Regional variation in Swedish acid sulfate soil microbial communities is influenced by temperature, grain size, and organic matter content

Acid sulfate soils are frequently described as the nastiest soils on Earth and they pose environmental risks associated with their strong acidity and consequential mobilization of toxic metals present in the soils. Within Sweden, acid sulfate soils are extensively studied around the northern Baltic coastline and have now been found to occur along the entire maximum Holocene marine limit. This study investigated 20 actual acid sulfate soils (field pH less than 4.0) collected throughout Sweden that were tested for microbial community composition using 16S rRNA gene amplicons from the oxidized zone, transition zone, and reduced zone. Microbial community compositions were also compared with geochemical analyses from a parallel study. Regional differences of microbial community diversity and composition were identified between samples collected in the north and the south primarily within the oxidized zone, to a lesser degree in the transition zone, while little differences were observed in the reduced zone. In addition, microbial taxa associated with iron and sulfur oxidation and reduction were identified, such as Acidobacteriaceae, Gallionellaceae, and Koribacteraceae that have been previously identified in other acid sulfate soils and acid mine drainage studies. Analysis of the microbial community compositions also identified a north to south regional divide with for instance, differences in relative abundance of Ktedonobacteraceae and Gallionellaceae in the northern and southern oxidized zones, respectively. The study presents an overview of the microbial communities of acid sulfate soils along a 2000 km coastine stretching from a cold boreal zone to a milder hemiboreal zone and suggested that the predominant driver of these community differences was due to soil temperature followed by grain size, and organic matter content.