The relevance of soil greenhouse gas (GHG) fluxes from temperate floodplain forests has yet remained elusive. We studied the soil methane (CH₄), nitrous oxide (N₂O) and carbon dioxide (CO₂) dynamics at three forest sites along a flooding gradient in the Danube National Park (Austria) to estimate annual GHG budgets and to assess if and how seasonal flooding affects individual GHG fluxes. Soil surface GHG fluxes were determined along with GHG concentrations in soil air and pore-water at a non-flooded (NF), an infrequently-flooded (IF), and a frequently-flooded (FF) site. Both study years were characterized by dry summers, and only the FF site was flooded during the study period. Soils at all sites were annual CH₄ sinks (NF: − 4.50 ± 0.85, IF: − 2.54 ± 0.57, FF: − 0.67 ± 1.06 kg CH₄-C ha⁻¹ year⁻¹) and the sink strength correlated positively with soil moisture. Pulse-like CH₄ emissions were not observed during or after flooding. Soil N₂O fluxes showed large temporal and spatial variations, without any significant differences between sites (average NF: 6.5 ± 7.1, IF: 10.4 ± 14.3, FF: 9.4 ± 10.5 µg N₂O-N m⁻² h⁻¹). Pulse N₂O emissions (up to ~ 80 µg N₂O-N m⁻² h⁻¹) occurred during freeze/thaw events, but not during or after flooding. Mean annual soil CO₂ effluxes at NF and IF were 9.4 ± 1.1 and 9.4 ± 2.1 t C ha⁻¹ year⁻¹, respectively. Soil CO₂ efflux was significantly higher at the FF site (18.54 ± 6.21 t C ha⁻¹ year⁻¹). High soil air CO₂ concentrations (> 10%) in aerated deeper soil layers indicated a substantial contribution of the usually waterlogged sub-soils to the summertime soil CO₂ efflux at the FF site. Overall, our results suggest that the studied temperate floodplain forest soils do not absorb/emit substantially more CH₄ and N₂O than soils of comparable upland forests, whereas low groundwater level can lead to periodically enhanced CO₂ emissions from normally waterlogged soil layers.

来自温带洪泛区森林的土壤温室气体 (GHG) 通量的相关性仍然难以捉摸。我们研究了多瑙河国家公园（奥地利）沿洪水梯度的三个森林地点的土壤甲烷 (CH ₄ )、一氧化二氮 (N ₂ O) 和二氧化碳 (CO ₂ ) 动态，以估计年度温室气体预算并评估是否以及季节性洪水如何影响个人温室气体通量。在非淹水 (NF)、不经常淹水 (IF) 和经常淹水 (FF) 地点，土壤表面 GHG 通量与土壤空气和孔隙水中的温室气体浓度一起测定。两个研究年份的特点都是夏季干燥，在研究期间只有 FF 站点被洪水淹没。所有地点的土壤均为年度 CH ₄汇（NF：- 4.50 ± 0.85，IF：- 2.54 ± 0.57，FF：- 0.67 ± 1.06 kg CH ₄ -C ha ^-1 年^-1）和汇强度与土壤水分正相关。在洪水期间或洪水之后未观察到脉冲状 CH _4排放。土壤 N ₂ O 通量表现出较大的时间和空间变化，地点之间没有任何显着差异（平均 NF：6.5 ± 7.1，IF：10.4 ± 14.3，FF：9.4 ± 10.5 µg N ₂ O-N m ^-2  h ^-1）。脉冲 N ₂ O 排放（高达 ~ 80 µg N ₂ O-N m ^-2  h ^-1) 发生在冻融事件期间，但不会在洪水期间或之后发生。NF 和 IF 的年平均土壤 CO _{2流出量分别为 9.4 ± 1.1 和 9.4 ± 2.1 t C ha} ^-1  year ^-1。FF 站点的土壤CO _{2流出量显着更高（18.54 ± 6.21 t C ha} ^-1 年^-1）。通气较深土壤层中的高土壤空气CO ₂浓度（> 10％）表明通常浸水的底土对FF站点夏季土壤CO _{2外流的重要贡献。}总体而言，我们的结果表明，所研究的温带洪泛区森林土壤不会吸收/释放更多的 CH ₄和 N ₂O 比可比较的高地森林的土壤，而低地下水位会导致从通常淹水的土壤层周期性地增加 CO ₂排放。