Allelopathic effect on a nutrient-limited phytoplankton species

Abstract

For aquatic systems, studies on allelopathic interactions among phytoplankton have increased over recent years, with the main focus on the role of the donor organism. In this study, we report on the response of a target organism to allelochemicals and whether this response was affected by stress conditions (nutrient limitation). We exposed the diatom Thalassiosira weissflogii, grown under different nitrogen (N) and phosphorus (P) conditions (NP, -N, or -P), to single or daily additions of a cell-free filtrate of Prymnesium parvum (grown with no nutrient limitation). When we exposed T. weissflogii to a single addition of filtrate, all 3 treatments were inhibited by P. parvum. However, T. weissflogii NP was the most resistant, while T. weissflogii -N showed the highest sensitivity to P. parvum filtrate, followed by T. weissflogii -P. When T. weissflogii was exposed to daily additions of P. parvum, the degree of inhibition of all T. weissflogii treatments was higher than when only 1 initial addition was made. In this case, even the treatment that had the highest resistance (T. weissflogii NP) was not only inhibited by the filtrate, but also showed a decrease in cell numbers. Nevertheless, T. weissflogii -N was still more sensitive than the other treatments. Therefore, nutrient-limiting conditions may increase allelopathic effects, by making the target more susceptive to allelopathic compounds. Under these conditions, allelopathy may play a strong role in phytoplankton competition, especially in natural environments where the allelochemicals are continuously released and, thus, the target species do not have time to recover. KEY WORDS: Allelopathy · Phytoplankton · Target organism · Nutrient limitation · Thalassiosira weissflogii · Prymnesium parvum Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 41: [153][154][155][156][157][158][159][160][161] 2005 al. 1999), although few studies have really tested this hypothesis (Einhellig 1996) and those that did only concentrated on higher plants.Allelopathy is a form of interference competition, and, together with resource exploitation, it is used to explain patterns in plant competition dynamics (Rice 1984). Thus, factors that enhance the allelopathic effect may change the competitive balance towards allelopathic organisms. Since all plants and algae experience some kind of stress during growth, it is probable that the stress factors interact with allelopathy, thus changing the outcome of competition.In the present study, we investigated if the response of target phytoplankton species, which were exposed to allelochemicals, is affected by nutrient limitation. The fact that the allelopathic effect may be lost some time after exposure due to the degradation of the causative compounds was taken into consideration. Therefore, we also tested the response of nutrient-limited target species when exposed to a single addition of filtrate or to daily additions, and compared the results. Daily filtrate additions may better mi...

Native cover crops suppress exotic annuals and favor native perennials in a greenhouse competition experiment

“…Further, the annual cover crops might have been less effective, particularly against the perennial exotic species. Also, we might have observed more evidence of allelopathy, since allelopathic plants may produce more phytotoxins and target species may be more sensitive to allelochemicals when resources are scarce (Graneli and Johansson 2003;Fistarol et al 2005).…”

Effect of salinity on growth and chemical composition of the diatom Thalassiosira weissflogii at three culture phases

“…The value of microalgae as food source depends on some characteristics such as cell size and biochemical composition (Becker, 2004). In particular, the diatom Thalassiosira weissflogii (Fryxell & Hasle, 1977) has been widely used as live feed in aquaculture; however information related to its chemical composition is still scarce (Li, 1979;Emmerson, 1980;Fistarol et al, 2005). Environmental factors have been reported to influence the chemical composition of microalgae.…”

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

“…They concluded that allelopathic interactions between phytoplankton are an important aspect of competition. For example, cell-free filtrate from the prymnesiophyte Prymnesium parvum inhibits the growth of the diatom Thalassiosira weissflogii and the nutrient status of the diatom affects its response to the filtrate (Fistarol et al, 2005). The most common effects of allelochemicals are cell lysis and growth inhibition (Legrand et al, 2003).…”