04/18/2011

Changing Water Balance in Forests Exposed to Elevated CO2

Summary

Plants influence ecosystem water balance through responses to environmental conditions, and their sensitivity to climate change could alter the ecohydrology of future forests. DOE scientists at Oak Ridge National Laboratory used a combination of measurements, synthesis of existing literature, and modeling to study the consequences of elevated CO₂ on ecohydrologic processes in forests. Data from five of DOE’s free-air CO₂ enrichment (FACE) sites reveal that elevated CO₂ reduced the passage of water vapor through the stomata, or small pores of the plant, leading to declines in canopy transpiration and water use for three closed-canopy forest sites. At the sweetgum FACE experiment in Oak Ridge, Tennessee, elevated CO₂ reduced seasonal transpiration by 10–16%. Model simulations also predicted reduced demand for water in response to elevated CO₂. The direct effect of elevated CO₂ on forest water balance through reductions in transpiration could be considerable, especially following canopy closure and development of maximal leaf area index. Complementary, indirect effects of elevated CO₂ include potential increases in root or leaf litter and soil organic matter, shifts in root distribution and altered patterns of water extraction.

References

Warren, J. M., E. Pötzelsberger, S. D. Wullschleger, P. E. Thornton, H. Hasenauer, and R. J. Norby. 2011. “Ecohydrologic Impact of Reduced Stomatal Conductance in Forests Exposed to Elevated CO₂,” Ecohydrology 4, 196–210. DOI: 10.1002/eco.173.