Size-mediated foliar response to ozone in black cherry trees

Area of Science:

• Environmental Science
• Plant Physiology
• Forest Ecology

Background:

• Ozone is a significant air pollutant impacting vegetation.
• Black cherry (Prunus serotina Ehrh.) is a common tree species sensitive to ozone.
• Understanding ozone's impact on trees of different sizes is crucial for forest health.

Purpose of the Study:

• To assess the relationship between ozone exposure, uptake, and visible foliar injury in black cherry trees of varying sizes.
• To correlate visible injury symptoms with physiological responses like gas exchange.
• To identify effective ozone exposure indices for evaluating foliar injury.

Main Methods:

• Field measurements of ozone concentration and visible foliar injury on black cherry trees (seedlings, saplings, canopy trees) over a growing season.
• Leaf gas exchange measurements (stomatal conductance, net photosynthesis) were taken simultaneously with symptom observation.
• Analysis of relationships between injury, ozone exposure (Sum40, Sum60), and ozone uptake (stomatal conductance x concentration).

Main Results:

• Seedlings exhibited the highest percentage of leaf area affected by ozone injury (46%), followed by canopy (20%) and sapling (15%) trees.
• Seedlings had higher stomatal conductance, leading to greater ozone uptake, but larger trees showed more injury per unit of ozone uptake.
• Visible foliar injury was negatively correlated with net photosynthetic rates (r^2 = 0.82), indicating physiological impairment.

Conclusions:

• Seedlings are more susceptible to ozone injury due to higher ozone uptake rates.
• Ozone exposure indices like Sum40 and Sum60 effectively predict foliar injury.
• High levels of visible ozone injury disrupt the relationship between net photosynthesis and stomatal conductance in black cherry trees.