Axenic Culture and Nutritional Studies of Aquatic Macrophytes

Abstract

Studies were undertaken on nutritional factors regulating growth of aquatic macrophytes in calcareous lakes. Sterile cultures of species of Najas, Potamogeton, and Chara were not obtained employing methods that have been utilized in other investigations. Sterile culture techniques and rates of germination were improved by modification of media and conditions for growth. Rates of germination of Najas flexilis were inhibited by low light intensities and were increased markedly by exposure to mild heat treatment in darkness. Light quality, intensity, and duration have significant effects on the germination of Chara. Low light intensities in the visible spectral range provide more favorable conditions for germination. Germination of Najas was similar in both aerated liquid media and in agar of low redox gradients. Various cationic concentrations of the media did not appreciably alter germination of Najas and Chara. Brief treatment with indole-3-acetic acid (1000 mg 1-l) and gibberillic acid (100 mg 1-1) reduced germination markedly. Indirect evidence of chemoorganotrophic growth by Chara in the absence of light was found in the early stages of growth following germination. Rates of photosynthesis of axenic hydrophytes under varying nutrient concentrations were determined by rates of 14C bicarbonate uptake and radioassay of organic carbon in gas-phase. Photosynthetic rates of Najas flexilis were greatly reduced by Ca++ levels above 20 mg 1-F and inhibited by monovalent:divalent cation concentrations below one, in accord with prevailing unfavorable environmental conditions of parent calcareous lakes. Vitamin B-12, but not other water soluble vitamins, stimulated growth of Najas. Similar photosynthetic responses have been found among phytoplanktonic algae of marl lakes.