GROWTH AND MORPHOLOGICAL RESPONSES OF 4 HELOPHYTE SPECIES IN AN EXPERIMENTAL WATER-DEPTH GRADIENT

The distribution on shorelines of four helophyte species (two gramineo us species, viz. Phalaris arundinacea L. and Phragmites australis (Cav .) Trin. ex Steudel and two cyperacean species, viz. Scirpus maritimus L. and S. lacustris L.) was studied in relation to growth responses i n the water-depth gradient. Stands of S. lacustris were found at fewer depths relative to the mean water level (average fringe depth 69 +/- 19 cm) than stands of Phragmites australis (av. 45 +/- 20 cm), S. mari timus (av. 36 +/- 8 cm) and Phalaris arundinacea (av. 25 +/- 8 cm). Th e growth responses to a gradient of water depth were studied by planti ng the four species at five distinct water depths in outdoor basins, a nd determining morphological parameters and biomass distributions of t he species grown for two consecutive years. The biomass of Phalaris ar undinacea was reduced below 30 cm water depth, while Phragmites austra lis and S. maritimus showed reduced biomass at 80 cm water depth. S. l acustris showed no biomass reduction even at 80 cm water depth. An inc reased above-ground: below-ground biomass ratio in deeper water was de monstrated for each of the species under study; however, the modificat ion of biomass distribution in the gramineous species occurred abruptl y in very shallow water contrary to the cyperacean species. Mean basal stem diameter increased with water depth in all four species. Mean st em length increased with water depth in three of the four species. Ste m elongation with increasing water depth was strongest in the cyperace an species. The gramineous species showed enhanced formation of advent itious roots at submerged nodes. The similarity of responses to water depth was greatest within each of the groups of gramineous and cyperac ean species. The responses reflect the zonation of the species along t he water-depth gradient: S. lacustris in relatively deep water, Phragm ites australis and S. maritimus in shallower water, and Phalaris arund inacea in very shallow water.