Validation of leaf ozone symptoms in natural vegetation using microscopical methods

Area of Science:

• Environmental Science
• Plant Pathology
• Ecology

Background:

• Ozone injury to natural vegetation is a growing concern across the Northern Hemisphere.
• A validated list of plant species exhibiting ozone-like symptoms is needed for accurate surveying.
• The International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP-Forests) requires new protocols for ozone impact assessment.

Purpose of the Study:

• To conduct a test survey of ozone injury on forest vegetation in Switzerland.
• To validate visible 'ozone-like' symptoms in various woody plant species.
• To investigate and confirm the origin of observed symptoms using specific plant response markers.

Main Methods:

• Surveying ozone injury in light-exposed forest sites across five Swiss ICP-Forests Level II plots.
• Assessing visible symptoms on 49 woody plant species during the year 2000, with accumulated ozone exposure over threshold (AOT40) ranging from 14 to 28 ppm-h.
• Investigating symptom origin in nine species and validating it in seven species using morphological, histological, and cellular markers indicative of oxidative stress and ozone response.

Main Results:

• Ten out of 49 surveyed woody plant species exhibited typical ozone-like symptoms, while four displayed untypical symptoms.
• Ozone effects were consistent across different taxonomic positions, characterized by induced oxidative stress in the mesophyll.
• Specific plant responses included light-dependent, hypersensitive-like reactions and accelerated cell senescence.

Conclusions:

• The study successfully validated ozone injury in seven woody plant species.
• A combination of cellular and morphological markers provides a reliable method for the differential diagnosis of visible ozone injury.
• Findings contribute to improved monitoring protocols for air pollution effects on forest ecosystems.