Intraspecific variation of two duckweed species influences response to microcystin-LR exposure

Abstract Cyanotoxins produced by harmful cyanobacteria blooms can damage freshwater ecosystems and threaten human health. Floating macrophytes may be used as a means of biocontrol by limiting light and resources available to cyanobacteria. However, genetic variation in macrophyte sensitivity to cyanotoxins could influence their suitability as biocontrol agents. We investigated the influence of such intraspecific variation on the response of two rapidly growing duckweed species, Lemna minor and Spirodela polyrhiza , often used in nutrient and metal bioremediation. We assessed two biomarkers related to productivity (biomass and chlorophyll A production) and two related to fitness measures (population size and growth rate). Fifteen genetic lineages of each species were grown in media containing common cyanotoxin microcystin-LR at ecologically relevant concentrations or control media for a period of twelve days. Genotype identity had a strong impact on all biomarker responses. Microcystin concentration did impact the final population sizes of both macrophyte species with a marginal effect on growth rate of L. minor and the chlorophyll A production of S. polyrhiza , but overall these species were very tolerant of microcystin. The strong tolerance supports the potential use of these plants as bioremediators of cyanobacterial blooms. The differential impact of microcystin exposure discovered in single lineage models among genotypes indicates a potential for cyanotoxins to act as selective forces and reduce local macrophyte genetic diversity. Highlights Ecotoxicology often uses standard genotypes of plants in testing. We tested the influence of clonal variation in duckweeds on their response to common cyanotoxin, microcystin-LR. Microcystin impacts were often masked by genotypic variation in response. Results imply that genotype identity may be important to bioremediation and local evolutionary dynamics.