EVALUATION OF ROOT OXYGENATION AND GROWTH IN BALD-CYPRESS IN RESPONSETO 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 gr owth responses were also determined. A colorimetric technique involvin g the use of Ti3+-citrate, a strong reducing compound, was used to qua ntify radial oxygen loss from whole root system. Soil redox potential of -250 +/- 10 mV resulted in enhancement of both root porosity and ra dial oxygen loss as much as 3-fold compared with plants under well aer ated 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 floo ded plants. Mean root porosity was 13.3 and 41.4% in drained and flood ed plants, respectively. Stomatal conductance, net photosynthesis, and height growth were adversely affected by reduced soil conditions. Bal dcypress exhibited an avoidance mechanism under reduced soil condition s by increasing aerenchyma formation and rhizosphere oxygenation at yo ung ages. This may explain the significance of flooding episodes encou ntered in young stages in enabling baldcypress saplings and trees to t olerate flooding in later stages of the life cycle.