观察到了相反的结果。 20℃时IEF-N和NTF-N的含量高于30℃，SOEF-N和MBN的含量在30℃时高于20℃。 WAEF-N 通过 CaCO 被 LMWOA 溶解3溶解。溶解的WAEF-N通过微生物同化和腐殖化部分转化为SOEF-N和NTF-N。驱替通过氧化铁的结晶转变解吸SAEF-N。洪水抑制了IEF-N向SOEF-N的转化并促进了NTF-N的形成，而变暖则相反。研究结果为了解土壤氮循环提供了土壤和氮之间结合态的视角，并有助于评估气候变暖和洪水对土壤氮从土壤到周围水体流失的影响。