GROWTH AND LEAF LIFE-SPAN OF A FLOATING-LEAVED PLANT, TRAPA NATANS L., AS INFLUENCED BY NITROGEN FLUX

Trapa natans L., cultured in tanks under varying nitrogen flux, was ex amined with particular reference to the change in foliage structure. L eaf initiation rate, leaf loss rate and leaf life-span were independen t of nitrogen flux and ranged from 140 to 250 mg N m(-2) day(-1). In c ontrast, leaf and rosette size were positively correlated with nitroge n flux. The maximum biomass was estimated to be 487 g dry weight m(-2) in the most nitrogen-enriched tank. With increasing nitrogen flux, pr oportions of petiole and reproductive parts (fruit) in the total bioma ss increased, while those of stem and root decreased. Net production o f T. natans was also positively correlated with nitrogen flux and rang ed from 5 to 14 g dry weight m(-2) day(-1) for all experimental tanks, excluding a tank with algal competition.