Study on Prokaryotic Community Structure in Moist Acidic Tundra Soil in Council, Alaska

Abstract

The Arctic has gained much scientific attention because global warming is predicted to be greatest and most rapid at high latitudes. A point that should yield scientific attention might be concerned about the loss of soil organic matter (SOM), as it contributes to the positive feedback of global warming. Because a warmer climate will cause carbon stored in the soil to be released into the atmosphere via microbial decomposition. With increasing scientific attention on permafrost environments impacted by global warming, many scientists have focused on the global carbon cycle in Arctic soils observing microbial life. However, knowledge on microbial community and diversity in Arctic soil yet very lacking. Thus, this study investigated prokaryotic community structure, diversity and ecological functions in moist acidic tundra soil of Alaska through the next generation sequencing (NGS) with bioinformatics processing. Moreover, this study investigated the relationship between microbial communities and soil properties. In chapter1, a general introduction with background information on Arctic environment and on the necessity of research objectives to explain further chapters is given. In chapter 2, bacterial community structure and its relationship to soil properties in moist acidic tundra soil are described. Although various plants covered the top soil and some vegetation formed a colony, the bacterial communities were not related with vegetation types. Rather, the bacterial community could be markedly differentiated by soil depth and soil pH. The vertical structure of soil profile from active layer to permafrost was observed to be more specific. All soil properties changed along soil depth, and the soil cores were divided by the decomposition status of soil organic matter (SOM). When I observed the shift of bacterial community from active layer to permafrost, active layer could be divided into Oi, Oe and OA horizons, and permafrost was classified as A horizon. Some bacterial groups abruptly changed near the boundary separating the horizons. Briefly, Acidobacteria, Gammaproteobacteria, Planctomycetes, and WPS-2 were relatively abundant in Oi horizon, Bacteroidetes, Chloroflexi, Gemmatimonadetes, Verrucomicrobia and AD3 were abundant in Oe and OA horizons, and Actinobacteria, Bacteroidetes, Caldiserica, and Firmicutes were abundant in A horizon. In archaeal groups, Crenarchaeota accounted for approximately 80% from most soil layers. Although the relative abundance of Euryarchaeota was insignificant from total archaeal abundance, the relative abundance of Methanobacteria and Methanomicrobia increased below Oi horizon. Although many studies have emphasized the quantity of soil organic carbon, this study indicated that the soil quality is primary important factor that shapes microbial community structure as well as soil pH. In chapter 3, bacterial community in Arctic tundra soil was compared with Temperate and Tropical soils. According to a previous study, microbial community significantly interacted with specific soil properties. Thus, I identified the overall bacterial community structure and diversity between biomes, and assessed their relationship with soil properties. From the results of soil properties, Arctic soil was found to be relatively acidic and of nutrient rich environment, and Temperate and Tropical soil showed to be of low nutrient environment. Temperate soil showed highest richness and diversity, while Arctic soil showed the lowest richness and diversity. At phylum level, Acidobacteria and Alphaproteobacteria were predominant in all biomes. However, specific bacterial groups relatively abundant in each biome

the relative abundance of Verrucomicrobia and AD3 were dominant in Arctic soil, and Bacteroidetes and Betaproteobacteria were dominant in Temperate soil, and Chloroflexi, Cyanobacteria, and Ntrospirae were dominant in Tropical soil. Most dominant OTUs in all biomes play an important role in biogeochemical cycle in their habitat. Arctic and Tropical soil contained dominant OTUs, which contribute to the reducing of positive feedback of global warming. Although the sample size was limited, this study might help with advancing an understanding the biogeography of bacterial community at regional scales. The results in this study may contribute to extend our understanding about microbial community in moist acidic tundra soil, as well as help predict the microbial response to warming effect in Arctic soil.