DISSERTATION RESEARCH: Do accelerated microbial - organic matter interactions feed back to promote shrub growth in arctic tundra?

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The arctic holds the largest pool of soil carbon across land ecosystems. As the climate warms, changes to this carbon pool become increasingly important to understand. Carbon release from soils would increase concentrations of carbon dioxide in the atmosphere, while increases in soil carbon pools would remove carbon dioxide from the atmosphere. Higher temperatures have already trigged widespread expansion of large, woody shrubs across arctic tundra, and appear to stimulate the loss of soil carbon. This research examines whether shrubs change the composition of microbial communities in a way that positively impacts the shrub growth. This information is critical to understanding how shrubs affect carbon pools of plants and soils in the arctic. Using arctic soils from Alaska, the investigators will establish a plant growth experiment to determine how shrubs respond to different treatments of soil microbes and nutrients. By investigating plants, soils, and microbes in one experiment, this work will improve the accuracy of models of arctic carbon dynamics. In addition, this work will train undergraduates in both field and laboratory research skills and provide hands-on scientific experience. The results of this research will also be integrated into lesson plans for elementary, middle, and high school students through a collaboration between the researchers and local Georgia teachers. Previous research by these investigators demonstrates that shrubs promote a more active and less nutrient limited microbial community, which may lead to carbon loss from shrub soils. These findings suggest that shrubs stimulate soil microbial activity as a mechanism to improve nutrient availability, but it is unclear if shrub-induced changes to microbial communities benefit shrub growth. Using arctic soils, the researchers will establish a plant growth experiment using a fully factorial design crossing soil microbial source (shrub vs non-shrub) by nitrogen (+/-) and phosphorus (+/-) with a sterile control for three species of shrubs (Alnus fruticosa, Betula nana, and Salix pulchra). Collected data will include plant biomass, quantification of root symbioses, and soil microbial biomass. These data will be used to understand the magnitude and direction of shrub-microbial relationships and if carbon loss induced by microbial activity can be counterbalance by shrub carbon gain.