Redox gradients structure microbial communities in polygonized Arctic wet tundra soils

This study investigated how microbial community structure and diversity varied with depth and microtopography in ice wedge polygons of wet tundra of the Arctic Coastal Plain in northern Alaska, and what soil variables explain these spatial patterns. We observed strong changes in community structure and diversity with depth, and more subtle changes between areas of high and low microtopography, with the largest differences apparent near the soil surface. These patterns arose primarily from redox gradients (measured using the ratio of reduced Fe to total Fe in acid extracts as a proxy): conditions grew more reducing with depth and were most oxidized in shallow regions of polygon rims. Organic matter and pH also changed with depth and microtopography, but were less effective predictors of the microbial community structure and relative abundance of specific taxa. Of all other measured variables, lactic acid concentration was the best, in combination with redox, for describing the microbial community. We conclude that redox conditions are the dominant force in shaping microbial communities in this landscape. Oxygen and other electron acceptors allowed the greatest diversity of microbes to flourish: in their absence the community was reduced to a simpler core of anaerobes, dominated by fermenters.