INFLUENCE OF SUBMERGENCE ON GROWTH OF SEEDLINGS OF SCIRPUS-LACUSTRIS AND PHRAGMITES-AUSTRALIS

1. Seeds of Scirpus lacustris and Phragmites australis were germinated in early June, and twenty-four seedlings of each species were subsequ ently exposed to submerged conditions (eight seedlings at each of the water depths 0.2, 0.4 and 0.8 m), in outdoor 500-l tanks in southern S weden. Weight and shoot length of the plants were measured in Septembe r. 2. The Phragmites seedlings did not show any significant growth whe n submerged. The Scirpus seedlings, however, developed submerged leave s and exhibited considerable submerged growth. One Scirpus plant, in s hallow water (0.2 m), had developed an aerial shoot by September. Shoo t length of the remaining (submerged) Scirpus plants was positively re lated to plant weight within water depth treatments, and was higher, i n relation to plant weight, in deeper water. Mean weight in September of the submerged Scirpus plants decreased with increased water depth. 3. In south Swedish lakes with a lowered water table, Scirpus often oc cupies large areas on the lakeward side of the reed belt, which is gen erally dominated by Phragmites. The differences between the two specie s, in performance of submerged seedlings, suggest that this zonation m ay be created through successful submerged seedling establishment of S cirpus on the lakeward side of Phragmites.