Recent developments in DNA sequencing and molecular technologies have revolutionized the study of microorganisms, revealing their identities and genetic potential, and spawning new ecological concepts in microbial biodiversity. Spatial and temporal patterns in microbial species and their roles in natural ecosystems are controlled by their dispersal attributes (e.g., whether by wind or water) and local growth conditions, but the relative importance of these factors is unknown. This research will characterize these two fundamental controls on the distribution of microbes in Arctic lakes, streams and soils, and will reveal how seasonal, annual and long-term shifts in the populations of microbial species relate to the rapid climatic changes that are occurring in this region.
The complex nature of microbial biodiversity is important for understanding human health and disease, and for understanding the consequences of our warming world. Bacteria and other microbes ultimately control the production of carbon dioxide and methane, potent greenhouse gasses, in all ecosystems. In the Arctic there are currently low but rapidly increasing temperatures, thawing permafrost, and much accumulated organic matter all creating a situation ripe for increased bacterial respiration (conversion of organic matter to carbon dioxide). These collective factors could greatly alter regional and global carbon budgets, and hence feedback to further climate changes. This project will also contribute to teaching and outreach through the NSF Research Experience for Teachers program, the LTER-Schoolyard (K-12) program, and other field-based courses and mentoring programs.
Scientific Merit. Advances in technology and DNA sequencing have revolutionized the study of microorganisms such as bacteria, revealing their genetic identity and ecological potential, and spawning new concepts in microbial biodiversity. Microbial communities carry out critical processes that regulate the amounts and forms of important nutrients and carbon which are essential for all ecosystem services on Earth. We used a multi-year study of microbial community composition and growth rate in arctic lakes and streams on the North Slope of Alaska in order to measure how diversity and growth vary over time and are affected by global change. Results from the first five years of this research program demonstrate that the biodiversity and activity of these communities varies tremendously among environments and over time, and yet from year to year there is a predictable cycle of which microbial species dominate at any one time. We showed that changes in temperature and the amounts of nutrients interact to influence both the diversity and activity of microbial communities. In addition to these local environmental conditions that control bacterial growth and diversity, we found that the dispersal of microbes in wind and water was also important. For example, we found that microbes in lakes and streams are dominated by species that are present but rare on land, suggesting that uplands may serve as a seedbank for downslope microbial communities. Broader Impacts. The complex nature of microbial biodiversity and function is important for understanding human health and disease, and for understanding our warming world. Bacteria and other microbes ultimately control the production of the heat-trapping gases carbon dioxide and methane in all ecosystems. In the Arctic, warming temperatures are thawing permafrost and exposing a vast store of previously-frozen organic carbon in soils. If this carbon is released to the atmosphere as heat-trapping gases the rate of climate warming will increase, further thawing the soils and exposing more carbon to microbial attack. The strength of this positive feedback loop is controlled by bacteria, because their respiration converts the soil carbon to carbon dioxide and methane which is then released to the atmosphere. Thus the goal of this research project was to measure shifts in microbial biodiversity, bacterial respiration, and ecosystem function associated with the current and dramatic environmental changes in the Arctic. We found that bacteria are much more sensitive to changes in environmental conditions such as temperature or available nutrients than we had expected, and that bacterial communities composed of thousands of species in any habitat (lake, stream, soil) changed very rapidly when the environment changed. This rapid change in community composition translated into a substantial change in the activity of the community, and it is this activity that determines the rate at which microbes produce heat-trapping gases. Thus in order to understand how changes in the Arctic will feedback to climate changes in the rest of the world, we must continue to investigate and understand the diversity of microbes (by measuring which species dominate), how the diversity changes (by changing environmental conditions or by dispersal), and whether we can predict the rates of activity given what species we find. In addition, this project contributed to teaching and outreach through the NSF Research Experience for Undergraduates and Research Experience for Teachers programs (high school teachers), graduate student and postdoctoral scientist training, as well as presentations and articles in the popular press.
