Competitive interactions between highly invasive Lemna minuta and Landoltia punctata at two nutrient levels.

  • Joëlle Gérard ((PhD) Student)
  • Ludwig Triest (Promotor)
  • Josphine Njambuya (Advisor)

Student thesis: Master's Thesis


A controlled indoor experiment was conducted to compare the performance of two alien Lemnaceae species both in monocultures and mixtures in high nutrient level (Hoagland solution) and low nutrient level (3 x diluted Hoagland solution). Lemna minuta is an invasive aquatic macrophyte native to America but has widely spread in Europe and has invaded many ponds in Belgium. Landoltia punctata on the other hand is a native to Australia and Southeast Asia that has been reported in The Netherlands. Lemnaceae can be transported over short distances by waterbirds and therefore, L. punctata will potentially invade ponds in Belgium. Studies on effects of invasive L. minuta on native L. minor are ongoing and preliminary results indicate competitive superiority of L. minuta over L. minor. Therefore, studies on performance of L. minuta and L. punctata in competition would shed light on which of the two invasive species is a superior competitor and hence enable us anticipate its future effects on the native species. Relative growth rate (RGR) of the two species and relative growth rate difference (RGRD) between the species was modeled to (1) reveal which of the two alien species is a superior competitor (2) determine what is the role of species identity, species initial biomass and nutrient enrichment in determining the composition change of these two species in mixture. Our results indicated stronger intraspecific relative to interspecific effects on the RGR of either species. As a result, species effects greatly influenced the difference in growth rate of both species. High nutrient level favored L. punctata relative to L. minuta and even at low nutrient level L. punctata had a relative advantage over L. minuta. Increasing the initial biomass of L. minuta enhanced RGRD while increasing the initial biomass of L. punctata had the opposite effect. These results indicate that species influence was the main determinant of change in this species mixture. RGR of both species tended to be higher in low nutrient level. This indicated that high nutrient level was too high for optimal growth. The low nutrient level was probably still too high. Therefore another experiment should be conducted in an even lower nutrient level (10 x diluted Hoagland solution). L. minuta seemed to compete by producing high amounts of small fronds. On the other hand L. punctata produced lesser, but larger fronds. We predict Landoltia punctata can potentially outcompete other Lemnaceae species.
Date of Award11 Sep 2009
Original languageEnglish
SupervisorLudwig Triest (Promotor) & Josphine Njambuya (Advisor)


  • Competition
  • Invasive
  • Aquatic weeds

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