Environmentally Related Demography: Field Studies on Isoëtes Lacustris L. (Lycophyta, Isoëtaceae) in Europe

Abstract

At each population level studied (plant, leaf, and megaspore) a relationship between growth conditions and Isoëtes L. performance was recognized that is in the leaf number per rosette, leaf surface area, megaspore number and size. Leaf number per plant and variation coefficient proved to be dependent on plant density. Data of plant dry mass and density agrees with the weight-density relationship established by Duarte and Kalff (1987) for submersed plants. Dry mass ranges from 50 g/m² (in strenuous environment) to 175 g/m² (in optimal conditions). Four age states of plants were explained. Two distribution patterns of age/ life states are observed. In populations, experiencing optimal growth conditions, most plants are sporogenous, whereas most plants are in the infertile state in populations growing in non-optimal conditions. The rosette structure reflects seasonality as well as the growth conditions. The distinct variety of morphology and reproductive characteristics within a population suggests an individual life history performance according to plant vitality and environment. 1.