9630241 Reich The coniferous forests of boreal regions may be particularly affected by global environmental change. Temperature, photoperiod and CO2 levels may interact to profoundly influence the phenology (seasonal timing of development), net carbon exchange and growth of tree species. However, for any given tree species, populations from different regions may respond differently to global change. This possibility has been largely overlooked to date in scientific studies of vegetation response to global change. Thus, we do not understand how populations originating from diverse environments have adapted to climate, or whether diverse populations will respond similarly to altered temperature or CO2 concentrations. We will explore these issues in both laboratory and field experiments, using diverse seed sources of major boreal conifers: pine and spruce. We will test whether populations that are adapted to colder environments respond differently to altered temperature and CO2 levels than those from warmer environments. It is possible that trees originating in cold, stressed environments may be less responsive to global change, which could alter our attempts to globally model boreal ecosystems under global change. In controlled-environment studies, tree seedlings will be grown at present ambient (360 ppm) and future elevated (580 ppm) concentrations of CO2 in combination with a range of temperatures and two boreal photoperiods. Growth, phenology, and plant chemistry and physiology will be assessed. Field studies will involve plantations of older, mature jack pine and black spruce populations of broad biogeographic origin at several sites across a broad climate gradient in central North America. Field measures will include assessment of growth (from tree rings) and rates of photosynthesis and respiration. Development of models of shoot-growth phenology and of respiration as a function of tissue nitrogen and temperature will enable comparisons of seedling and mature tree responses . This research will examine the generality of patterns and mechanisms among boreal trees, improve models of carbon exchange, and increase our understanding of the role of biogeographic variation in vegetation response to potential global change.
