The Science

Summer heat waves cause damage to leaves and stems in temperate forest ecosystems, affecting the short- and long-term survival of plants. Scientists at Oak Ridge National Laboratory studied and detailed the response and recovery of several southeastern tree species after short-term heat waves. By monitoring specific trait behavior, the research team characterized each tree’s reaction to being kicked into survival mode for brief periods of time and found that different tree species display varying degrees of photosynthetic damage, primarily to chlorophyll systems.

The Impact

The research team found that heat-induced damage to a key photosynthetic mechanism [photosystem II (PSII)] could serve as a good mechanistic trait and indicator to improve projections of how different species respond to extreme weather events.

As heat waves continue to occur, and even strengthen in the future, improved understanding of the sensitivity of different species to extreme temperatures will allow for better predictions of heat wave effects on species distribution and ecosystem function under changing environmental conditions.

Summary

Scientists gained new insights about the mechanisms and thresholds for damage among tree species enduring short-term heat waves. This new knowledge could fill a gap in current simulations of forest growth response to shifting environmental conditions. Current models do not address the variability in response between co-occurring tree species to temperature extremes. To address this, the team exposed sets of saplings from southern red oak, Shumard oak, tulip-poplar, and eastern white pine to dramatic temperature swings that peaked at 51°C in a climate-controlled test chamber. Sensors attached to each tree and located throughout the chamber tracked indicators of heat and drought stress such as fluxes in carbon uptake, shifts in water demand, and changes in chlorophyll fluorescence and PSII activity. A significant increase in both transient and chronic damage to PSII within the leaf chloroplasts was evident in the most heat sensitive species, pine and tulip poplar. The oaks, especially southern red oak, showed greater tolerance to heat and rapid overnight recovery. The findings indicate that differential heat-induced damage to PSII within the leaf chloroplasts may be a mechanistic trait that can be used to project how different species respond to extreme weather events, improving predictions of forest response to extreme temperatures.

Principal Investigator

Anirban Guha
Oak Ridge National Laboratory
guha2009anirban@gmail.com

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

Support was through the Terrestrial Ecosystem Science program of the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science, and by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for DOE under contract DEAC05-00OR22725.

Related Links

• Oak Ridge National Laboratory Story Tip

References