CONSTRUCTION COSTS FOR SOME AQUATIC PLANTS

Resource allocation reflects a plant's response to its environment and affects its overall growth and performance in a particular habitat. W e measured ash, C, N, and caloric content for various parts of Hydrill a verticillata (L.f.) Royle, Potamogeton nodosus Poir., P. gramineus L ., and P. pectinatus L. Mean ash content of vegetative propagules rang ed from 2.96 to 5.46%, lower than values previously reported for aquat ic plant shoots. Potamogeton propagule C and N contents were greater t han those of Hydrilla propagules. Mean propagule caloric content range d from 3753 to 4198 cal g(-1) and construction costs from 1.00 to 1.12 g glucose g(-1). They were similar to or slightly greater than those for shoots or leaves. Construction costs for leaves of eight aquatic s pecies averaged 1.02 g glucose g(-1). Vegetative propagules had sink s trengths similar to thoseVegetative propagules had sink strengths simi lar to those of shoots. H. verticillata, P. pectinatus, and P. gramine us were grown in a greenhouse with different levels of N in the water column. In this experiment, P. pectinatus and H. verticillata roots ha d higher construction costs than shoots whereas P. gramineus did not. Only the costs for P. pectinatus shoots and roots were affected by the N level in the water column. Construction costs for aquatic plant veg etative propagules, shoots, and roots were lower than similarly calcul ated values published for roots, stems and leaves of terrestrial plant s, in agreement with expectations based on the structural characterist ics of leaves and stems of aquatic plants.