EVALUATION OF ROOT OXYGENATION AND GROWTH IN BALD-CYPRESS IN RESPONSE TO SHORT-TERM SOIL HYPOXIA

Seedlings of baldcypress (Taxodium distichum (L.) Rich. var. distichum) were grown under-laboratory and green-house conditions to determine the extent to which short-term soil hypoxia influences root aerenchyma - air space formation (expressed as a percentage of total root volume) and concomitant radial oxygen loss. Subsequent photosynthesis and growth responses were also determined. A colorimetric technique involving the use of Ti3+-citrate, a strong reducing compound, was used to quantify radial oxygen loss from whole root system. Soil redox potential of -250 +/- 10 mV resulted in enhancement of both root porosity and radial oxygen loss as much as 3-fold compared with plants under well aerated conditions (515 +/- 25 mV). The mean oxygen loss from roots was 1.4 mmol O2.g-1.day-1 in drained plants and 4.6 mmol O2.g-1.d-1 in flooded plants. Mean root porosity was 13.3 and 41.4% in drained and flooded plants, respectively. Stomatal conductance, net photosynthesis, and height growth were adversely affected by reduced soil conditions. Baldcypress exhibited an avoidance mechanism under reduced soil conditions by increasing aerenchyma formation and rhizosphere oxygenation at young ages. This may explain the significance of flooding episodes encountered in young stages in enabling baldcypress saplings and trees to tolerate flooding in later stages of the life cycle.