Toward an understanding of microbial communities and biogeochemistry in high-elevation, unvegetated soils

Due to glacial retreat across the globe, soils at the highest reaches of mountain catchments are increasing in extent. Soils that are above the growth limit of most plants experience dramatic seasonal fluctuations in temperature and water availability, yet contain a microbial biomass that actively cycles carbon and nitrogen. The goal of this study was to understand how microbial communities at high-elevation function in the absence of plant primary productivity and to identify the composition of microbial communities in high-elevation, developing soils. Results showed that diverse communities of bacteria, eukarya and archaea were present. Photoautotrophic bacteria and microscopic green algae were identified and both CO2 fixation and respiration occurred. An estimated 24 g C m-2 yr-1 were brought into the soil via autotrophic activity during the short snow-free period, contradicting previous work that suggested this ecosystem is largely dependent on eolian deposition. Analysis of eukaryotic communities showed that chytrid fungi were more abundant in high-elevation, unvegetated soil of the Rockies and Himalayas than a majority of ecosystems on earth. Parasitism or saprobism of autotrophic organisms and pollen were shown to be the most likely means of survival for these fungi in high-elevation soil. Archaeal community analysis showed that archaea in high-elevation, unvegetated soils of the Rockies, Himalaya and Andes were almost entirely within the archaeal 16S rRNA group 1.1b and these sequences were closely related to a number of putative ammonia-oxidizing archaea. Additionally, both bacterial and archaeal ammonia monooxygenase genes were found in high-elevation, unvegetated soil, indicating the presence of ammonia oxidizers. Soil measurements throughout the snow-free period showed that seasonal patterns occurred in microbial biomass, nitrate and bacterial community composition, demonstrating the dynamic nature of this ecosystem. This study improves our understanding of the biogeochemistry of high-elevation, unvegetated soils and the microbial consortia found in this globally distributed soil environment.