A seasonal study of growth characteristics and the levels of carbohydrates and proteins in Elodea nuttallii, polygonum amphibium and Phragmites australis

Abstract

Several growth characteristics of stands of Elodea nuttallii (Planch.) St. John, Polygonum amphibium L. and Phragmites australis (Cav.) Trin. ex Steud. were measured in situ. Virtually all biomass of E. nuttallii was located above ground all year, while a substantial portion occurred underground in Polygonum amphibium and Phragmites australis, the latter persisting in winter. The ratio surface area of aboveground biomass: total biomass was highest in E. nuttallii [0.1133 m 2g −1 ashfree dry weight (AFDW)] and far lower in both other species (0-0.007 m 2g −1 AFDW in Polygonum amphibium and 0-0.003 m 2g −1 AFDW in Phragmites australis). Chlorophyll occurred mainly in the epidermal cell layer, covering leaves and stems in E. nuttallii, but only the leaves of Polygonum amphibium and Phragmites australis. The average relative growth rates ( R ) varied from 0.019 in E. nuttallii to 0.008 in Polygonum amphibium and 0.009 g AFDW g −1 AFDW day −1 in Phragmites australis. The efficiencies of solar energy conversion were lower than in most terrestrial plants: 0.10% in E. nuttallii, 0.67% in Polygonum amphibium and 0.32% in Phragmites australis. The carbohydrate reserves were lower in E. nuttallii than in both other species. Starch was the principal component in E. nuttallii and in the underground organs of Polygonum amphibium and Phragmites australis, but sugars predominated in the aboveground biomass of both latter species. The respiratory requirement for growth early in the season was estimated to assess the plants' survival capacity. The carbohydrate reserves in E. nuttallii sufficed only for growth during 0.4 days, making the use of alternative reserves of protein likely. The energetic situation for Polygonum amphibium and Phragmites australis was more favourable: the carbohydrate reserves of the former sufficed for growth during 2.4 days and those of the latter for growth during 4.0 days. The performance of the three plant species in Lake Vechten is discussed.