Nitrification in forest soils is often associated with increased leaching of nitrate to deeper soil layers with potential impacts on groundwater resources, further enhanced under scenarios of anthropogenic atmospheric nitrogen deposition and predicted weather extremes. We aimed to disentangle the relationships between soil nitrification potential, seepage-mediated nitrate leaching and the vertical translocation of nitrifiers in soils of a temperate mixed beech forest in central Germany before, during and after the severe summer drought 2018. Leaching of nitrate assessed below the litter layer and in 4, 16 and 30 cm soil depth showed high temporal and vertical variation with maxima at 16 and 30 cm during and after the drought period. Maximum of soil potential nitrification activity of 4.4 mg N kg^-1 d^-1 only partially coincided with maximum nitrate leaching of 10.5 kg N ha^-2. Both ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) were subject to translocation by seepage, and AOB decreased at least by half and AOA increased by one to three orders of magnitude in their abundance in seepage with increasing soil depth. On the level of the total bacterial population, an increasing trend with depth was also observed for Cand. Patescibacteria while Bacteroidetes were strongly mobilized from the litter layer but poorly transported further down. Despite stable population densities in soil over time, abundances of AOA, AOB and total bacteria in seepage increased by one order of magnitude after the onset of autumn rewetting. Predicted future higher frequency of drought periods in temperate regions may result in more frequent seepage-mediated seasonal flushes of nitrate and bacteria from forest soils. Moreover, the observed translocation patterns point to taxon-specific differences in the susceptibility to mobilization, suggesting that only selected topsoil derived microbial groups are likely to affect subsoil or groundwater microbial communities and their functional potential.

中文翻译：

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干旱和再湿润事件增强了山毛榉森林土壤中硝酸盐的淋失和渗流介导的微生物的迁移

森林土壤中的硝化作用通常与硝酸盐向深层土壤的淋溶增加有关，对地下水资源有潜在影响，在人为造成的大气氮沉降和极端天气预测的情况下，硝化作用进一步增强。我们旨在弄清德国中部温和的山毛榉森林在2018年夏季严重干旱之前，之中和之后的土壤硝化潜力，渗漏介导的硝酸盐淋失与硝化剂垂直迁移之间的关系。干旱期间及之后，枯枝落叶层，土壤4、16和30 cm土层表现出较高的时间和垂直变化，最大值在16和30 cm。土壤最大硝化活性为4.4 mg N kg ^-1 d^-1仅部分与最大硝酸盐浸出10.5 kg N ha ^-2重合。氨氧化细菌（AOB）和氨氧化古细菌（AOA）都因渗流而易位，随着土壤深度的增加，AOB渗流的丰度至少降低了一半，AOA的丰度提高了1至3个数量级。在总细菌种群的水平上，Cand也观察到随着深度的增加趋势。杆状杆菌，而拟杆菌类则从垫料层中被强烈地动员，但向下运输较差。尽管随着时间的推移土壤中的人口密度稳定，但秋季再湿润后，土壤中AOA，AOB和总细菌的丰度却增加了一个数量级。预计未来温带地区干旱时期的频率会更高，这可能会导致森林土壤中硝酸盐和细菌的渗漏介导的季节性冲洗更加频繁。此外，