Document: RON-3-30-7

Physiological adaptations of nine coniferous species of the northern Rocky Mountains to environmental change.

KOROL, R.L.*

USDA Forest Service, Rocky Mountain Research Station, Missoula MT, 59807 USA ¹

Abstract:
The efficiency with which trees use water is a major determinant of growth under water-limited conditions. This study investigated whether increased access to water and nutrients due to management practices alters the efficiency with which nine coniferous trees species use water. Intrinsic transpiration efficiency, defined here as the ratio of CO₂ assimilated and water transpired at a given vapor pressure deficit, is determined by the difference between the ambient atmospheric (c_a) and the intercellular CO₂ concentration within leaves (c_i). The mean value of c_i/c_a can be inferred from an analysis of carbon isotope discrimination () in wood samples. We measured carbon isotope ratios of wood samples from trees growing at a range of sites with widely varying soil and climatic conditions in the Inland northwest. Six hundred trees were cored and distinct annual rings were analyzed for their carbon isotope ratio. The selected trees represented a range of environmental (site) and stand conditions. We found that the inferred c_i/c_a decreased with decreasing water availability, which suggested that intrinsic transpiration efficiency increased with decreasing water availability. Discrimination varied by 4.0, which corresponds to a decrease in intrinsic transpiration efficiency of approximately 46%. Some species showed considerable variation or sensitivity to environmental change, while others had much less variation. Analyses of carbon isotope discrimination is a powerful technique that can be used to select genotypes with high intrinsic transpiration efficiency or to deduce responses of plants to changes in natural conditions, including global climate change. This technique may be valuable tool for predicting the migration of tree species to new areas as climate regimes are modified due to global climate change, due to management practices, or a combination of both.

Keywords: carbon isotopes, climate change, intrinsic transpiration efficiency

This abstract is being presented at: 9:30 AM in session:
Oral Session #43: Plant Community Responses to Climate Change.