Decisions made based on that assumption may be inappropriate, Thackston argues. So he urges regulators to do the additional testing required to differentiate between the two causes of pollution so that they can make informed decisions on the matter. Our work has shown, for the first time, that, rather than causing the pores or stomates on a plant's leaves to close, as was generally assumed, ozone actually inhibits stomatal opening by directly affecting the 'guard cells' that control the opening. Plants take in the carbon dioxide they need for photosynthesis through their stomates, Torsethaugen explains. They also release oxygen made in photosynthesis through the same pores.
Ozone can enter the plant through the stomates and affect photosynthesis.
The Penn State experiments point to direct action on the guard cells as an additional path that ozone takes to reduce carbon dioxide use and decrease plant productivity. The Spalding's catchfly is a perennial herb with small greenish white flowers and foliage covered with sticky hairs. The plant is native to Palouse prairie habitats in southeastern Washington, northwestern Montana, and adjacent portions of Idaho, Oregon and British Columbia, Canada. The majority of remaining Spalding's catchfly populations are very small and isolated, often bordering adjacent agricultural fields or rangelands. A variety of factors have contributed to the plant's decline, including conversion of prairie into farmland, livestock grazing and trampling, fire suppression, and the effects of herbicides.