Allelochemical autotoxicity in the emergent wetland macrophyte Juncus effusus (Juncaceae)

Bioassays for allelochemical toxicity of aboveground Juncus effusus tissues were conducted with seeds and seedlings of Eleocharis obtusa and Scirpus c yperinus, two emergent sedge species (Cyperaceae) found sympatric with J. e ffusus, and with seeds and seedlings of J. effusus itself to evaluate poten tial autotoxicity. Bioassays were performed under controlled, axenic condit ions with aqueous shoot extract treatments simulating in situ dissolved org anic carbon concentrations. With respect to the two sedge species, neither shoot development nor seedling biomass accrual was significantly suppressed by lyophilized whole extracts from J. effusus. Although the extracts induc ed no significant reduction in growth of E. obtusa or S. cyperinus, biomass -specific chlorophyll a concentration was significantly reduced in E. obtus a seedlings. In contrast, seedlings of J. effusus exhibited significant red uctions of biomass and chlorophyll a concentrations, and seedling shoot dev elopment was retarded in response to leachate exposure. Results of the pres ent study suggest that J. effusus seedlings possess autotoxic sensitivity t o extracts of dead, aboveground tissues of adult plants.