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

Abstract

Allelopathy, here defined as biochemical interactions between aquatic primary producers, has always been intriguing as a process explaining the dominance of certain plant or algal species over others. Negative chemical interference has been invoked as one of the steering mechanisms behind mutual dominance of either submerged macrophytes or phytoplankton in shallow eutrophic lakes. Yet, despite much effort, convincing evidence for allelopathic interactions in situ is still missing. Also, laboratory approaches often lack reality. Inspired by a series of talks at the Shallow Lakes 2005 meeting in Dalfsen, the Netherlands, we argue that there is circumstantial but strong evidence that allelopathic interference between submerged macrophytes and phytoplankton may indeed exist in aquatic ecosystems despite the problems associated with research in this field. We first discuss experimental approaches combining laboratory and field studies, based on examples presented at this meeting. We then discuss the impact of nutrient status of both producing and target organism and biotic factors such as herbivory or pathogens that might affect allelopathy. Further topics are the potential seasonality of effects and the species-specificity of certain allelochemicals. We conclude with some thoughts why a final First publ. in: Hydrobiologia 584 (2007), pp. 77-88 proof for allelopathy in situ might remain difficult or even inaccessible in some cases, and why we nevertheless should not abandon this idea.

Allelopathy Inhibitory Effects of Hydrodictyon reticulatum on Chlorella pyrenoidosa under Co-Culture and Liquor-Cultured Conditions

“…Biological method is one of the most innovative technologies for environmental restoration in recent years, which has become a hotspot in the field of environment research [17][18][19][20][21][22]. Studies have shown that many kinds of aquatic plants have the ability to resist and control eutrophication, such as reed, Ceratophyllum demersum, Ruppia [4,[23][24][25]. Due to the advantages of high efficiency, low cost, and no secondary pollution, the method of algae control by plant allelopathy is of great significance for preventing and repairing water bodies from eutrophication [24,[26][27][28], and maintaining water stability after restoration.…”

Effect of removal of free-floating macrophytes on zooplankton habitat in shallow wetland

“…Consequently, we expect that the development of diverse types of macrophytes (submerged and free-floating) will create more physically complex habitats in aquatic ecosystems and support high zooplankton biodiversity. In contrast, extensive cover by free-floating macrophytes is expected to reduce underwater biomass as a result of shading effects (Gross et al, 2007). In other words, excessive growth of free-floating macrophytes would be expected to induce a relatively simple habitat structure, leading to a smaller, less diverse assemblage of zooplankton.…”

Seasonal variation in phytoplankton and aquatic plants in floodplain lakes (lower Vistula River, Poland)

“…In the water bodies where dominant macrophytes are observed, usually there is a strong competition for the resources of nutrients, light, and allelopathy observe (van Donk et al 1993;Scheffer and Jeppesen 1998;Gross et al 2007). Ma is an example of such reservoirs.…”

“…Oxbow lakes in this phase may even be compared to shallow macrophyte lakes (Scheffer and Jeppesen 1998;Scheffer and van Nes 2007). In oxbow lakes, competition occurs between phytoplankton and submerged vegetation, and accompanying vascular vegetation mats of filamentous algae-metaphyton (Gross et al 2007;Irfanullah and Moss 2005).…”