Life histories of two clonal populations of Stratiotes aloides L.

Abstract

Life-history characteristics of two north Swedish populations of Stratiotes aloides L. are compared. On population consists of an emergent phenotype, living in a nutrient-rich lake. The other population is entirely formed by submersed plants, living in a nutrient-poor, riverside lagoon. Plants from each population transplanted to the other habitat showed that the emergent form was able to develop a submersed habit, whereas no significant change was observed in the submerged form.

The life cycle of the species is characterized by a winter-green period, during which the emergent form retained 36% and the submerged form 63% of its maximum biomass, respectively. Leaf turnover of both forms followed the same pattern, with successively increasing losses of old leaves during the growing season, resulting in an overwintering rosette made up of freshly-produced leaves. The number of turions and offsets produced by the emergent form is somewhat higher than those of the submerged form but the latter is suggested to allocate a greater proportion of energy to forming well-developed offsets. Under in situ experimental conditions during the growing season, the number of plants in both populations increased by 70% and no mortality was observed.

Concentration of potassium in the plant tissues of both forms increased throughout the growing season, that of calcium increased up to the time of peak biomass in August. The contents of phosphorus of the emergent plants transplanted to the lagoon decreased and the nitrogen content increased in relation to the mineral contents of the emergent plants in the lake. The opposite pattern in the contents of phosphorus and nitrogen was found for the submerged plants transplanted.