Does living in elevated CO2 ameliorate tree response to ozone?: A review on stomatal responses

Short-term elevated 03 reduces photosynthesis, which reduces stomatal conductance (g,) in response to increased substomatal CO2 concentration (Q. Further exposure causes stomata to become sluggish in response to environmental stimuli. Exposure to elevated CO2 stimulates rapid stomata closure in response to increased Q. This reduction in gs may not be sustained over time as photosynthesis down-regulates and with it, g(s). The relationship between g, and photosynthesis may not be constant because stomata respond more slowly to environmental changes than photosynthesis, and because elevated CO2 may alter guard cell sensitivity to other signals. Also, reduced stomatal density (and g(s)) in response to long-term CO2 enrichment suggests sustained reduction in 9,. Elevated CO2 is believed to ameliorate the deleterious O-3 effects by reducing gs and thus the potential O-3 flux into leaves. Confirmation that g, acclimation to CO2 enrichment does not lessen over time is critical for developing meaningful O-3 flux scenarios. (c) 2005 Elsevier Ltd. All rights reserved.