Modern molecular techniques have greatly increased our ability to identify bacteria. This has made it possible to investigate what controls the distribution of microbes and the composition of microbial communities, and to address fundamental questions about the roles that microbes play in essential ecological processes. Although current research is contributing to the recognition of geographic distribution patterns of microorganisms, the application of well-developed macroecological theory may provide insight to mechanisms underlying these patterns.
The influence of resource availability on soil bacterial communities will be examined within the McMurdo Dry Valleys of Antarctica. This region contains environmental gradients of nutrients, water, and salts which are predicted to strongly influence these simple, bacteria-dominated communities. Soil samples from 12 sites representing a natural gradient in above-ground production by moss and algae were collected in December 2010. DNA-based fingerprinting techniques applied to those samples revealed variation in bacterial community structure. Six of these soils will be resampled in 2012 and sequenced using both DNA- and RNA-based techniques to assess how bacterial community composition and metabolic activity are affected by resource availability. In addition, soil moisture and organic matter content will be experimentally manipulated to examine their interactive effects in structuring soil bacterial communities and their influence on microbial activity. This project will contribute to a greater understanding of mechanisms structuring bacterial communities and how this, in turn, may influence rates of ecosystem processes mediated by soil microorganisms. RNA-based methods also represent a novel approach for determining the active diversity of bacteria, a technique with potential value for investigating bacterial communities in all soils where a large proportion of the microbial community may be inactive.
This research will impact a broader audience by engaging undergraduate students in primary research and through interaction with both GK-12 outreach and an Antarctic study abroad programs currently operating at Virginia Tech.
The diversity of soil microbial communities is an important regulator of ecologically and economically important functions that occur in natural habitats, such as the rate of soil organic matter decomposition and recycling of critical nutrients necessary for maintaining soil fertility. As a consequence, understanding the factors that influence the diversity of microbial communities is important. Recent research has suggested that microbes may exhibit significant patterns in diversity according to the availability of resources, just as plant and animal communities do. This project investigated controls over the spatial organization of microbial communities and their influence on essential ecosystem processes, i.e., carbon cycling. The simple, microbially dominated soils of Antarctica’s McMurdo Dry Valleys were chosen as the ideal soils for examining clear effects of environmental drivers on bacterial diversity. Experimental results indicate that the availability of resources (e.g. organic carbon) is a primary limitation to the abundance and diversity of soil bacteria. Increasing organic matter availability is associated with an increase in the amount of bacterial biomass as well as greater diversity in microbial communities. However, bacterial communities become increasingly dominated by certain species at very high resource concentrations, suggesting competitive dominance. Varying the type of organic carbon amended to these soils also produced distinct shifts in the composition of bacterial communities, where certain species of bacteria grew preferentially in the presence of certain organic compounds. Results showed that microbial communities have distinct responses to environmental gradients structured by resource availability from those structured by environmental severity, or harshness. For example, richness of microbial communities was strongly correlated with organic matter availability, while microbial community composition exhibited the greatest variation over gradients structured by soil salinity and extremes in pH. Moreover, the results of this research demonstrated that both the type and amount of organic matter can have significant controls over the diversity and composition of soil bacterial communities, and subsequently influences the functions performed by these organisms. This funding supported the research and conference travel of one graduate student and the research of one undergraduate student, providing valuable skill training and collaborative opportunities for both. Results were communicated at multiple scientific conferences, a dissertation defense, two articles published in peer-reviewed journals and 2 additional manuscripts in development for publication in a scientific journal.
