Competition ecology of the dominant wetland macrophyte, Juncus effusus

Juncus effusus is among the most productive plant species worldwide. Extensive, persistent sediment seed banks formed during periods of environmental quiescence function in rapid colonization by J. effusus , and this early establishment has been suggested to provide the species a temporal competitive advantage during secondary succession. Furthermore, recent literature has suggested the potential for this species to affect neighboring species via release of potentially toxic chemical compounds from decaying tissues. Observational and experimental studies were conducted to evaluate which of the above traits of J. effusus were most likely responsible for observed competitive dominance of this species.; Experimental bioassays examined toxicity of dead, above-ground J. effusus tissues on three sedge (Cyperaceae) species and J. effusus itself, to determine whether autotoxic sensitivity was present. Results showed that species naturally occurring sympatric with, but subordinate to J. effusus, displayed little sensitivity to the tested extracts. However, growth of J. effusus seedlings was substantially suppressed when exposed to those extracts. This autotoxic inhibition of seedling development indicated that chemical interactions are not likely responsible for competitive inhibition of neighboring species by J. effusus.; Studies of dormancy, germination, and seed production of J. effusus were designed to evaluate the potential contribution of sexual reproduction to the competitive abilities of this species. Results demonstrated that seeds of J. effusus are non-dormant at maturity, but can be induced to dormancy when exposed to cold temperatures (4°C) or to reducing conditions typical of wetland sediments. These results indicate that sexual reproduction in this species functions in development of sediment seed reserves, possibly for use in future re-colonization of wetland areas after sediment disturbance.; Field investigations into competitive interactions between J. effusus and the surrounding plant community were performed during two growing seasons. Studies demonstrated negative effects of J. effusus on biomass and species richness of the surrounding plant community. Experimental manipulation of field study plots indicated that these negative effects resulted from J. effusus shading, and a mathematical model was developed to predict how results from studies of these isolated individuals of J. effusus might change as individual plants develop into an interacting population.