Advances in molecular techniques have expanded our understanding of soil microbial communities, and raised important questions about regional and global patterns in microbial diversity. The proposed research will investigate the composition and activity of microbial communities across a range of geochemical and hydrologic soil conditions, and over local to regional scales in the Transantarctic Mountains, in order to assess controls over microbial biogeography. The research targets two areas in the Transantarctic mountains, the McMurdo Dry Valleys, and the Beardmore Glacier region further south, the latter representing an underexplored and inarguably more extreme soil environment. The research project will adopt an integrated approach, using molecular techniques and in situ assessment of biological activity in a quantitative biogeographical framework, with the goal of distinguishing fine versus broad scale controls over microbial community structure. The research is essential to determining the basic trophic status of extreme microbial food webs, and their sensitivity to climate change. The investigators will engage secondary and post-secondary educators through first person outreach as well as web-based communications and exercises. Two postdoctoral scientists will be trained in an interdisciplinary and international setting.
Soil microbes play an essential role in ecosystem function, worldwide. Microbes are the primary drivers of carbon and nutrient cycling in soil ecosystems, and are virtually the only actors in extreme ecosystems, such as soils in the Transantarctic Mountains. Therefore, to understand how expected changes in Antarctic environments potentially alter essential ecological functions, such as carbon and nutrient cycling, scientists must first have an understanding of the diversity and composition of microbial communities that are currently found in Transantarctic soils, and how well these microbial communities are mixed throughout the Transantarctic Mountains. To this end, the investigators designed a study to sample the soil microbial community over a very broad geographical region extending from the McMurdo Dry Valleys to ice-free areas in Meyer Desert (85 S) near the Beardmore Glacier, representing the southernmost observations of soil microbial communities to date (Fig. 1). A major challenge in this project was extracting microbial DNA from the extremely dry and saline soils representing the southernmost observations in Meyer Desert and similar locations. The investigators collaborated with scientists at the University of Waikato, NZ to develop molecular protocols to successfully extract and sequence DNA from some of the extreme locations. The investigators were able to successfully extract soil microbial DNA from less extreme habitats near Mt. Kyffin and the Cloudmaker, representing lower elevation sites near the mouth of the Beardmore Glacier, providing valuable information about the bacteria living in soils in the Beardmore Glacier region. Using fingerprinting techniques on bacterial 16S rDNA and a specific primer for cyanobacterial 16S rDNA, the investigators were able estimate among-site variation in microbial community composition, providing data to assess spatial models of soil microbial biodiversity. They found that cyanobacteria were a much rarer component of the bacterial community at southern sites, near the Beardmore Glacier, compared to the McMurdo Dry Valleys where cyanobacterial DNA was quite prevalent. Spatial patterns in the distribution of cyanobacterial groups also suggest dispersal from thick cyanobacterial mats near water bodies plays a large role in the distribution of cyanobacteria. Thus, the investigators suspect the prevalence of cyanobacteria, and levels of cyanobacterial diversity, are linked to the prevalence of prominent, biologically active water bodies (such as frozen ponds and lakes) throughout the landscape in the Transantarctic Mountains. The investigators' findings were extended with high-throughput amplicon sequencing of the V5-V6 region of 16S rDNA. They verified that Cyanobacterial abundance and diversity is high in soils that are near biologically active water bodies and identified a group of Cyanobacteria-associated bacteria that share a similar restricted distribution. The researchers then identified an Actinobacteria-dominated microbial assemblage that is ubiquitous and highly abundant in sites with no local water source, These bacteria responded to soil geochemical gradients, pH, soil moisture, soil N concentrations, and soil electrical conductivity, over regional spatial scales (i.e., environmental gradients spanning multiple Dry Valleys). The implications of these findings are that different components of the soil microbial community may have a capacity to respond to shifting environmental conditions over very different spatial scales. This means that the Actinobacteria-dominated microbial assemblage may exhibit a region-wide response to altered habitat conditions, whereas the cyanobacteria-dominated assemblages may be more closely tied to local shifts related to local habitat attributes, such as water levels in nearby lakes. Understanding the spatial scales that are relevant to microbial community composition, activity, and ultimately function, will provide a much better understanding of how shifts in climate can affect regional and global ecosystem services, such as carbon and nutrient budgets. As such, the investigators have been using the data gathered in this study along with data from other types of ecosystems across the NSF funded Long Term Ecological Research network in an effort to develop an ecological simulation program (MCSim, a metacommunity simulation program for the R statistical environment, maintained at https://github.com/sokole/MCSim) that can be used to test hypotheses about how environmental gradients and spatial attributes of the landscape are linked to biodiversity patterns, such as the ones observed here. This modelling framework is being developed to be able to make predictions about the spatial scales over which soil microbes are capable of responding to habitat shifts.
