VEGETATIVE VARIATION OF MYRIOPHYLLUM-VARIIFOLIUM IN PERMANENT AND TEMPORARY WETLANDS

The responses of vegetative fragments of Myriophyllum variifolium J. Hooker to environmental variation in a field transplant trial are reported. Plant performance was measured as survival of plants, number of shoots and shoot length per surviving plant. Vegetative fragments from several lakes and different habitats within lakes were grown at three depths, in two regimes of disturbance by grazers and in two soils. The effect of depth was marked. Plants established and survived best on the shore (0-m depth) where their growth form was dominated by many shoots and prostrate spread. In contrast, plants in deeper water had low survival rates and surviving plants had single or few upright shoots. Separate analysis of the shore results indicated significant differences in plant performance between plants of various origin, between soil types and between regimes of disturbance by grazers. Plants originating from the deep water habitat consistently performed poorly whereas plants originating from the shore of the transplant site survived and grew well. Soil type had a major effect in the establishment phase of plant growth. Plants performed better on permanently wet basaltic soils (taken from the experimental transplant site) than on granitic soils from a temporary lagoon. The presence of grazing animals encouraged greater numbers and lengths of shoots on the shore. The role of flexibility in plant performance and vegetative reproduction in maintaining plant populations in lakes with unpredictable fluctuations of environmental conditions is discussed.