Abstract

Chara australis responded to changes in water levels by altering its morphology and allocation of resources. In a field harvest experiment, vegetative vigour of C. australis was greatest after water-level rises and the overall morphology of the plants varied depending upon season and site of collection. Allocation of dry weight varied over time, but allocation to sexual reproduction was always less than 10% of the total in this dioecious perennial species. C. australis reproduced sexually through the spring, summer and autumn, and where water levels were continually decreasing more female than male shoots were present. Field growth rates increased when depth was increased, and sexual reproduction was stimulated when water levels fell. An annual charophyte species (Nitella sonderi) did not display significant vegetative or sexual responses to water-level changes. The results of these experiments show that charophyte species can display morphological and reproductive plasticity in response to water level changes, although as charophytes are not uniform in their adaptations to fluctuations, results from one species cannot be extrapolated to another species. Life history could be a more important determinant of vegetative and reproductive characteristics than is phylogenetic affinity.