Bacterial and archaeal communities reflect long-term pH shift induced by ash fertilization in boreal peatland forest soils.

Ash fertilization is a forest management practice used to improve forest growth in boreal peatland forests. It impacts soil chemistry, vegetation and soil organisms, yet little is known about its long-term impacts on soil microbial communities. Here, we focus on the long-term impacts of ash fertilization on the soil microbiome of drained boreal peatland forests in Finland. We hypothesized that the ash-induced changes in soil chemistry have led to long-term changes in soil microbial communities. To study this, we analyzed soil bacterial and archaeal communities from seven drained peatland forest sites in Finland. Each site had an ash fertilized plot (fertilized 8-43 years before sampling) and an unfertilized plot. Soil pH was higher at ash fertilized plots in five out of the seven sites. Pseudomonadota, Bryobacteraceae and Planctomycetaceae were more abundant in samples from the control plots, whereas Actinomycetota were more abundant in samples from the ash‑fertilized plots. According to distance-based redundancy analysis, soil pH was important driver of soil bacterial and archaeal community structure. Site explained a greater proportion of community variation than treatment. Therefore, impacts of wood ash on soil in peatland forest stands should be considered by taking into account their site-specific factors and management history.