Allelopathic activity of Stratiotes aloides on phytoplankton—towards identification of allelopathic substances

Abstract

The allelopathic activity of the aquatic macrophyte, Stratiotes aloides, was determined with laboratory experiments. Active compounds exuded in the medium or present in plant tissue were extracted using standard procedures and solid phase extraction (SPE). The activity towards various cyanobacteria and chlorophytes was tested in two different bioassay systems using agar plates and liquid cultures of phytoplankton. Extracts and exudates of S. aloides affected phytoplankton growth. SPE-enriched exudates and enriched water from a natural Stratiotes stand caused inhibition of target species, however, also some controls were active. Phytoplankton species exhibited differential sensitivity to extracts of S. aloides. We observed inhibitory and stimulatory effects on phytoplankton. In general, more cyanobacteria than other phytoplankton species were inhibited, and the inhibition of cyanobacteria was stronger. In most cases, nutrient (P or K) limitation of Synechococcus elongatus and Scenedesmus obliquus decreased the sensitivity of these species towards allelochemicals from Stratiotes aloides, except for P-limited cultures of Scenedesmus. The allelopathically active compound(s) from Stratiotes are moderately lipophilic and most likely no phenolic compounds. Our results indicate that allelopathy (besides nutrient interference and shading) might also account for the low phytoplankton and filamentous algae densities in the vicinity of Stratiotes plants, at least during certain phases of the life-cycle of Stratiotes.

Effects of Allelochemicals from Ficus microcarpaon Chlorella pyrenoidosa

“…In contrast, the inhibition rate of fraction A was poor, even lower than that of the control beginning on the third day, suggesting that fraction A stimulated the algal growth. The stimulation effect of fraction A, what we referred to as 'Hormesis', was similar to the results involving other plant extracts and allelochemicals (Nakai et al 1996;Körner and Nicklisch 2002;Mulderij et al 2007;Hong et al 2010). Fraction C showed the strongest inhibitory activity on the growth of algae, followed by fraction D, while fractions A and B boosted the algal growth inversely.…”

Can allelopathically active submerged macrophytes stabilise clear-water states in shallow lakes?

“…When pooling all available literature data on planktonic and epiphytic species (Hilt, 2006;Hilt et al, 2006;Mulderij, Mooij, Smolders, et al, 2005;Mulderij, Mau, et al, 2007), diatoms and cyanobacteria are often significantly inhibited by allelochemicals of submerged macrophytes, whereas chlorophytes appear less sensitive (Fig. 3).…”

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

“…Bioassay-directed extractions of Ceratophyllum demersum, Elodea spp., Myriophyllum spp., Najas marina and Stratiotes aloides with different solvents and solvent mixtures (water, methanol, and acetone; pure or mixed with water) often revealed the highest activity against cyanobacteria when solvents with intermediate lipophilic properties were used, e.g., 50% (v/v) acetone or 70% (v/v) methanol in water (Gross et al, 1996(Gross et al, , 2003Erhard & Gross, 2006;Mulderij et al, 2007). Under these conditions both hydrophilic and moderately lipophilic compounds can be extracted from the plant tissue.…”

“…Two other studies investigating allelopathic interactions between submerged macrophytes and phytoplankton pinned down nutrient effects. Synechococcus leopoliensis growth was enhanced in the presence of Elodea canadensis in a smallscale coexistence study, and inhibitory effects of allelochemicals from Stratiotes aloides declined when target species were nutrient limited (potassium or phosphorus limitation; Mulderij et al, 2007).…”

“…High nutrient concentrations (as often used in exudate experiments) may, however, counteract allelopathic inhibition of target species, thus potentially confounding the results. On the other hand, allelopathy experiments carried out at low nutrient levels may fail to show effects because target species may be nutrient limited in controls (Mulderij et al, 2007). As for other types of experiments, determinations of the availability of major nutrients (P, N), and possibly also micronutrients, is highly desirable in studies with exudates.…”