COLLABORATIVE RESEARCH: How do seedlings survive? Hydraulics, carbon acquisition and drought tolerance in the earliest phases of tree growth

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Tree species distributions can shrink over time through reduced regeneration and subsequent adult mortality or they can expand via seedling establishment beyond current distribution boundaries. Therefore, a critical component of our ability to predict future species distributions is an understanding of the mechanisms of seedling establishment, which requires a fundamental knowledge of seedling physiology. The water pathway from the root to the leaf is critically important for maintaining leaf water status and allowing stomata to stay open, resulting in carbon capture through photosynthesis. However, water transport in the plant is vulnerable to desiccation-induced changes, including vascular tissue embolism (i.e. air bubble formation). The overall objective of this research is to understand the mechanisms responsible for prevention of hydraulic failure (i.e. catastrophic embolism) in tree seedlings, thereby ensuring adequate photosynthesis for their survival and establishment. Survival, growth, physiology and anatomy of growing seedlings will be measured to assess desiccation tolerance and the impacts of drying on photosynthesis, and to determine when structures that regulate seedling water loss develop. Results from this research can be directly used in modeled predictions of vegetation responses to climate change because seedling survival is likely a primary determinant of species distributions. These findings will also be of interest to policy makers and land managers who are interested in potential drought impacts on productivity and distributions of certain species. They will also be of interest to tree and woody crop breeders concerned with identifying traits associated with survival and adequate productivity in given environments. In addition, the ideas and methodology of measuring young seedling hydraulic parameters will be of interest to the plant science community and could provide a springboard for a new area of research activity. The project includes training of two graduate students, several undergraduate students and high school students.