Abstract
The seasonal allocation of carbohydrates in water hyacinth was evaluated to determine the physiological weak points in the life cycle of this plant in three large, moderately polluted freshwater canals north of the Nile Delta (Egypt). Monthly plant samples were divided into laminae, petioles, stolons, stem-bases and roots to determine the seasonal changes in water-soluble carbohydrates (WSC), starch and total non-structural carbohydrates (TNC) for each plant organ. Generally, water hyacinth allocated 2.2% of its total biomass to stolons, 4.5% to stem-bases, 19.0% to roots, 21.1% to laminae and 53.1% to petioles. The proportion of biomass allocated to the root system (stolons, stem-bases and roots) decreased from 38.5% in April to 17.2% in July, while that of the shoot system (laminae and petioles) increased from 61.5% to 82.8% during the same period. Stem-bases were found to contain the highest concentrations of WSC, starch and TNC throughout the water hyacinth's life cycle. Starch represented the greatest part of the TNC pool, surpassing the concentration of WSC by 3.1- to 8.3-fold. The highest contents (g/m
2
) of WSC, starch and TNC were found in petioles. The period in the seasonal cycle when water hyacinth is expected to be most vulnerable to a control technique is when the carbohydrate contents are at the lowest. Based on the present study, this would be in April before complete mobilization of stored carbohydrates in the stem-bases and stolons have allowed expansion of the leaf material and the maximum growth rate.