|Ground-level (tropospheric) ozone (O3) is the most significant phytotoxic gaseous pollutant in the eastern United States. Plants are subjected to acute and chronic exposures of tropospheric O3 that can cause foliar injury on sensitive plants as well as negative effects on a number of plant processes, including photosynthesis, rate of senescence, water use efficiency, dry matter production, pollen tube extension, flowering and yield.
Most of our knowledge about the effects of O3 on natural vegetation has come from studies conducted in controlled field experiments with open top chambers although this method has inherent technical problems and limitations that affect the applicability of results to ambient conditions. An alternative method is the use of protective chemicals such as ethylenediurea N-[-2-(2-oxo-1-imidizolidinyl) ethyl]-N’-phenylurea (EDU). EDU has been widely used to suppress acute and chronic O3 injury on agricultural crops and has been used to detect plant injuries, but comparatively little research has been conducted on native vegetation. The overall goal of this study was to assess visible injury, cell wall composition as related to nutritive quality, and biomass yield on native plants. It is hypothesized that EDU protects vegetation from ambient O3 concentrations, and therefore can be utilized as a diagnostic tool to assess damage to plant communities in natural environments. To achieve this goal, studies with cutleaf coneflower (Rudbeckia laciniata L.) and with purple coneflower (Echinacea purpurea) were constructed under controlled field conditions. They were exposed to different levels of O3 and treated by EDU. The results indicated that both plant species were sensitive to elevated ozone: significant changes occurred in biomass yield and cell wall constituents. Response to EDU alone was inconsistent. Higher concentrations of EDU appear to alleviate negative O3 effects on nutritive quality for purple coneflower. Increasing levels of EDU were observed to decrease the root and total biomass of cutleaf coneflower, indicating possible toxicity, however, higher concentrations of EDU did alleviate visible symptoms. Further testing is needed to determine if EDU is a useful tool for investigating ambient O3 effects under field conditions (no chambers).