Importance of Nutrient Competition and Allelopathic Effects in Suppression of the Green Alga Scenedesmus obliquus by the Macrophytes Chara, Elodea and Myriophyllum

Abstract

Possible allelopathic effects of substances released from the macrophytes Chara globularis, Elodea canadensis, Myriophyllum spicatum on the common green alga Scenedesmus obliquus were tested in the laboratory with plastic plants and untreated medium as controls. A two-phase approach was used in which first the effects of physical presence of plants was studied (phase I) followed by the effects of plant culture filtrates (phase II). In the presence of plastic plants growth was reduced only marginally, but strong growth inhibition of Scenedesmus occurred in the physical presence of all macrophytes. In contrast, filtrates from Chara had no growth inhibitory effect on Scenedesmus. Myriophyllum filtrate reduced particle-based growth rate by 7% compared to filtration controls, while Elodea culture filtrate reduced volume-based growth by 12%, chlorophyll-based growth by 28% and particle-based growth by 15%. Photosystem IIefficiency of Scenedesmus was reduced in all three macrophyte treatments in phase I, but not in filtrates from macrophyte cultures (phase II). Thus, while enzyme activity or other physiological aspects may have been affected, the current study yielded no proof for allelopathically active compounds being directed at photosynthesis. Mean particle volume (MPV) of Scenedesmus was not influenced by macrophyte exudates and cultures remained dominated by unicells. The strong growth inhibitory effects found for Scenedesmus in the physical presence of macrophytes, but not in plastic controls, and no or weaker response in nutrientenriched filtrates, suggest nutrient competition was a more powerful driving factor than allelochemicals. However, the experimental design does not exclude disappearance of allelochemicals during the filtration process.

Searching for allelopathic effects of submerged macrophytes on phytoplankton—state of the art and open questions

“…Several authors wondered whether separating resource competition from allelopathy is at all realistic (Inderjit & del Moral, 1997;Lü rling et al, 2006;Lombardo et al, unpublished). Phosphorus and nitrogen limitation may affect the production and release of allelopathic compounds by submerged macrophytes (Gross, 2003b), as well as the response of the target organism (Reigosa et al, 1999).…”

Allelopathic interactions between the macrophyte Egeria densa and plankton (alga, Scenedesmus acutus and cladocerans, Simocephalus spp.): a laboratory study

“…In shallow waterbodies there exists an antagonistic relationship between phytoplankton and macrophytes. In macrophytic zones, low water turbulence, reduced light intensity and low nutrient concentrations in water limit phytoplankton growth (Lürling et al, 2006;Muylaert et al, 2010). However, macrophytes also affect plankton through the release of allelochemicals into the medium.…”

Allelopathic potential of stoneworts

“…Some other studies also suggested that low molecular weight substances could be allelopathically active (anthoni et al 1980;BanKova et al 2001;van donK & van de Bund 2002;lürling et al 2006;KuraShov et al 2014). BanKova et al (2001) identified some volatile compounds but did not test them separately for possible inhibitory effects.…”