Effects of cadmium on integration and resource allocation in the clonal fern Salvinia molesta

Summary

In clonal plants exposed to pollution, ramets which are physiologically integrated may be less fit than ramets which are independent, if (a) translocation of toxins from contaminated ramets produced toxicity, or (b) toxicity in parent ramets reduced the degree of nutritional support to otherwise non-exposed daughters. These hypotheses were tested in the aquatic fern Salvinia molesta exposed to cadmium. Pre-treatment of parent ramets with cadmium decreased the number and biomass of daughters subsequently produced in a cadmiumfree medium, because of reduced parental support of the first daughter generation. Second generation and later daughters were unaffected. Pre-treatment did not affect the pattern of integration (which, in terms of apical daughters' biomass, was bimodal with increasing colony size), or concentrations of essential elements in new growth. However, a diversion of resources from lateral to apical daughters occurred as a result of pre-treatment, especially in colonies with ≤3 attached parents. Loss/gain analysis showed that the diversion was almost reciprocal in terms of biomass, ramet numbers and phosphorus content. Integration between contaminated and uncontaminated ramets was not disadvantageous to the clone as a whole. However, integration was disadvantageous for Ca, Mg and Zn concentrations in daughters, which declined 15–22%. Because of enhanced apical growth, an indirect benefit of integration may be a more rapid fragmentation and dispersal of daughters from the site of contamination than if the parents were independent.