Green Alga Desmodesmus Research Articles

Competitive adsorption in a ternary system of toxic metals and rare earth elements using Desmodesmus multivariabilis: empirical and kinetic modelling

The presence of competing metals in industrial wastewater creates problems of selectivity for binding sites during biosorption of cationic metallic species on microbial cell surfaces. For this reason, modelling of adsorption and uptake of multimetal solutions based on observation of performance of single metal species since this neglects the competition for reactive sites typical in multimetal solutions. In this study, a culture of the green alga Desmodesmus multivariabilis previously isolated from eutrophic freshwater was used as a biosorbent for adsorption/desorption of different metals in a mixed metal solution under varying environmental conditions. The Extended Langmuir Model (ELM) and Combined Langmuir and Freundlich Model (CLFM) were used to evaluate the data from a ternary metallic system. AQUASIM was used for optimization and simulation of kinetic data in ternary systems. The ELM performed better than CLFM with correlation coefficient of approximately 0.99. The highest uptake was observed for thallium with q max = 909.09 mg g−1 in single metal solution. This value was reduced to q max = 77.278 mg g−1 in the presence of other metals which demonstrated the competitive effects of other metal ions in solution. The q max value of lanthanum (La) decreased from 100 in single metals to 71.3 mg g−1 in multimetal solution; whereas, the q max = of cadmium (Cd) decreased from 48.5 to 40.1 mg g−1. Recovery of metals by D. multivariabilis was the highest for La at 90.92% followed by Cd at 90.15%. Competitive inhibition models provided a better insight on the potential for treatment of actual industrial wastewater with varying environmental factors.

Biogenic manganese oxides generated by green algae Desmodesmus sp. WR1 to improve bisphenol A removal

Biogenic manganese oxides (BioMnOx) have attracted considerable attention as active oxidants, adsorbents, and catalysts. This study investigated the characteristics of algae-generated BioMnOx and determined its oxidative activity towards bisphenol A (BPA), an endocrine disrupter. Amorphous nanoparticles with a primary Mn valency of +3 were found in BioMnOx produced by Desmodesmus sp. WR1. The mechanism might be that algal growth created conditions favorable to Mn oxidation through increasing DO and pH. Initial Mn2+ concentrations of 6, 30, and 50mgL−1 produced a maximum of 5, 13, and 11mgL−1 of BioMnOx, respectively. Mn2+-enriched cultures exhibited the highest BPA removal efficiency (∼78%), while controls only reached about 27%. BioMnOx may significantly promote BPA oxidation in algae culture, enhancing the accumulation of substrates for glycosylation. Moreover, continuous BioMnOx increase and Mn2+ decrease during BPA oxidation confirmed Mn oxide regeneration. In conclusion, Mn oxide formation by microalgae has the potential to be used for environmental remediation.

Production of lipid-containing microalgal biomass and simultaneous removal of nitrate and phosphate from synthetic wastewater

ABSTRACTThe major concerns of the modern society such as increasing population, climate change and economic development are imposing continuous stress on water and energy resources. The present work deals with the cultivation of green algae Desmodesmus abundans for optimum biomass productivity and lipid content as well as simultaneous removal of nitrate and phosphate from synthetic wastewater. The algal biomass is characterized by ultimate analysis, scanning electron microscopic analysis and thermogravimetric analysis. The effect of time, inoculum concentration and nitrate concentration on four responses (biomass productivity, lipid content, removal of nitrate and removal of phosphate) are studied by response surface methodology using central composite design. The quadratic models are found to be suitable for each response. At optimized experimental conditions, the algae showed biomass productivity of 46.96 mg L−1 day−1, lipid content of 16.23%, nitrate removal of 86.64% and phosphate removal of 87.52% after 27 days, when the initial inoculum concentration was 6% and nitrate concentration was 1.25 g L−1.

Identification of novel pathways for biodegradation of bisphenol A by the green alga Desmodesmus sp.WR1, combined with mechanistic analysis at the transcriptome level

The effects of bisphenol A (BPA) on the growth and photosynthetic activity of green alga Desmodesmus sp.WR1 were investigated, as well as its detoxification and biodegradation by this algal species. Transcriptome profiling analysis was employed to elucidate the molecular response of Desmodesmus to BPA exposure. None of the BPA exposure levels tested (1, 3, 5.5, 13.5mgL−1) significantly inhibited growth of Desmodesmus sp.WR1, and 57%, 25%, 18% and 26% of BPA were removed by this algal culture, respectively. The BPA metabolites monohydroxybisphenol A glycoside, 2-hydroxy-3-hydroxymethybisphenol A and its glycosides, and their monophenol products were identified for the first time as being generated from oxidative hydroxylation, glycosylation, and oxidative cleavage, respectively. Transcriptome analysis showed that algae significantly upregulated oxidoreductase- and glycosyltransferase-encoding genes for BPA oxidative biodegradation and addition of glycosyl groups for detoxification. This study suggests that the Desmodesmus sp.WR1 could be suitable for BPA removal from contaminated aquatic environments.

Transcriptome and physiological analysis of a lutein-producing alga Desmodesmus sp. reveals the molecular mechanisms for high lutein productivity

A green alga Desmodesmus sp. JSC3 is a lutein producer that appears high in lutein production in batch culture under 200μmol·m−2·s−1 condition using 1g∙L−1 sodium nitrate as nitrogen source. Because lutein content increased as growth advanced with the maximum (5.18mg∙g−1) on day 6, comparative transcriptome and physiological analyses on day 1, 6, and 8 were thus employed to uncover the molecular mechanisms for lutein production in this lutein producer. The gene set enrichment analysis using the False Discovery Rate (FDR) test showed that chlorophyll synthesis and photosynthesis were significantly changed when lutein accumulated. The up-regulation of the carotenogenesis genes explains the preference of this alga in lutein accumulation by enhancing lycopene synthesis and promoting metabolic flux towards synthesis of α-carotene and then hydroxylation of the β- and ε-ring of α-carotene, in the late exponential growth period (4–6days). Chlorophyll content and the expression of the genes encoding the enzymes in tetrapyrrole biosynthesis also increased during 0–6days, although chlorophyll a/chlorophyll b ratio decreased on day 6 due to light attenuation caused by high cell density. Photosynthetic activity and the expression of the genes encoding light-harvesting complex (LHC) proteins increased during 0–4days but decreased after that due to nitrogen deficiency (up-regulation of high-affinity nitrate transporter gene and low medium nitrate concentration). It suggests that LHC synthesis and photosynthesis are sensitive to nitrogen deficiency occurring on day 6 while pigment synthesis remains active. Because the expression of the genes encoding LHC-like proteins (early light-inducible proteins) that bind lutein and chlorophyll increased on day 6, LHC-like proteins could be temporarily stores of accumulating pigments. In conclusion, coordinate up-regulation of LHC-like proteins with pigment synthesis for the acclimation to decreasing light availability is believed as the molecular mechanism for high lutein production in Desmodesmus sp. JSC3.

Nutrient utilization traits vary systematically with intraspecific cell size plasticity

Summary Trait‐based approaches are increasingly used to help understanding community structure and ecosystem functioning. A large proportion of trait‐based studies define a species by its mean trait values and assume intraspecific trait variability to be negligible compared to interspecific differences. However, this assumption is rarely tested. Phenotypic cell size plasticity can be particularly important in phytoplankton species, which are known for their rapid changes in cell size in response to variations in environmental conditions. While phytoplankton traits show clear systematic trends with mean cell size across species, how size‐related plasticity influences the dynamics of a species remains unknown. In this study, we evaluate the effects of cell size plasticity on the nitrogen (N) utilization traits of the green alga Desmodesmus armatus (Chlorophyta), reared in different inorganic nitrogen sources (nitrate, ammonium or both) and nutrient histories (N‐replete and N‐deplete). Results show that traits for per‐cell ammonium uptake, maximum cell growth rate and minimum N‐quota change substantially within the study species, depending on mean cell size and nutrient history. In contrast, per‐cell nitrate uptake was independent of cell size. These results indicate that representing phytoplankton species only by their mean trait values could underestimate the physiological performance of a species by as much as one order of magnitude. This study highlights the extent to which explicit incorporation of within‐species trait variability can enhance our understanding of how species performance changes along environmental gradients. A lay summary is available for this article.

The effect of lanthanides on photosynthesis, growth, and chlorophyll profile of the green alga Desmodesmus quadricauda.

Lanthanides (La, Gd, Nd, Ce) accumulated in the green alga Desmodesmus quadricauda but their intracellular localizations were distinctly different: lanthanum and gadolinium were localized in cytoplasm, while neodymium and cerium were in the chloroplast. The effect of lanthanum and neodymium, as representatives of these two groups, on growth, chlorophyll content and photosynthetic rate at different light intensities was studied. At the lowest light intensity used (50µmol photons m-2s-1), in the presence of lanthanides (Nd), growth was enhanced by as much as 36% over lanthanide free control, and the photosynthetic rate increased by up to 300%. At high light intensities (238, 460, and 750µmol photons m-2 s-1), photosynthetic rate increased markedly, but there was no significant difference between rates in the presence or absence of lanthanides. However, growth, measured as a percentage of dry weight, if compared with lanthanide free control, increased at all light intensities (31, 39, and 20%, respectively). The total amount of chlorophyll after lanthanide treatment increased by up to 21% relative to the control culture, mainly due to an increase in the level of chlorophyll b. Addition of lanthanides caused a change in the chlorophyll a/b ratio from 4.583 in control cultivation, to 1.05. Possible mechanisms of lanthanide-induced photosynthetic change, alterations in photosynthetic structures, and increases in growth are discussed and compared with findings in higher plants. The hypothesis that the lanthanide effect could be due to formation of lanthanide-pheophytins was not confirmed as lanthanide pheophytins were not found in D. quadricauda. Furthermore, we have shown that the preferential incorporation of heavy isotopes of magnesium, namely 25Mg and 26Mg, into chlorophyll during photosynthesis that occurred in controls was diminished in the presence of lanthanides.

Uptake of caprolactam and its influence on growth and oxygen production of Desmodesmus quadricauda algae

The consumption of polyamides produced from caprolactam is increasing continuously, and for that reason the danger of environmental contamination by this lactam is also rising. This study's aim was to evaluate the influence of caprolactam on the growth and oxygen production of the green alga Desmodesmus quadricauda and on caprolactam uptake by this alga. The presence of caprolactam in water was observed to cause the algae significantly to increase its oxygen production. Caprolactam concentration of 5,000 mg/L stopped algae growth after 6 days and influenced coenobia structure (seen as disappearance of pyrenoids, deformation of cells) but did not decrease the number of cells in the coenobia. Caprolactam uptake is probably passive but relatively rapid. Maximum concentration in the algae was reached after 18–24 h.

COD and nitrogen removal from sugarcane vinasse by heterotrophic green algae Desmodesmus sp.

Vinasse is the main wastewater from the ethanol fermentation–distillation process, generated in large volumes during industrial sugarcane processing. Desmodesmus is a green algae genus with recognized ability to treat wastewater containing organic matter and to consume nutrients under heterotrophic growth conditions. Thus, the aim of this research was to evaluate Desmodesmus sp. growth in sugarcane vinasse. Results indicated slight elevation of pH, low oxygen, and low carbon dioxide consumption. Nitrogen and chemical oxygen demand (COD) removal were 52.1 and 36.2%, respectively. Specific growth rate of 0.15 h−1 and high yield of COD to biomass at first hour (0.5 mg mg−1) suggest the feasibility of biomass production of this green algae in sugarcane vinasse.

Growth Improvement of Nicotiana and Arabidopsis In Vitro by Microalgal Conditioned Media

Abstract Conditioned medium (CM) is a general term describing media in which cells have already been cultivated for some time. Such media, usually clarified by filtration, have been used by plant biotechnologists as additives sup-porting the growth of cell suspensions, organs and whole plants. This study examined the effect of CM obtained from green alga Desmodesmus subspicatus on the growth and functioning of the photosynthetic apparatus of Nicotiana tabacum and Arabidopsis thaliana in culture in vitro. Plants where cultured on CM diluted 1.25-, 2-and 5-fold with MS medium. The increase in fresh and dry weight was highest in tobacco and Arabidopsis cultured on CM/2 and CM/1.25 media. Those two concentrations also increased the amount of chlorophylls in both plants tested. CM improved parameter PI (reflecting the photosynthetic “vitality” of the organism) and electron transport efficiency, and increased the fraction of active reaction centers. Analysis of chlorophyll fluorescence in vivo suggests that the improvement of these plants grown in the presence of algal CM may result from stimulation of photosynthesis. Algal CM offers a convenient, cheap, universal supplement for stimulating the growth of higher plants in vitro.

Trace concentrations of iron nanoparticles cause overproduction of biomass and lipids during cultivation of cyanobacteria and microalgae

Cultivation in Zehnder medium containing 5.1 mg L−1 zero-valent iron nanoparticles (nZVI) boosted the growth of the green algae Desmodesmus subspicatus, Dunaliella salina, Parachlorella kessleri and Raphidocelis subcapitata and the eustigmatophycean algae Nannochloropsis limnetica and Trachydiscus minutus. In the cyanobacterium Arthrospira maxima, growth stimulation occurred at 1.7–5.1 mg L−1 nZVI. In all studied microorganisms, 5.1 mg L−1 nZVI strongly enhanced lipid accumulation, decreased the content of saturated and monounsaturated fatty acids with the exception of palmitoleic acid and increased the content of polyunsaturated fatty acids in cells. The nZVI particles may provide a suitable source of iron causing increased cell growth and induce metabolic changes resulting in higher lipid production and changes in fatty acid (FA) composition. Altered lipid synthesis may reflect the oxidative action of nZVI. Further research may contribute to optimizing the economical production of oils from oleaginous microorganisms and help clarify the mechanism of nZVI action.

Uptake, Elimination, and Biotransformation of 17α-Ethinylestradiol by the Freshwater Alga Desmodesmus subspicatus

Bioconcentration and transformation of the potent and persistent xeno-estrogen 17α-ethinylestradiol (EE2) by organisms at the basis of the food web have received only little research attention. In this study, uptake, elimination, and biotransformation of radiolabeled EE2 ((14)C-EE2) by the freshwater green alga Desmodesmus subspicatus were investigated. The alga highly incorporated radioactivity following (14)C-EE2 exposure. Up to 68% of the test compound was removed from the medium by D. subspicatus within a rather short time period (72 h C(algae)/C(water): 2200 L/kg wet weight). When the algae were transported to clear medium, a two-stage release pattern was observed with an initially quick elimination phase following slower clearance afterward. Interestingly, D. subspicatus brominated EE2 when bromide was available in the medium, a transformation process demonstrated to occur abiotically but not by algae. The consequence of the presence of more hydrophobic mono- and dibrominated EE2 in the environment remains to be further investigated, as these products were shown to have a lower estrogenic potency but are expected to have a higher bioaccumulation potential and to be more toxic than the mother compound.

Aquatic toxicity of the macrolide antibiotic clarithromycin and its metabolites

The human macrolide antibiotic clarithromycin is widespread in surface waters. Our study shows that its major metabolite 14-hydroxy(R)-clarithromycin is found in surface waters in comparable amounts. This metabolite is known to be pharmacologically active. Additionally, clarithromycin is partly metabolised to N-desmethyl-clarithromycin, which has no antimicrobial activity.For clarithromycin, some ecotoxicological studies on aquatic organisms have been published. However, many of them are not conform with the scientific principles as given in the “Technical guidance for deriving environmental quality standards” (TGD-EQS), because numerous studies were poorly documented and the methods did not contain analytical measurements confirming that the exposure concentrations were in the range of±20% of the nominal concentrations.Ecotoxicological effects of clarithromycin and its two metabolites on the zebrafish Danio rerio (embryo test), the microcrustacean Daphnia magna, the aquatic monocotyledonous macrophyte Lemna minor, the freshwater green alga Desmodesmus subspicatus (Chlorophyta) and the cyanobacterium Anabaena flos-aquae were investigated in compliance with the TGD-EQS. Environmental risk assessment was performed using ErC10 values of Anabaena, the species most sensitive to clarithromycin and 14-hydroxy(R)-clarithromycin in our testing. Based oncomparable toxicity and similar concentrations of clarithromycin and its active metabolite 14-hydroxy(R)-clarithromycin in surface waters, an additional multiplication factor of 2 to the assessment factor of 10 on the ErC10 of clarithromycin should be used. Consequently, a freshwater quality standard of 0.130μgL−1 is proposed for clarithromycin as the “lead substance”. Taking this additional multiplication factor of 2 into account, single monitoring of clarithromycin may be sufficient, in order to reduce the number of substances listed for routine monitoring programs.

Completion of cell division is associated with maximum telomerase activity in naturally synchronized cultures of the green alga Desmodesmus quadricauda

Telomerase maintains the ends of eukaryotic chromosomes, and its activity is an important parameter correlating with the proliferative capacity of cells. We have investigated cell cycle-specific changes in telomerase activity using cultures of Desmodesmus quadricauda, a model alga naturally synchronized by light/dark entrainment. A quantitative telomerase assay revealed high activity in algal cultures, with slight changes during the light period. Significantly increased telomerase activity was observed at the end of the dark phase, when cell division was complete. In contrast to other models, a natural separation between nuclear and cellular division typical for the cell cycle in D. quadricauda made this observation possible.

Promoting effects of organic medium supplements on the micropropagation of promising ornamental Daphne species (Thymelaeaceae)

Three Daphne species (Thymelaeaceae) were propagated in vitro using media enriched with natural ingredients including coconut water, pineapple pulp, arabinogalactan, chitosan, and conditioned medium containing exudates of the green alga Desmodesmus subspicatus. High vigor of proliferative shoots and enhanced rooting efficiency were obtained. The propagation rate for shoot cultures of Daphne caucasica and Daphne tangutica increased significantly when cultured in the presence of 10 ml L−1 coconut water or 10 ml L−1 pineapple pulp. Addition of 10 ml L−1 pineapple pulp, 10 ml L−1 coconut water, or 20% conditioned medium to the culture medium stimulated organogenesis in D. caucasica. The percentage of rooted shoots in this difficult-to-root species reached 80% in enriched medium. Daphne jasminea plants rooted efficiently on media without growth regulators but supplemented with 10 ml L−1 pineapple pulp or 10 ml L−1 coconut water. Plants of D. caucasica and D. jasminea were successfully acclimatized to greenhouse conditions. Biochemical evaluation of pineapple pulp using thin-layer chromatography revealed the absence of natural auxins. However, the low-molecular-weight fraction (<500 Da) obtained via dialysis significantly stimulated rhizogenesis in each species tested.

Bacterial community composition associated with freshwater algae: species specificity vs. dependency on environmental conditions and source community

We studied bacterial associations with the green alga Desmodesmus armatus and the diatom Stephanodiscus minutulus under changing environmental conditions and bacterial source communities, to evaluate whether bacteria-algae associations are species-specific or more generalized and determined by external factors. Axenic and xenic algae were incubated in situ with and without allelopathically active macrophytes, and in the laboratory with sterile and nonsterile lake water and an allelochemical, tannic acid (TA). Bacterial community composition (BCC) of algae-associated bacteria was analyzed by denaturing gradient gel electrophoresis (DGGE), nonmetric multidimensional scaling, cluster analyses, and sequencing of DGGE bands. BCC of xenic algal cultures of both species were not significantly affected by changes in their environment or bacterial source community, except in the case of TA additions. Species-specific interactions therefore appear to overrule the effects of environmental conditions and source communities. The BCC of xenic and axenic D.armatus cultures subjected to in situ bacterial colonization, however, had lower similarities (ca.55%), indicating that bacterial precolonization is a strong factor for bacteria-algae associations irrespective of environmental conditions and source community. Our findings emphasize the ecological importance of species-specific bacteria-algae associations with important repercussions for other processes, such as the remineralization of nutrients, and organic matter dynamics.

Flow cytometry as a diagnostic tool for the effects of polyphenolic allelochemicals on phytoplankton

We investigated the impact of the polyphenol tannic acid (TA) on the green algae Desmodesmus armatus and Scenedesmus vacuolatus and the diatom Stephanodiscus minutulus in order to find new diagnostic tools for allelopathic effects on phytoplankton. Esterase activity, membrane integrity and production of reactive oxygen species (ROS) were tested using flow cytometry with specific fluorescent markers. For comparison, growth rate and photosynthesis, two variables known to be affected by TA, were evaluated. Algae were exposed to TA concentrations between 0.6 and 30μmolL−1 for 3, 14 and 24h. A significant inhibition of esterase activity was detected at every time point in all three tested algal species at 30μmolL−1 TA and in most other treatments when TA concentrations exceeded 3μmolL−1. A significant production of ROS could also be detected in all three algal species, but only after a longer exposure period. Changes in membrane rigidity revealed no consistent patterns of enhancement or inhibition when tested with different TA concentrations, algal species and exposure time. Growth rates of all algae were significantly inhibited after 24h, whereas D. armatus was the only species for which the photosynthetic yield did not decline.The effects on esterase activity and ROS production indicate a general influence of polyphenolic allelochemicals on phytoplankton, but also reveal patterns which vary between species, concentrations and exposure times. Changes in esterase activity were the most sensitive variable, and could be detected after short exposure periods and at naturally occurring concentrations. Thus, esterase activity may be a suitable variable for future investigations into the allelopathic effects of submerged macrophytes on phytoplankton.

Phytotoxicity of Water and Sediment from Nif Brook (Izmir, Turkey) on Green Algae Desmodesmus (=Scenedesmus) Subspicatus

The water of Nif Brook (Izmir, Turkey) is polluted by industrial, domestic, and agricultural sources. As the water of the brook is used for domestic and industrial water supply as well as for irrigation, it is of great importance to know the toxicity potential for the natural populations. For this purpose the standard test protocol for the short term phytotoxicity test method OECD 201 Algal Growth Inhibition has been evaluated with cultures of green algae Desmodesmus (=Scenedesmus) subspicatus as the representative of the first trophic level. The test has been used to assess the toxicity of both water and sediment samples from the brook. Five sampling sites from the brook were selected considering the type of pollution sources. The water samples were tested with 10, 20, 40, 60, 80 and 100 % dilutions in a test medium. Extracts of sediment samples were assayed in three different concentrations (20, 40 and 100 mg/mL). The effects on the growth of D. subspicatus were evaluated by scoring cell numbers under the light microscope with a Neubauer haemocytometer counting chamber. According to the results, the water samples stimulated the algal growth (except station 1); although all sediment samples inhibited the growth of populations, in several grades.

Do macrophytes support harmful cyanobacteria? Interactions with a green alga reverse the inhibiting effects of macrophyte allelochemicals on Microcystis aeruginosa

Plant-released allelopathic substances are increasingly suggested as potential natural measure to control cyanobacteria blooms in lakes. We tested whether the common cyanobacterium Microcystis aeruginosa, known to be sensitive to allelochemicals, remains suppressed when interacting with a less sensitive green alga. We investigated the effects of polyphenolic allelochemicals on single and mixed cultures of the common green alga Desmodesmus armatus and M. aeruginosa with three different inoculum compositions. Polyphenols were added as tannic acid or released by a macrophyte (Myriophyllum verticillatum L.) in coexistence experiments with dialysis bags. Interaction with the green alga turned the inhibiting effect of allelochemicals on the cyanobacterium into an enhancement resulting in increased growth rates. The ratio between M. aeruginosa and the green alga consequently became significantly higher in treatments with allelochemicals as compared to controls after three days. When initial growth rates of M. aeruginosa and the green alga were similar, this resulted in an increasing abundance of the cyanobacterium under allelochemical presence. Interactions between phytoplankton species thus need to be taken into account when investigating the ecological relevance of macrophyte allelopathy and its potential to suppress cyanobacteria blooms.

COMPARISON OF METHODS TO DETECT ALLELOPATHIC EFFECTS OF SUBMERGED MACROPHYTES ON GREEN ALGAE(1).

Detecting allelopathic inhibition of phytoplankton by submerged macrophytes in an ecologically meaningful way is not easy. Multiple-approach investigations from a laboratory scale to the ecosystem level have been recommended to overcome the shortcomings of individual methods. Whether results of different methods are qualitatively or quantitatively comparable has not yet been tested. Here, we compare the sensitivity of the green algae Desmodesmus subspicatus (Chodat) E. Hegewald et Ant. Schmidt and Stigeoclonium helveticum Vischer to the allelopathic effect of the submerged macrophyte Myriophyllum verticillatum L. The following three approaches were used: (i) coincubation of algae in dialysis membrane tubes in a lake inside and outside a M. verticillatum stand, (ii) coincubation of algae in dialysis membrane tubes in aquaria with and without M. verticillatum, and (iii) single additions of tannic acid (TA), an allelopathically active polyphenol present in this macrophyte, to the algae cultures. For each method, fluorescence-based (chl a, PSII activity) and particle-based (cell count, biovolume) parameters were compared after 48 h of incubation. Results revealed quantitative and qualitative differences between methods. Algae incubated in dialysis membrane tubes in aquaria showed a strong decrease in all parameters under the influence of macrophytes. In situ measurements were influenced by adverse growth conditions for the test algae and only detected significant reductions for biovolume. Single additions of TA induced a strong reduction of fluorescence-based parameters similar to aquarium results, but an increase in the cell count. Even the qualitative transfer of laboratory results to field conditions thus requires caution and a proper selection of parameters.