Anthropogenically enhanced atmospheric sulfur (S) and nitrogen (N) deposition has acidified and eutrophied forest ecosystems worldwide. However, both S and N mechanisms have an impact on microbial communities, and the consequences for microbially driven soil functioning differ. We conducted a two-forest stand (Norway spruce and European beech) field experiment involving acidification (sulphuric acid addition) and N (ammonium nitrate) loading and their combination. For four years, we monitored separate responses of soil microbial communities to the treatments and investigated the relations to changes in activity of extracellular enzymes. We observed that acidification selected for acidotolerant and oligotrophic taxa of Acidobacteria and Actinobacteria and decreased bacterial community richness and diversity in both stands in parallel disregarding their original dissimilarities in soil chemistry and microbial communities’ composition. The shifts in bacterial community influenced the stoichiometry and magnitude of enzymatic activity. Bacterial response to experimental N addition was much weaker likely due to historically enhanced N availability. Fungi were not influenced by any treatment during 4-year manipulation. We suggest that in the onset of acidification when fungi remain irresponsive, bacterial reaction might govern the changes in soil enzymatic activity.

中文翻译：

---

在云杉和山毛榉林中，细菌而不是真菌对土壤酸化反应迅速且一致。

人为增加的大气中硫（S）和氮（N）的沉积已酸化和富营养化了全世界的森林生态系统。但是，S和N机理都对微生物群落产生影响，微生物驱动的土壤功能的后果也不同。我们进行了两个森林林分（挪威云杉和欧洲山毛榉）的田间试验，涉及酸化（添加硫酸）和N（硝酸铵）负载及其组合。四年来，我们监测了土壤微生物群落对处理的不同反应，并调查了其与细胞外酶活性变化的关系。我们观察到，酸化用于酸杆菌属和放线菌属的耐酸和寡营养类群，并同时降低了两个林分中细菌群落的丰富度和多样性，而忽略了它们在土壤化学和微生物群落组成方面的原始差异。细菌群落的变化影响了化学计量和酶活性的大小。由于历史上提高了氮的利用率，对实验性氮添加的细菌反应可能要弱得多。在4年的处理过程中，真菌不受任何治疗的影响。我们建议在酸化开始时，真菌仍然没有反应，细菌反应可能会控制土壤酶活性的变化。细菌群落的变化影响了化学计量和酶活性的大小。由于历史上提高了氮的利用率，对实验性氮添加的细菌反应可能要弱得多。在4年的处理过程中，真菌不受任何治疗的影响。我们建议在酸化开始时，真菌仍然没有反应，细菌反应可能会控制土壤酶活性的变化。细菌群落的变化影响了化学计量和酶活性的大小。由于历史上提高了氮的利用率，对实验性氮添加的细菌反应可能要弱得多。在4年的处理过程中，真菌不受任何治疗的影响。我们建议在酸化开始时，真菌仍然没有反应，细菌反应可能会控制土壤酶活性的变化。