Plants transport, accumulate, and store the products of photosynthesis as nonstructural carbon (NSC), mainly in form of sugars and starch. These compounds provide energy for growth and maintenance of plant tissues, as well as for defense, reproduction and symbiosis. Existing research indicates that NSC plays a role in a plant's ability to compete and survive damage or stress. NSC also represents a significant fraction of a plant's annual C budget, contributing to interannual variation in stand-level productivity. Currently, models of NSC in plants are conceptual rather than quantitative, because we do not know how long C resides in these important forms. This project will use radiocarbon to measure the ages of starch and sugars extracted from stem wood as well as stem-respired CO2 in co-existing evergreen and deciduous oak trees (genus Quercus L.) in California. Oaks were chosen for their importance, for their different life strategies in the same climate situation, and because limits to their resilience will help determine their ability to survive disease and drought stress. NSC pools are predicted to be oldest where climate is least predictable (i.e. at the extremes of the species' ranges), and youngest where climate varies least from one year to the next. The role of NSC in plant survival will be explored by studying the age of CO2 respired by plants subjected to stresses like drought or defoliation (herbivory). The coming century will likely see increases in the stresses to which plants are exposed through climate change and increases in herbivory, fire or competition with invaders. NSC provides a major mechanism for plants to cope with stress and damage. The measurements made in this project will directly assess whether there are longer-term NSC stores accessible to plants, and the degree to which they use these stores to survive adverse conditions.
Broader impacts. The project has significant potential to increase our understanding of forest carbon pools and turnover. This is important in understanding plant response to climate change and in the earth's overall carbon budget. The project will support the training of graduate and undergraduate students in research. Members of a summer Research Experiences for Undergraduates program will participate and learn about the research. A summer course on the uses of radiocarbon in ecology that is the only one of its kind in the country is offered annually by the PI.
