Pathogen mediated diversity and response to climate change

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Fungal pathogens are thought to control biodiversity of forest trees through selective mortality of competitively dominant species that would otherwise threaten less competitive species. Climate warming may thus increase the extent and severity of disease. As pathogens increasingly survive mild winters, reproductive rates increase and plant defenses suffer from drought and temperature stress. This research will assess the extent to which pathogens regulate tree seedling health, identify the fungi involved and their effects on tree growth and survival, and determine how those interactions are affected by the temperature changes predicted for mid-century. The study will determine how temperatures affect their hosts when temperatures increase, within the context of simultaneous competition from other tree species, using a warming experiment where tree seedlings are exposed to soil and air temperature increases of 3°C to 5°C in North Carolina and Massachusetts. Once seedlings emerge, germination, survival, disease symptoms, and growth will be monitored. Pathogenic fungi and oomycetes residing on both seeds and seedlings will be identified using a combination of culture and DNA sequence-based methods. The effects of warming on pathogen incidence, infection, and seedling demography will be assessed using models that account for the combination of temperature, pathogens, and competition with other trees. By incorporating different sources of data into the analyses, this research will provide insight into the basic biology of forest risk as the natural capacity of trees to defend themselves changes under a warmer climate. The proposed research will provide insight into spatial and temporal dynamics of plant pathogens in natural systems, and how these dynamics might change under a warmer climate. An improved understanding of the diversity and composition of populations of plant pathogens and environmental factors can both enhance current management practices and inform models of future tree distributions. Teaching, training, and learning will be an integral part of this study, as it will require the assistance of undergraduate and high school students as work-study assistants and summer research technicians. In addition, a survey-based data collection component will be initiated to engage K-12 and the interested public, which combines this diversity research with outreach activities supported by Duke Forest. The results of this study will be disseminated to high school students during the annual Duke Forest Research Days, and to the general public in a series of forest pathology hikes in the Duke Forest.