Physiological relationship between oil tolerance and flooding tolerance in marsh plants

• We hypothesized tolerance to oil exposure is related to flooding tolerance in plants.
• Oil exposure caused root oxygen deficiency in flooding sensitive species.
• Flooding tolerant plants showed no sign of oxygen deficiency under oil treatment.
• Photosynthesis is less sensitive to oil exposure compared to metabolism in roots.

Coastal salt marshes are highly susceptible to accidental oil spills. Oil can cover root tissues, inhibiting gas exchange and increasing root oxygen stress. This is similar to flooding; both conditions reduce the availability of oxygen to a plant. Therefore, it was hypothesized that tolerance to both flooding and oil are related in plants, as both impede gas exchange between roots and their environment. We investigated effects of oil on respiration and photosynthesis in nine marsh species ranging from flooding sensitive (hypothesized oil sensitive) to flooding tolerant (hypothesized oil tolerant). Plants were subjected to 6 L m−2 light motor oil in greenhouse experiments for six weeks. Oil exposure caused root oxygen deficiency in all but the most flooding tolerant species. Alcohol dehydrogenase activities increased in roots of flooding sensitive species and moderately flooding tolerant plants under oil exposure, indicating oxygen stress. In contrast, flooding tolerant plants showed no sign of oxygen deficiency under oil treatment. Additionally, decreases in photosynthetic rates were measured in some species following oil exposure. Photosynthesis was reduced by non-stomatal limitations, suggesting toxic effects of oil. It was concluded that tolerance to oil relates to flooding tolerance when measured in terms of biochemical enzyme activity. Root alcohol dehydrogenase activity was a sensitive indicator of oil susceptibility, whereas leaf-level photosynthesis was less sensitive to oil. Relating flooding and oil tolerance based on physiological measures could help future efforts to protect marsh plants prior to an oil spill as well as manage coastal marshes following an oil spill.