WATER DEPTH CHANGES AND BIOMASS ALLOCATION IN 2 CONTRASTING MACROPHYTES

The response of B. arthrophylla and T. procerum in pot experiments to depth and depth changes provided insight into how plants survive fluct uating water levels. At 0 cm depth, most biomass was placed below grou nd, which can be interpreted as the placement of resource-acquiring ti ssues (roots, rhizomes) in resource (nutrients, space) -supplying envi ronments. At 50 and 100 cm, the placement of biomass into shoots recog nized the need for a higher supply of above-ground resources (light, i norganic carbon, oxygen). However, the responses of the two species to flooding or exposure differed. Rhizome storage supported an increase in the number and height of B. arthrophylla stems when flooded by 50 c m but this species was unable to counteract submergence to 100 cm with out the critical toss of root mass. The slow turnover rate of the cuti cularized B. arthrophylla stems indicates that biomass needs to be all ocated above water as well as above ground. Other responses indicated that this species may be better suited to seasonally fluctuating rathe r than permanent water levels. T. procerum dealt with water level chan ges via morphological plasticity. Along with the rapid growth and turn over of the spongy leaves, its shoot and total mass were maintained pr imarily from resources in the tubers.