Bacterial Community Structure of Tundra Soils

Abstract

The arctic region is highly responsive and vulnerable to climate change. Global warming has accelerated glacial retreat in the high Arctic and permafrost thawing. Understanding the structure of arctic soil microbial communities is essential for predicting the response of the permafrost environment to climate change. To determine the composition of the bacterial community and its relationship with soil properties, we investigated the bacterial community structure and properties of surface soil from the moist acidic tussock tundra in Council, Alaska (64°N), and the foreland of the Midtre Lovenbreen glacier in Svalbard (79°N). The bacterial community was analyzed by pyrosequencing of 16S rRNA genes, and the following soil properties were analyzed: soil moisture content (MC), pH, total carbon (TC), total nitrogen (TN), and inorganic nitrogen (NH4+ and NO3-). Bacterial community similarity based on jackknifed unweighted UniFrac distance showed greater similarity across horizontal layers than through the vertical depth in Council, Alaska. Among the soil properties measured, soil pH was the most significant factor correlating with bacterial community in both upper- and lower-layer soils. This study showed that soil depth and pH were the most important soil properties determining bacterial community structure of the subarctic tundra soil in Council, Alaska. The further away from the glacier, the more clay and soil organic carbon contents were observed. In addition, Cyanobacteria, Firmicutes, and Actinobacteria were dominant in soil samples taken close to the glacier, whereas Acidobacteria were abundant further away from the glacier. Diversity indices indicated that the bacterial community changed from a homogeneous ecosystem to a heterogeneous one along the glacier chronosequence/distance from the glacier. Although the bacterial community structure differed on basis of the presence or absence of plants, the soil properties varied depending on soil age. These findings suggest that bacterial succession occurs over time in glacier forelands but on a timescale that is different from that of soil development. The physical and chemical properties of the soil varied significantly along the distance from the Midtre Lovenbreen glacier. The further away from the glacier, the more clay and soil organic carbon contents were observed. In addition, Cyanobacteria, Firmicutes, and Actinobacteria were dominant in soil samples taken close to the glacier, whereas Acidobacteria were abundant further away from the glacier. Diversity indices indicated that the bacterial community changed from a homogeneous ecosystem to a heterogeneous one along the glacier chronosequence/distance from the glacier. Although the bacterial community structure differed on basis of the presence or absence of plants, the soil properties varied depending on soil age. These findings suggest that bacterial succession occurs over time in glacier forelands but on a timescale that is different from that of soil development.