ANATOMY OF CLOVER EXPOSED TO ENRICHED OZONE AND CARBON DIOXIDE

Authors: Fisher, Dwight; Heagle, Allen; Burns, Joseph

Submitted to: American Society of Agronomy Special Publication
Publication Type: Book / Chapter
Publication Acceptance Date: 8/23/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: In contrast to beneficial effects of ozone in the upper atmosphere in limiting ultraviolet radiation, ozone in the lower atmosphere results in more damage to plants than all other air pollutants combined. Two clones of white clover were selected based on how much they were damaged by ozone. Tests were made to distinguish the internal characteristics of NC-R and NC-S. Plants were exposed to a range of carbon dioxide and ozone before the anatomy was examined. Leaves and stems from each chamber were sampled and prepared for examination by microscope. Measurements were made of the thickness of the upper and lower cells of the leaf and the characteristics of the main vascular system for transporting water and sugars. The percent of open space inside the leaf was also estimated with the microscope. The susceptible plants had larger vascular systems but thinner leaves with less open space inside. The susceptible plants also had larger stems but a smaller percent of the area used for the vascular system. The differences in leaf dimensions and mesophyll density are probably related to the differential response to O3.

Technical Abstract: Overall, ozone (O3) pollution results in more damage to plants than all other air pollutants combined. Two clones of white clover were selected based on differential responses to O3 and described as O3 sensitive (NC-S) and O3 resistant (NC-R). Tests were made for distinguishing anatomical characteristics of NC-R and NC-S, as well as to examine the anatomy of these clones for responses to carbon dioxide (379 and 705 uL L-1) and O3 (17, 70, and 100 nL L-1) in greenhouse chambers. From each treatment, leaflets were sampled for image analysis. Measurements made on the leaves included; the thickness of the adaxial and abaxial epidermis, the depth and radius of the midrib, the perimeter and area of the midrib vascular bundle, and the area of the xylem tissue. The lamina thickness was measured and an index of mesophyll space was obtained by calculating the fraction of the image that consisted of space. The NC-S had larger midribs and vascular bundles but thinner leaves with a more dense mesophyll than NC-R. The differences in leaf dimensions and mesophyll density are probably related to the differential response to O3.