Study of soil acidification and nitrogen loading effect on soil microbial communities, Načetín experimental site. Nacetin 2017

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.