Effects of flood pre-conditioning on responses of three bottomland tree species to soil waterlogging

The potential for improving the performance of seedlings of woody species under flood stress was evaluated. Seedlings of baldcypress (Taxodium distichum), nuttall oak (Quercus nuttallii), and swamp chestnut oak (Quercus michauxii) were subjected to a two-phase study in which soil moisture regime was controlled. During Phase I, plants were randomly assigned to either: Control, well-watered and drained conditions; or intermittent flooding, alternating flooding and drained conditions. Following completion of Phase I, seedlings in each treatment were assigned randomly to one of two treatments: well-watered but drained or continuously flooded. Thus during Phase II, plants were divided into four groups: Control (A), intermittent flooding during Phase I and draining during Phase II (B), control during Phase I and continuously flooding during Phase II (C), and intermittently flooded during Phase I and continuously flooded during Phase II (D). Stomatal conductance (gw) in baldcypress increased in flooded treatments ranging from 112 to 128 percnt; of controls. Net photosynthesis (Pn) in baldcypress was not significantly affected by flooding while in oaks, Pn and gw decreased significantly in response to flooding. In oaks, flood pre-conditioning did not affect growth or physiological responses during phase II significantly. However, stomatal conductance of flood-hardened baldcypress was increased compared to seedlings that were not hardened. The study species developed significantly higher root porosity under flooded conditions compared to controls. Flood pre-conditioning did not appear to increase root porosity although it may have accelerated the process.