Interference competition between Ludwigia repens and Hygrophila polysperma: two morphologically similar aquatic plant species

• Published in: Aquatic botany 2003-11, Vol.77 (3), p.223-234
• Main Authors: Doyle, Robert D., Francis, Matthew D., Smart, R.Michael
• Format: Article
• Language: English
• Subjects: Competitive interference; Exotic macrophyte; Freshwater; Hygrophila polysperma; Invasive species; Ludwigia repens; North America; River
• ISSN: 0304-3770; 1879-1522
• DOI: 10.1016/S0304-3770(03)00104-9

The interference competition between Ludwigia repens and Hygrophila polysperma was investigated in a 12-week tank experiment. In monoculture, sprigs (stem fragments) of both species showed similar growth rate and growth form. However, the two species differed strongly in response to interference competition from the other species. In response to increasing interference, sprigs of H. polysperma produced plants that had fewer but longer and more highly branched stems. However, the relative growth rate (RGR) was not significantly affected by the interference and total biomass accumulation was the same regardless of interference level. In contrast, developing sprigs of L. repens were negatively affected by interference. L. repens sprigs facing interference competition grew more slowly and produced fewer and shorter stems and fewer branches per stem than those growing in monoculture. At the highest level of interference, L. repens sprigs produced only 5% of the total mass produced when grown alone. Furthermore, the continued growth of established L. repens plants was significantly affected by interference from H. polysperma sprigs. At the end of the experimental growth period, the biomass of established L. repens invaded by H. polysperma sprigs was only 57% of that of established L. repens continuing to grow alone. Results of these experiments suggest that both species should effectively colonize unvegetated habitats. However, in an equal mixture of sprigs of the two species colonizing new habitats, H. polysperma will have advantage. Furthermore, established L. repens will be susceptible to invasion by H. polysperma while established H. polysperma is unlikely to be invaded by L. repens. The continued expansion of the exotic H. polysperma in North America is predicted.