Leaf gas exchange and growth of flood-tolerant and flood-sensitive tree species under low soil redox conditions.

Seedlings of Taxodium distichum L., Quercus lyrata Walt. and Q. falcata var. pagodaefolia Ell. were grown for 22 days in a rhizotron system providing two soil redox potential regimes, +170 mV (low Eh) and +560 mV (high Eh). Leaf chlorophyll concentration and gas exchange, root alcohol dehydrogenase (ADH) activity, root and leaf ethylene production, and growth and biomass partitioning were measured. In response to the low Eh soil treatment, stomatal conductance was reduced in Q. falcata and Q. lyrata but not in T. distichum, whereas net photosynthesis was reduced significantly in all species; however, net photosynthesis in T. distichum began to recover within 2 weeks of treatment initiation. Within each treatment, mean stomatal conductance and net photosynthesis were significantly greater in T. distichum than in the oak species. Leaf chlorophyll concentration was not affected by the soil treatments. All species showed significant reductions in root and leaf dry weights in response to the low Eh soil condition. The low Eh soil treatment resulted in increased root ADH activity and ethylene production in T. distichum, but had no effect on root ADH activity and ethylene production in the oak species.