TY - GEN A1 - Chorus, Ingrid A1 - Spijkerman, Elly T1 - What Colin Reynolds could tell us about nutrient limitation, N:P ratios and eutrophication control T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Colin Reynolds exquisitely consolidated our understanding of driving forces shaping phytoplankton communities and those setting the upper limit to biomass yield, with limitation typically shifting from light in winter to phosphorus in spring. Nonetheless, co-limitation is frequently postulated from enhanced growth responses to enrichments with both N and P or from N:P ranging around the Redfield ratio, concluding a need to reduce both N and P in order to mitigate eutrophication. Here, we review the current understanding of limitation through N and P and of co-limitation. We conclude that Reynolds is still correct: (i) Liebig's law of the minimum holds and reducing P is sufficient, provided concentrations achieved are low enough; (ii) analyses of nutrient limitation need to exclude evidently non-limiting situations, i.e. where soluble P exceeds 3-10 mu g/l, dissolved N exceeds 100-130 mu g/l and total P and N support high biomass levels with self-shading causing light limitation; (iii) additionally decreasing N to limiting concentrations may be useful in specific situations (e.g. shallow waterbodies with high internal P and pronounced denitrification); (iv) management decisions require local, situation-specific assessments. The value of research on stoichiometry and co-limitation lies in promoting our understanding of phytoplankton ecophysiology and community ecology. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1344 KW - phytoplankton KW - nitrogen limitation KW - redfield ratio KW - co-limitation KW - enrichment experiments Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-541979 SN - 1866-8372 IS - 1 ER - TY - JOUR A1 - Wilhelms, Andre A1 - Börsig, Nicolas A1 - Yang, Jingwei A1 - Holbach, Andreas A1 - Norra, Stefan T1 - Insights into phytoplankton dynamics and water quality monitoring with the BIOFISH at the Elbe River, Germany JF - Water N2 - Understanding the key factors influencing the water quality of large river systems forms an important basis for the assessment and protection of cross-regional ecosystems and the implementation of adapted water management concepts. However, identifying these factors requires in-depth comprehension of the unique environmental systems, which can only be achieved by detailed water quality monitoring. Within the scope of the joint science and sports event "Elbschwimmstaffel" (swimming relay on the river Elbe) in June/July 2017 organized by the German Ministry of Education and Research, water quality data were acquired along a 550 km long stretch of the Elbe River in Germany. During the survey, eight physiochemical water quality parameters were recorded in high spatial and temporal resolution with the BIOFISH multisensor system. Multivariate statistical methods were applied to identify and delineate processes influencing the water quality. The BIOFISH dataset revealed that phytoplankton activity has a major impact on the water quality of the Elbe River in the summer months. The results suggest that phytoplankton biomass constitutes a substantial proportion of the suspended particles and that photosynthetic activity of phytoplankton is closely related to significant temporal changes in pH and oxygen saturation. An evaluation of the BIOFISH data based on the combination of statistical analysis with weather and discharge data shows that the hydrological and meteorological history of the sampled water body was the main driver of phytoplankton dynamics. This study demonstrates the capacity of longitudinal river surveys with the BIOFISH or similar systems for water quality assessment, the identification of pollution sources and their utilization for online in situ monitoring of rivers. KW - water quality KW - phytoplankton KW - river dynamics KW - multisensor system KW - online KW - monitoring KW - high spatial resolution KW - multivariate statistics Y1 - 2022 U6 - https://doi.org/10.3390/w14132078 SN - 2073-4441 VL - 14 IS - 13 PB - MDPI CY - Basel ER - TY - JOUR A1 - Ehrlich, Elias A1 - Thygesen, Uffe Høgsbro A1 - Kiørboe, Thomas T1 - Evolution of toxins as a public good in phytoplankton JF - Proceedings of the Royal Society of London : B, Biological sciences N2 - Toxic phytoplankton blooms have increased in many waterbodies worldwide with well-known negative impacts on human health, fisheries and ecosystems. However, why and how phytoplankton evolved toxin production is still a puzzling question, given that the producer that pays the costs often shares the benefit with other competing algae and thus provides toxins as a 'public good' (e.g. damaging a common competitor or predator). Furthermore, blooming phytoplankton species often show a high intraspecific variation in toxicity and we lack an understanding of what drives the dynamics of coexisting toxic and non-toxic genotypes. Here, by using an individual-based two-dimensional model, we show that small-scale patchiness of phytoplankton strains caused by demography can explain toxin evolution in phytoplankton with low motility and the maintenance of genetic diversity within their blooms. This patchiness vanishes for phytoplankton with high diffusive motility, suggesting different evolutionary pathways for different phytoplankton groups. In conclusion, our study reveals that small-scale spatial heterogeneity, generated by cell division and counteracted by diffusive cell motility and turbulence, can crucially affect toxin evolution and eco-evolutionary dynamics in toxic phytoplankton species. This contributes to a better understanding of conditions favouring toxin production and the evolution of public goods in asexually reproducing organisms in general. KW - toxic algal blooms KW - evolution of cooperation KW - coexistence KW - patchiness in KW - phytoplankton KW - eco-evolutionary feedback KW - spatial pattern formation Y1 - 2022 U6 - https://doi.org/10.1098/rspb.2022.0393 SN - 0962-8452 SN - 1471-2954 VL - 289 IS - 1977 PB - Royal Society CY - London ER - TY - JOUR A1 - Chorus, Ingrid A1 - Spijkerman, Elly T1 - What Colin Reynolds could tell us about nutrient limitation, N:P ratios and eutrophication control JF - Hydrobiologia : acta hydrobiologica, hydrographica, limnologica et protistologica N2 - Colin Reynolds exquisitely consolidated our understanding of driving forces shaping phytoplankton communities and those setting the upper limit to biomass yield, with limitation typically shifting from light in winter to phosphorus in spring. Nonetheless, co-limitation is frequently postulated from enhanced growth responses to enrichments with both N and P or from N:P ranging around the Redfield ratio, concluding a need to reduce both N and P in order to mitigate eutrophication. Here, we review the current understanding of limitation through N and P and of co-limitation. We conclude that Reynolds is still correct: (i) Liebig's law of the minimum holds and reducing P is sufficient, provided concentrations achieved are low enough; (ii) analyses of nutrient limitation need to exclude evidently non-limiting situations, i.e. where soluble P exceeds 3-10 mu g/l, dissolved N exceeds 100-130 mu g/l and total P and N support high biomass levels with self-shading causing light limitation; (iii) additionally decreasing N to limiting concentrations may be useful in specific situations (e.g. shallow waterbodies with high internal P and pronounced denitrification); (iv) management decisions require local, situation-specific assessments. The value of research on stoichiometry and co-limitation lies in promoting our understanding of phytoplankton ecophysiology and community ecology. KW - phytoplankton KW - nitrogen limitation KW - redfield ratio KW - co-limitation KW - enrichment experiments Y1 - 2020 U6 - https://doi.org/10.1007/s10750-020-04377-w SN - 0018-8158 SN - 1573-5117 VL - 848 IS - 1 SP - 95 EP - 111 PB - Springer Nature CY - Berlin ER - TY - JOUR A1 - Ehrlich, Elias A1 - Gaedke, Ursula T1 - Coupled changes in traits and biomasses cascading through a tritrophic plankton food web JF - Limnology and oceanography N2 - Trait-based approaches have broadened our understanding of how the composition of ecological communities responds to environmental drivers. This research has mainly focussed on abiotic factors and competition determining the community trait distribution, while effects of trophic interactions on trait dynamics, if considered at all, have been studied for two trophic levels at maximum. However, natural food webs are typically at least tritrophic. This enables indirect interactions of traits and biomasses among multiple trophic levels leading to underexplored effects on food web dynamics. Here, we demonstrate the occurrence of mutual trait adjustment among three trophic levels in a natural plankton food web (Lake Constance) and in a corresponding mathematical model. We found highly recurrent seasonal biomass and trait dynamics, where herbivorous zooplankton increased its size, and thus its ability to counter phytoplankton defense, before phytoplankton defense actually increased. This is contrary to predictions from bitrophic systems where counter-defense of the consumer is a reaction to prey defense. In contrast, counter-defense of carnivores by size adjustment followed the defense of herbivores as expected. By combining observations and model simulations, we show how the reversed trait dynamics at the two lower trophic levels result from a "trophic biomass-trait cascade" driven by the carnivores. Trait adjustment between two trophic levels can therefore be altered by biomass or trait changes of adjacent trophic levels. Hence, analyses of only pairwise trait adjustment can be misleading in natural food webs, while multitrophic trait-based approaches capture indirect biomass-trait interactions among multiple trophic levels. KW - community ecology KW - cyclops vicinus KW - dynamics KW - functional traits KW - lake KW - life-cycle KW - natural rotifer KW - phytoplankton KW - trophic cascades KW - zooplankton Y1 - 2020 U6 - https://doi.org/10.1002/lno.11466 SN - 0024-3590 SN - 1939-5590 VL - 65 IS - 10 SP - 2502 EP - 2514 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Van den Wyngaert, Silke A1 - Seto, Kensuke A1 - Rojas-Jimenez, Keilor A1 - Kagami, Maiko A1 - Grossart, Hans-Peter T1 - A New Parasitic Chytrid, Staurastromyces oculus (Rhizophydiales, Staurastromy-cetaceae fam. nov.), Infecting the Freshwater Desmid Staurastrum sp. JF - Protist N2 - Chytrids are a diverse group of ubiquitous true zoosporic fungi. The recent molecular discovery of a large diversity of undescribed chytrids has raised awareness on their important, but so far understudied ecological role in aquatic ecosystems. In the pelagic zone, of both freshwater and marine ecosystems, many chytrid species have been morphologically described as parasites on almost all major groups of phytoplankton. However, the majority of these parasitic chytrids has rarely been isolated and lack DNA sequence data, resulting in a large proportion of "dark taxa" in databases. Here, we report on the isolation and in-depth morphological, molecular and host range characterization of a chytrid infecting the common freshwater desmid Staurastrum sp. We provide first insights on the metabolic activity of the different chytrid development stages by using the vital dye FUN (R)-1 (2-chloro-4-[2,3-dihydro-3-methyl-[benzo-1,3-thiazol-2-yl]-methylidene]-1-phenylquinolinium iodide). Cross infection experiments suggest that this chytrid is an obligate parasite and specific for the genus Staurastrum sp. Phylogenetic analysis, based on ITS1-5.8S-ITS2 and 28S rDNA sequences, placed it in the order Rhizophydiales. Based on the unique zoospore ultrastructure, combined with thallus morphology, and molecular phylogenetic placement, we describe this parasitic chytrid as a new genus and species Staurastromyces oculus, within a new family Staurastromycetaceae. (C) 2017 Elsevier GmbH. All rights reserved. KW - Chytrids KW - parasite KW - phytoplankton KW - Staurastromyces oculus KW - Staurastrum sp. Y1 - 2017 U6 - https://doi.org/10.1016/j.protis.2017.05.001 SN - 1434-4610 VL - 168 SP - 392 EP - 407 PB - Elsevier CY - Jena ER - TY - GEN A1 - Zimmermann, Heike Hildegard A1 - Stoof-Leichsenring, Kathleen Rosemarie A1 - Kruse, Stefan A1 - Müller, Juliane A1 - Stein, Ruediger A1 - Tiedemann, Ralf A1 - Herzschuh, Ulrike T1 - Changes in the composition of marine and sea-ice diatoms derived from sedimentary ancient DNA of the eastern Fram Strait over the past 30 000 years T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The Fram Strait is an area with a relatively low and irregular distribution of diatom microfossils in surface sediments, and thus microfossil records are scarce, rarely exceed the Holocene, and contain sparse information about past richness and taxonomic composition. These attributes make the Fram Strait an ideal study site to test the utility of sedimentary ancient DNA (sedaDNA) metabarcoding. Amplifying a short, partial rbcL marker from samples of sediment core MSM05/5-712-2 resulted in 95.7 % of our sequences being assigned to diatoms across 18 different families, with 38.6 % of them being resolved to species and 25.8 % to genus level. Independent replicates show a high similarity of PCR products, especially in the oldest samples. Diatom sedaDNA richness is highest in the Late Weichselian and lowest in Mid- and Late Holocene samples. Taxonomic composition is dominated by cold-water and sea-ice-associated diatoms and suggests several reorganisations – after the Last Glacial Maximum, after the Younger Dryas, and after the Early and after the Mid-Holocene. Different sequences assigned to, amongst others, Chaetoceros socialis indicate the detectability of intra-specific diversity using sedaDNA. We detect no clear pattern between our diatom sedaDNA record and the previously published IP25 record of this core, although proportions of pennate diatoms increase with higher IP25 concentrations and proportions of Nitzschia cf. frigida exceeding 2 % of the assemblage point towards past sea-ice presence. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1195 KW - last glacial maximum KW - surface temperatures KW - species composition KW - greenland shelf KW - Disko Bay KW - phytoplankton KW - communities KW - variability KW - diversity KW - Svalbard Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-525154 SN - 1866-8372 IS - 5 ER - TY - JOUR A1 - Zimmermann, Heike Hildegard A1 - Stoof-Leichsenring, Kathleen Rosemarie A1 - Kruse, Stefan A1 - Müller, Juliane A1 - Stein, Ruediger A1 - Tiedemann, Ralf A1 - Herzschuh, Ulrike T1 - Changes in the composition of marine and sea-ice diatoms derived from sedimentary ancient DNA of the eastern Fram Strait over the past 30 000 years JF - Ocean Science N2 - The Fram Strait is an area with a relatively low and irregular distribution of diatom microfossils in surface sediments, and thus microfossil records are scarce, rarely exceed the Holocene, and contain sparse information about past richness and taxonomic composition. These attributes make the Fram Strait an ideal study site to test the utility of sedimentary ancient DNA (sedaDNA) metabarcoding. Amplifying a short, partial rbcL marker from samples of sediment core MSM05/5-712-2 resulted in 95.7 % of our sequences being assigned to diatoms across 18 different families, with 38.6 % of them being resolved to species and 25.8 % to genus level. Independent replicates show a high similarity of PCR products, especially in the oldest samples. Diatom sedaDNA richness is highest in the Late Weichselian and lowest in Mid- and Late Holocene samples. Taxonomic composition is dominated by cold-water and sea-ice-associated diatoms and suggests several reorganisations – after the Last Glacial Maximum, after the Younger Dryas, and after the Early and after the Mid-Holocene. Different sequences assigned to, amongst others, Chaetoceros socialis indicate the detectability of intra-specific diversity using sedaDNA. We detect no clear pattern between our diatom sedaDNA record and the previously published IP25 record of this core, although proportions of pennate diatoms increase with higher IP25 concentrations and proportions of Nitzschia cf. frigida exceeding 2 % of the assemblage point towards past sea-ice presence. KW - last glacial maximum KW - surface temperatures KW - species composition KW - greenland shelf KW - Disko Bay KW - phytoplankton KW - communities KW - variability KW - diversity KW - Svalbard Y1 - 2019 VL - 16 IS - 5 PB - Springer CY - Tokyo ER - TY - JOUR A1 - Van den Wyngaert, Silke A1 - Rojas-Jimenez, Keilor A1 - Seto, Kensuke A1 - Kagami, Maiko A1 - Grossart, Hans-Peter T1 - Diversity and Hidden Host Specificity of Chytrids Infecting Colonial Volvocacean Algae JF - Journal of Eukaryotic Microbiology N2 - Chytrids are zoosporic fungi that play an important, but yet understudied, ecological role in aquatic ecosystems. Many chytrid species have been morphologically described as parasites on phytoplankton. However, the majority of them have rarely been isolated and lack DNA sequence data. In this study we isolated and cultivated three parasitic chytrids, infecting a common volvocacean host species, Yamagishiella unicocca. To identify the chytrids, we characterized morphology and life cycle, and analyzed phylogenetic relationships based on 18S and 28S rDNA genes. Host range and specificity of the chytrids was determined by cross-infection assays with host strains, characterized by rbcL and ITS markers. We were able to confirm the identity of two chytrid strains as Endocoenobium eudorinae Ingold and Dangeardia mamillata Schroder and described the third chytrid strain as Algomyces stechlinensis gen. et sp. nov. The three chytrids were assigned to novel and phylogenetically distant clades within the phylum Chytridiomycota, each exhibiting different host specificities. By integrating morphological and molecular data of both the parasitic chytrids and their respective host species, we unveiled cryptic host-parasite associations. This study highlights that a high prevalence of (pseudo)cryptic diversity requires molecular characterization of both phytoplankton host and parasitic chytrid to accurately identify and compare host range and specificity, and to study phytoplankton-chytrid interactions in general. KW - Chytridiomycota KW - Dangeardia mamillata KW - Endocoenobium eudorinae KW - fungal parasites KW - life cycle KW - phytoplankton Y1 - 2018 U6 - https://doi.org/10.1111/jeu.12632 SN - 1066-5234 SN - 1550-7408 VL - 65 IS - 6 SP - 870 EP - 881 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Beisner, Beatrix E. A1 - Grossart, Hans-Peter A1 - Gasol, Josep M. T1 - A guide to methods for estimating phago-mixotrophy in nanophytoplankton JF - Journal of plankton research N2 - Growing attention to phytoplankton mixotrophy as a trophic strategy has led to significant revisions of traditional pelagic food web models and ecosystem functioning. Although some empirical estimates of mixotrophy do exist, a much broader set of in situ measurements are required to (i) identify which organisms are acting as mixotrophs in real time and to (ii) assess the contribution of their heterotrophy to biogeochemical cycling. Estimates are needed through time and across space to evaluate which environmental conditions or habitats favour mixotrophy: conditions still largely unknown. We review methodologies currently available to plankton ecologists to undertake estimates of plankton mixotrophy, in particular nanophytoplankton phago-mixotrophy. Methods are based largely on fluorescent or isotopic tracers, but also take advantage of genomics to identify phylotypes and function. We also suggest novel methods on the cusp of use for phago-mixotrophy assessment, including single-cell measurements improving our capacity to estimate mixotrophic activity and rates in wild plankton communities down to the single-cell level. Future methods will benefit from advances in nanotechnology, micromanipulation and microscopy combined with stable isotope and genomic methodologies. Improved estimates of mixotrophy will enable more reliable models to predict changes in food web structure and biogeochemical flows in a rapidly changing world. KW - flow cytometry KW - phagotrophy KW - phytoplankton KW - methods KW - fluorescence KW - microscopy KW - FISH KW - isotopic methods KW - phylotypes KW - carbon flows KW - gene sequencing Y1 - 2019 U6 - https://doi.org/10.1093/plankt/fbz008 SN - 0142-7873 SN - 1464-3774 VL - 41 IS - 2 SP - 77 EP - 89 PB - Oxford Univ. Press CY - Oxford ER - TY - GEN A1 - Bolius, Sarah A1 - Morling, Karoline A1 - Wiedner, Claudia A1 - Weithoff, Guntram T1 - Genetic Identity and Herbivory Drive the Invasion of a Common Aquatic Microbial Invader T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Despite the increasing number of species invasions, the factors driving invasiveness are still under debate. This is particularly the case for “invisible” invasions by aquatic microbial species. Since in many cases only a few individuals or propagules enter a new habitat, their genetic variation is low and might limit their invasion success, known as the genetic bottleneck. Thus, a key question is, how genetic identity and diversity of invading species influences their invasion success and, subsequently, affect the resident community. We conducted invader-addition experiments using genetically different strains of the globally invasive, aquatic cyanobacterium Raphidiopsis raciborskii (formerly: Cylindrospermopsis raciborskii) to determine the role of invader identity and genetic diversity (strain richness) at four levels of herbivory. We tested the invasion success of solitary single strain invasions against the invader genetic diversity, which was experimentally increased up to ten strains (multi-strain populations). By using amplicon sequencing we determined the strain-specific invasion success in the multi-strain treatments and compared those with the success of these strains in the single-strain treatments. Furthermore, we tested for the invasion success under different herbivore pressures. We showed that high grazing pressure by a generalist herbivore prevented invasion, whereas a specialist herbivore enabled coexistence of consumer and invader. We found a weak effect of diversity on invasion success only under highly competitive conditions. When invasions were successful, the magnitude of this success was strain-specific and consistent among invasions performed with single-strain or multi-strain populations. A strain-specific effect was also observed on the resident phytoplankton community composition, highlighting the strong role of invader genetic identity. Our results point to a strong effect of the genetic identity on the invasion success under low predation pressure. The genetic diversity of the invader population, however, had little effect on invasion success in our study, in contrast to most previous findings. Instead, it is the interaction between the consumer abundance and type together with the strain identity of the invader that defined invasion success. This study underlines the importance of strain choice in invasion research and in ecological studies in general. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 971 KW - alien species KW - genotype KW - invasibility KW - cyanobacteria KW - consumptive resistance KW - phytoplankton KW - Raphidiopsis KW - genetic diversity Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-474333 SN - 1866-8372 IS - 971 ER - TY - JOUR A1 - Bolius, Sarah A1 - Karoline Morling, A1 - Wiedner, Claudia A1 - Weithoff, Guntram T1 - Genetic Identity and Herbivory Drive the Invasion of a Common Aquatic Microbial Invader JF - Frontiers in Microbiology N2 - Despite the increasing number of species invasions, the factors driving invasiveness are still under debate. This is particularly the case for “invisible” invasions by aquatic microbial species. Since in many cases only a few individuals or propagules enter a new habitat, their genetic variation is low and might limit their invasion success, known as the genetic bottleneck. Thus, a key question is, how genetic identity and diversity of invading species influences their invasion success and, subsequently, affect the resident community. We conducted invader-addition experiments using genetically different strains of the globally invasive, aquatic cyanobacterium Raphidiopsis raciborskii (formerly: Cylindrospermopsis raciborskii) to determine the role of invader identity and genetic diversity (strain richness) at four levels of herbivory. We tested the invasion success of solitary single strain invasions against the invader genetic diversity, which was experimentally increased up to ten strains (multi-strain populations). By using amplicon sequencing we determined the strain-specific invasion success in the multi-strain treatments and compared those with the success of these strains in the single-strain treatments. Furthermore, we tested for the invasion success under different herbivore pressures. We showed that high grazing pressure by a generalist herbivore prevented invasion, whereas a specialist herbivore enabled coexistence of consumer and invader. We found a weak effect of diversity on invasion success only under highly competitive conditions. When invasions were successful, the magnitude of this success was strain-specific and consistent among invasions performed with single-strain or multi-strain populations. A strain-specific effect was also observed on the resident phytoplankton community composition, highlighting the strong role of invader genetic identity. Our results point to a strong effect of the genetic identity on the invasion success under low predation pressure. The genetic diversity of the invader population, however, had little effect on invasion success in our study, in contrast to most previous findings. Instead, it is the interaction between the consumer abundance and type together with the strain identity of the invader that defined invasion success. This study underlines the importance of strain choice in invasion research and in ecological studies in general. KW - alien species KW - genotype KW - invasibility KW - cyanobacteria KW - consumptive resistance KW - phytoplankton KW - Raphidiopsis KW - genetic diversity Y1 - 2019 U6 - https://doi.org/10.3389/fmicb.2020.01598 SN - 1664-302X VL - 11 PB - Frontiers Media CY - Lausanne ER - TY - JOUR A1 - Weithoff, Guntram A1 - Gaedke, Ursula T1 - Mean functional traits of lake phytoplankton reflect seasonal and inter-annual changes in nutrients, climate and herbivory JF - Journal of plankton research N2 - Trait-based approaches have become increasingly successful in community ecology. They assume that the distribution of functional traits within communities responds in a predictable way to alterations in environmental forcing and that strong forcing may accelerate such trait changes. We used high frequency measurements of phytoplankton to test these assumptions. We analyzed the seasonal and long-term dynamics of the community trait mean within a multi-dimensional trait space under alternating multifactorial environmental conditions. The community trait mean exhibited a distinct recurrent annual pattern that reflected minor changes in climate, herbivory and nutrients. Independent of early spring conditions, the community trait mean was repeatedly driven into a narrow confined area in the trait space under pronounced herbivory during the clear water phase. The speed of movement was highest at the onset and the relaxation of such strong unidirectional forcing. Thus, our data support the conceptual framework of trait-based ecology that alterations in environmental conditions are systematically tracked by adjustments in the dominant functional trait values and that the speed of trait changes depends on the kind and intensity of the selection pressure. Our approach provides a sensitive tool to detect small functional differences in the community related to subtle differences in forcing. KW - phytoplankton KW - temporal dynamics KW - climate KW - trait distribution KW - Lake Constance KW - functional traits Y1 - 2017 U6 - https://doi.org/10.1093/plankt/fbw072 SN - 0142-7873 SN - 1464-3774 VL - 39 SP - 509 EP - 517 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Lischke, Betty A1 - Weithoff, Guntram A1 - Wickham, Stephen A. A1 - Attermeyer, Katrin A1 - Großart, Hans-Peter A1 - Scharnweber, Inga Kristin A1 - Hilt, Sabine A1 - Gaedke, Ursula T1 - Large biomass of small feeders: ciliates may dominate herbivory in eutrophic lakes JF - Journal of plankton research N2 - The importance of ciliates as herbivores and in biogeochemical cycles is increasingly recognized. An opportunity to observe the potential consequences of zooplankton dominated by ciliates arose when winter fish kills resulted in strong suppression of crustaceans by young planktivorous fish in two shallow lakes. On an annual average, ciliates made up 38-76% of the total zooplankton biomass in both lakes during two subsequent years. Consequently, ciliate biomass and their estimated grazing potential were extremely high compared with other lakes of various trophic states and depths. Grazing estimates based on abundance and size suggest that ciliates should have cleared the water column of small (<5 mu m) and intermediate (5-50 mu m) sized phytoplankton more than once a day. Especially, small feeders within the ciliates were important, likely exerting a strong top-down control on small phytoplankton. Particle-attached bacteria were presumably strongly suppressed by intermediate-sized ciliate feeders. In contrast to other lakes, large phytoplankton was proportionately very abundant. The phytoplankton community had a high evenness, which may be attributed to the feeding by numerous fast growing and selective ciliate species. Our study highlights ciliates as an important trophic link and adds to the growing awareness of the role of winter processes for plankton dynamics. KW - phytoplankton KW - crustaceans KW - rotifers KW - filtration rate KW - winter fish kill Y1 - 2016 U6 - https://doi.org/10.1093/plankt/fbv102 SN - 0142-7873 SN - 1464-3774 VL - 38 SP - 2 EP - 15 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Brentrup, Jennifer A. A1 - Williamson, Craig E. A1 - Colom-Montero, William A1 - Eckert, Werner A1 - de Eyto, Elvira A1 - Großart, Hans-Peter A1 - Huot, Yannick A1 - Isles, Peter D. F. A1 - Knoll, Lesley B. A1 - Leach, Taylor H. A1 - McBride, Chris G. A1 - Pierson, Don A1 - Pomati, Francesco A1 - Read, Jordan S. A1 - Rose, Kevin C. A1 - Samal, Nihar R. A1 - Staehr, Peter A. A1 - Winslow, Luke A. T1 - The potential of high-frequency profiling to assess vertical and seasonal patterns of phytoplankton dynamics in lakes: an extension of the Plankton Ecology Group (PEG) model JF - Inland waters : journal of the International Society of Limnology N2 - The use of high-frequency sensors on profiling buoys to investigate physical, chemical, and biological processes in lakes is increasing rapidly. Profiling buoys with automated winches and sensors that collect high-frequency chlorophyll fluorescence (ChlF) profiles in 11 lakes in the Global Lake Ecological Observatory Network (GLEON) allowed the study of the vertical and temporal distribution of ChlF, including the formation of subsurface chlorophyll maxima (SSCM). The effectiveness of 3 methods for sampling phytoplankton distributions in lakes, including (1) manual profiles, (2) single-depth buoys, and (3) profiling buoys were assessed. High-frequency ChlF surface data and profiles were compared to predictions from the Plankton Ecology Group (PEG) model. The depth-integrated ChlF dynamics measured by the profiling buoy data revealed a greater complexity that neither conventional sampling nor the generalized PEG model captured. Conventional sampling techniques would have missed SSCM in 7 of 11 study lakes. Although surface-only ChlF data underestimated average water column ChlF, at times by nearly 2-fold in 4 of the lakes, overall there was a remarkable similarity between surface and mean water column data. Contrary to the PEG model’s proposed negligible role for physical control of phytoplankton during the growing season, thermal structure and light availability were closely associated with ChlF seasonal depth distribution. Thus, an extension of the PEG model is proposed, with a new conceptual framework that explicitly includes physical metrics to better predict SSCM formation in lakes and highlight when profiling buoys are especially informative. KW - chlorophyll fluorescence KW - Global Lake Ecological Observatory Network (GLEON) KW - high-frequency sensors KW - PEG model KW - phytoplankton KW - profiling buoys KW - subsurface chlorophyll maximum Y1 - 2016 U6 - https://doi.org/10.5268/IW-6.4.890 SN - 2044-2041 SN - 2044-205X VL - 6 SP - 565 EP - 580 PB - Freshwater Biological Association CY - Ambleside ER - TY - JOUR A1 - Spijkerman, Elly A1 - Stojkovic, Slobodanka A1 - Holland, Daryl A1 - Lachmann, Sabrina C. A1 - Beardall, John T1 - Nutrient induced fluorescence transients (NIFTs) provide a rapid measure of P and C (co-)limitation in a green alga JF - European journal of phycology N2 - Nutrient Induced Fluorescence Transients (NIFTs) have been shown to be a possible way of testing for the limiting nutrient in algal populations. In this study we tested the hypothesis that NIFTs can be used to detect a (co-)limitation for inorganic phosphorus (Pi) and CO2 in the green alga Chlamydomonas acidophila and that the magnitude of the NIFTs can be related to cellular P:C ratios. We show a co-limitation response for Pi and CO2 via traditional nutrient enrichment experiments in natural phytoplankton populations dominated by C. acidophila. We measured NIFT responses after a Pi- or a CO2-spike in C. acidophila batch cultures at various stages of Pi and inorganic C limitation. Significant NIFTs were observed in response to spikes in both nutrients. The NIFT response to a Pi-spike showed a strong negative correlation with cellular P:C ratio that was pronounced below 3 mmol P: mol C (equivalent to 0.2 pg P cell(-1)). Both cellular P and C content influenced the extent of the Pi-NIFT response. The NIFT response to a CO2-spike correlated to low CO2 culturing conditions and also had a negative correlation with cellular P content. A secondary response within the Pi-NIFT response was related to the CO2 concentration and potentially reflected co-limitation. In conclusion, NIFTs provided a quick and reliable method to detect the growth-limiting nutrient in an extremophile green alga, under Pi-, CO2- and Pi/CO2 (co-)limited growth conditions. KW - acidophile KW - Chlamydomonas KW - CO2 concentrating mechanism KW - CO2 limitation KW - extremophile KW - nutrient limitation KW - photosynthesis response KW - phytoplankton KW - stoichiometry Y1 - 2016 U6 - https://doi.org/10.1080/09670262.2015.1095355 SN - 0967-0262 SN - 1469-4433 VL - 51 SP - 47 EP - 58 PB - Hindawi CY - Abingdon ER - TY - JOUR A1 - Wacker, Alexander A1 - Piepho, Maike A1 - Spijkerman, Elly T1 - Photosynthetic and fatty acid acclimation of four phytoplankton species in response to light intensity and phosphorus availability JF - European journal of phycology N2 - Photosynthetic acclimation of phytoplankton to lower irradiation can be met by several strategies such as increasing the affinity for light or increasing antenna size and stacking of the thylakoids. The latter is reflected by a higher proportion of polyunsaturated fatty acids (PUFAs). Additionally, photosynthetic capacity (P-max), respiratory losses, and proton leakage can be reduced under low light. Here we consider the effect of light intensity and phosphorus availability simultaneously on the photosynthetic acclimation and fatty acid composition of four phytoplankters. We studied representatives of the Chlorophyceae, Cryptophyceae and Mediophyceae, all of which are important components of plankton communities in temperate lakes. In our analysis, excluding fatty acid composition, we found different acclimation strategies in the chlorophytes Scenedesmus quadricauda, Chlamydomonas globosa, cryptophyte Cryptomonas ovata and ochrophyte Cyclotella meneghiniana. We observed interactive effects of light and phosphorus conditions on photosynthetic capacity in S. quadricauda and Cry. ovata. Cry. ovata can be characterized as a low light-acclimated species, whereas S. quadricauda and Cyc. meneghiniana can cope best with a combination of high light intensities and low phosphorus supply. Principal component analyses (PCA), including fatty acid composition, showed further species-specific patterns in their regulation of P-max with PUFAs and light. In S. quadricauda and Cyc. meneghiniana, PUFAs negatively affected the relationship between P-max and light. In Chl. globosa, lower light coincided with higher PUFAs and lower P-max, but PCA also indicated that PUFAs had no direct influence on P-max. PUFAs and P-max were unaffected by light in Cry. ovata. We did not observe a general trend in the four species tested and concluded that, in particular, the interactive effects highlight the importance of taking into account more than one environmental factor when assessing photosynthetic acclimation to lower irradiation. KW - chlorophyll content KW - dark respiration KW - FAME KW - light acclimation KW - oxygen evolution KW - photosynthesis KW - phytoplankton KW - polyunsaturated fatty acids Y1 - 2015 U6 - https://doi.org/10.1080/09670262.2015.1050068 SN - 0967-0262 SN - 1469-4433 VL - 50 IS - 3 SP - 288 EP - 300 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Engel, Anja A1 - Piontek, Judith A1 - Grossart, Hans-Peter A1 - Riebesell, Ulf A1 - Schulz, Kai Georg A1 - Sperling, Martin T1 - Impact of CO2 enrichment on organic matter dynamics during nutrient induced coastal phytoplankton blooms JF - Journal of plankton research N2 - A mesocosm experiment was conducted to investigate the impact of rising fCO(2) on the build-up and decline of organic matter during coastal phytoplankton blooms. Five mesocosms (similar to 38 mA(3) each) were deployed in the Baltic Sea during spring (2009) and enriched with CO2 to yield a gradient of 355-862 A mu atm. Mesocosms were nutrient fertilized initially to induce phytoplankton bloom development. Changes in particulate and dissolved organic matter concentrations, including dissolved high-molecular weight (> 1 kDa) combined carbohydrates, dissolved free and combined amino acids as well as transparent exopolymer particles (TEP), were monitored over 21 days together with bacterial abundance, and hydrolytic extracellular enzyme activities. Overall, organic matter followed well-known bloom dynamics in all CO2 treatments alike. At high fCO(2,) higher Delta POC:Delta PON during bloom rise, and higher TEP concentrations during bloom peak, suggested preferential accumulation of carbon-rich components. TEP concentration at bloom peak was significantly related to subsequent sedimentation of particulate organic matter. Bacterial abundance increased during the bloom and was highest at high fCO(2). We conclude that increasing fCO(2) supports production and exudation of carbon-rich components, enhancing particle aggregation and settling, but also providing substrate and attachment sites for bacteria. More labile organic carbon and higher bacterial abundance can increase rates of oxygen consumption and may intensify the already high risk of oxygen depletion in coastal seas in the future. KW - mesocosm KW - ocean acidification KW - phytoplankton KW - organic matter KW - TEP Y1 - 2014 U6 - https://doi.org/10.1093/plankt/fbt125 SN - 0142-7873 SN - 1464-3774 VL - 36 IS - 3 SP - 641 EP - 657 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Rocha, Marcia R. A1 - Gaedke, Ursula A1 - Vasseur, David A. T1 - Functionally similar species have similar dynamics JF - The journal of ecology N2 - 1. Improving the mechanistic basis of biodiversity-ecosystem function relationships requires a better understanding of how functional traits drive the dynamics of populations. For example, environmental disturbances or grazing may increase synchronization of functionally similar species, whereas functionally different species may show independent dynamics, because of different responses to the environment. Competition for resources, on the other hand, may yield a wide range of dynamic patterns among competitors and lead functionally similar and different species to display synchronized to compensatory dynamics. The mixed effect of these forces will influence the temporal fluctuations of populations and, thus, the variability of aggregate community properties. 2. To search for a relationship between functional and dynamics similarity, we studied the relationship between functional trait similarity and temporal dynamics similarity for 36 morphotypes of phytoplankton using long-term high-frequency measurements. 3. Our results show that functionally similar morphotypes exhibit dynamics that are more synchronized than those of functionally dissimilar ones. Functionally dissimilar morphotypes predominantly display independent temporal dynamics. This pattern is especially strong when short time-scales are considered. 4. Negative correlations are present among both functionally similar and dissimilar phytoplankton morphotypes, but are rarer and weaker than positive ones over all temporal scales. 5. Synthesis. We demonstrate that diversity in functional traits decreases community variability and ecosystem-level properties by decoupling the dynamics of individual morphotypes. KW - compensatory dynamics KW - competition KW - environmental forcing KW - functional diversity KW - functional traits KW - grazing KW - phytoplankton KW - plant population and community dynamics KW - synchrony KW - temporal dynamics Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2745.2011.01893.x SN - 0022-0477 VL - 99 IS - 6 SP - 1453 EP - 1459 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Wacker, Alexander A1 - Martin-Creuzburg, Dominik T1 - Biochemical nutrient requirements of the rotifer Brachionus calyciflorus co-limitation by sterols and amino acids JF - Functional ecology : an official journal of the British Ecological Society N2 - It has been proposed that growth and reproduction of animals is frequently limited by multiple nutrients simultaneously. To improve our understanding of the consequences of multiple nutrient limitations (i.e. co-limitation) for the performance of animals, we conducted standardized population growth experiments using an important aquatic consumer, the rotifer Brachionus calyciflorus. We compared nutrient profiles (sterols, fatty acids and amino acids) of rotifers and their diets to reveal consumerdiet imbalances and thus potentially limiting nutrients. In concomitant growth experiments, we directly supplemented potentially limiting substances (sterols, fatty acids, amino acids) to a nutrient-deficient diet, the cyanobacterium Synechococcus elongatus, and recorded population growth rates. The results from the supplementation experiments corroborated the nutrient limitations predicted by assessing consumerdiet imbalances, but provided more detailed information on co-limiting nutrients. While the fatty acid deficiency of the cyanobacterium appeared to be of minor importance, the addition of both cholesterol and certain amino acids (leucine and isoleucine) improved population growth rates of rotifers, indicating a simultaneous limitation by sterols and amino acids. Our results add to growing evidence that consumers frequently face multiple nutrient limitations and suggest that the concept of co-limitation has to be considered in studies assessing nutrient-limited growth responses of consumers. KW - consumer KW - consumer-diet imbalance KW - dietary mismatch KW - fatty acid KW - global change KW - lipid KW - nutrition KW - phytoplankton KW - tetrahymanol KW - zooplankton Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2435.2012.02047.x SN - 0269-8463 VL - 26 IS - 5 SP - 1135 EP - 1143 PB - Wiley-Blackwell CY - Hoboken ER - TY - THES A1 - Fiedler, Dorothea T1 - Impact of Dissolved Organic Nitrogen on Freshwater Phytoplankton N2 - In freshwater sciences, nitrogen gained increasing attention in the past as an important resource potentially influencing phytoplankton growth and thus eutrophication. Most studies and all management approaches, however, are still restricted to dissolved inorganic nitrogen (DIN = nitrate + nitrite + ammonium) since dissolved organic nitrogen (DON) was considered to be refractory for most of the photoautotrophs. In the meantime this assumption has been disproved for all aquatic systems. While research on DON in marine ecosystems substantially increased, in freshwater a surprisingly small number of investigations has been carried out on DON utilization by phytoplankton or even the occurrence and seasonal development of total DON or its compounds in lakes. Therefore, our present knowledge on DON utilization by phytoplankton is often based on single species experiments using a sole, usually low molecular weight DON component, often in unnaturally high amounts mainly carried out with marine phytoplankton species. Thus, we know that some phytoplankton species can take up different DON fractions if they are available in high concentrations and as sole nitrogen source. This does not necessarily imply that phytoplankton would perform likewise in natural environments. In addition, it will be difficult to draw conclusions on the behavior of freshwater phytoplankton from experiments with marine phytoplankton since the nutrient regime in marine environments differs from that of freshwater. In the light of the parallel availability of inorganic and organic nitrogen species in natural freshwater ecosystems, several questions must be raised: "If inorganic nitrogen is available, would phytoplankton really rely on an organic nitrogen source? Could a connection be detected between the seasonal development of DON and changes in the phytoplankton community composition as found for inorganic nitrogen? And if we reduce the input of inorganic nitrogen in lakes and rivers would the importance of DON as nitrogen source for phytoplankton increase, counteracting all management efforts or even leading to undesired effects due to changes in phytoplankton physiology and biodiversity?" I experimentally addressed the questions whether those DON compounds differentially influence growth, physiology and composition of phytoplankton both as sole available nitrogen source and in combination with other nitrogen compounds. I hypothesized that all offered DON - compounds (urea, natural organic matter (NOM), dissolved free and combined amino acids (DFAA, DCAA)) could be utilized by phytoplankton at natural concentrations. However, I assumed that the availability would decrease with increasing compound complexity. I furthermore hypothesized that the occurrence of low DIN concentrations would not affect the utilization of DON negatively. The nitrogen source, whatsoever, would have an impact on phytoplankton physiology as well as community composition. To investigate these questions and assumptions I conducted bioassays with algae monocultures as well as phytoplankton communities testing the utilization of various DON compounds by several freshwater phytoplankton species. Especially the potential utilization of NOM, a complex DON compound mainly consisting of humic substances is of interest, since it is usually regarded to be refractory. In order to be able to use natural concentrations of DON - compounds for my experiments the concentration of total DON and some DON - compounds (urea, humic substances, heigh molecular weight substances) was assessed in Lake Müggelsee. All compounds were able to support algae growth in the low natural concentrations supplied. However, I found that the offered DON compounds differ in their availability to various algae species, both, as sole nitrogen source or in combination with low DIN concentrations. As expected, the availability decreased with increasing complexity of the nitrogen compound. Furthermore, I could show that changes in algal physiology (nitrogen storage, metabolism) occur depending on the utilized nitrogen source. Especially the secondary photosynthetic pigment composition, heterocyst frequency and C:N - ratio of the algae were affected. The uptake and usage of certain nitrogen compounds might be more costly, potentially resulting in those physiology changes. Whereas laboratory experiments with single species revealed strong effects of DON, algal responses to DON in a multi-species situation remain unclear. Experiments with phytoplankton communities from Lake Müggelsee revealed that the nitrogen pool composition does influence the phytoplankton community structure. The findings furthermore show that several species combined might utilize the supplied nitrogen completely different than monocultures in the laboratory. Thus, besides the actual ability of algae to use the offered nitrogen sources other factors, such as interspecific competition, may be of importance. I further investigated, if the results of the laboratory experiments, can be verified in the field. Here, I surveyed the seasonal development of several dissolved organic matter (DOM) components (urea, high molecular weight substances (HMWS), humic substances (HS)) and associated parameters (Specific UV-absorption (SUVA), C:N - ratio) in Lake Müggelsee between 2011 and 2013. Furthermore, data from the long term measurements series of Lake Müggelsee such as physical (temperature, light, pH, O2) and chemical parameters (nitrogen, phosphorous, silica, inorganic carbon), zooplankton and phytoplankton data were used to investigate how much of the variability of the phytoplankton composition in Lake Müggelsee can be explained by DON/DOM concentration and composition, relative to the other groups of explanatory variables. The results show that DON mainly consists of rather complex compounds such as humic substances and biopolymers (80 %) and that only slight seasonal trends are detectable. Using variance partitioning I could show, that the usually investigated nutrients (DIN, silica, inorganic carbon, phosphorous) and abiotic factors together explain most of the algae composition as was to be expected (57.1 % of modeled variance). However, DOM and the associated parameters uniquely explain 10.3 % of the variance and thus slightly more than zooplankton with 9.3 %. I could therefore prove, that the composition of DOM (nitrogen and carbon) is connected to the algae composition in an eutrophic lake such as Lake Müggelsee. DON - compounds such as urea, however, could not be correlated with the occurrence of specific phytoplankton species. Overall, the results of this study imply that DON can be a valuable nitrogen source for freshwater phytoplankton. DON is used by various species even when DIN is available in low concentrations. Through the reduction of DIN in lakes and rivers, the DON:DIN ratio might be changed, resulting even in an increased importance of DON as phytoplankton nitrogen source. My work suggests that not only N2-fixation but also DON utilization might compensate for reduced N - input. Changes from DIN to DON as main nitrogen source might also promote certain, potentially undesired algae species and influence the biodiversity of a limnic ecosystem through changes in the phytoplankton community structure. Thus, DON, especially urea, should be included in calculations concerning total available nitrogen and when determining nitrogen threshold values. Furthermore, the input-reduction of DON, for example from waste-water treatment plants should also be evaluated and the results of my thesis should find consideration when planning to reduce the nitrogen input in freshwater. N2 - Das Interesse an Stickstoff als potentielle Einflußgröße auf das Phytoplanktonwachstum und damit auch als Eutrophierungsfaktor hat in der Vergangenheit in der Limnologie stark zugenommen. Bisher ging man davon aus, das gelöster organischer Stickstoff (DON) für photoautotrophe Organismen refraktär, also nicht nutzbar ist. Dies führte dazu, dass der Großteil an Studien und Managementmaÿnahmen nur gelösten inorganischen Stickstoff (DIN = Nitrat + Nitrit + Ammonium) einbezieht. Mittlerweile wurde allerdings für alle aquatischen Systeme nachgewiesen, dass DON durchaus für Organismen verfügbar sein kann. Während die Forschung im marinen Bereich stark zugenommen hat, wurden in Binnengewässern nur sehr wenige Untersuchungen zur DON - Nutzung durch Phytoplankton oder auch nur das Vorkommen und die saisonale Entwicklung von DON oder seiner Komponenten durchgeführt. Dies resultiert darin, dass sich unser heutiges Wissen zur DON - Nutzung durch Pytoplankton hauptsächlich auf Experimente stützt, die mit einzelnen, überwiegend marinen Phytoplanktonarten und einer, üblicherweise niedermolekularen DON - Komponente in meist unnatürlich hohen Konzentrationen durchgeführt wurden. Demzufolge wissen wir nur, dass es einige Phytoplanktonarten gibt, die verschiedene DON - Fraktionen aufnehmen können, wenn sie in hohen Konzentrationen und als alleinige Stickstoffquelle vorliegen. Diese Ergebnisse spiegeln nicht das tatsächliche Verhalten von Phytoplankton in seiner natürlichen Umgebung wieder. Zudem ist es schwierig, von Experimenten mit marinen Phytoplanktonarten auf das Verhalten limnischer Phytoplankter zu schließen, da sich der Nährstoffhaushalt in marinen Systemen von dem in Binnengewässern stark unterscheidet. Im Hinblick auf die parallele Verfügbarkeit von inorganischem und organischem Stickstoff in natürlichen Binnengewässern stellen sich eine Vielzahl von Fragen: "Wie stark DON als Stickstoffquelle durch Phytoplankton genutzt wird, wenn auch inorganischer Stickstoff zur Verfügung steht. Gibt es eventuell eine Verbindung zwischen der saisonalen Entwicklung von DON und Änderungen in der Zusammensetzung der Phytoplanktongemeinschaft wie man es auch für inorganischen Stickstoff sowie andere biotische und abiotische Faktoren findet? Es ist bisher auch ungeklärt, ob durch eine Reduktion des Eintrags von inorganischem Stickstoff die Bedeutung von DON als Stickstoffquelle für Phytoplankton zunimmt. Würde so eventuell den Managmentmaßnahmen entgegengewirkt oder käme es zu ungewünschten Effekten durch Änderungen in Phytoplanktonphysiologie und Biodiversität?" Im Verlauf meiner Doktorarbeit habe ich mich mit einem Teil dieser offenen Fragen auseinandergesetzt. Meine Experimente dienten dazu herauszufinden, inwieweit sich verschiedene DON -Komponenten auf Wachstum, Physiologie und die Phytoplanktonzusammensetzung auswirken, wenn sie als einzige verfügbare Stickstoffquelle aber auch in Kombination mit anderen Stickstoffkomponenten zur Verfügung stehen. Hierbei stehen folgende Hypothesen und Annahmen im Vordergrund: a) alle angebotenen DON - Komponenten (Harnstoff, gelöste freie Aminosäuren (DFAA), gelöste gebundene Aminosäuren (DCAA) und natürliches organisches Material (NOM)) können in natürlicher Konzentration von Phytoplankton genutzt werden, b) die Verfügbarkeit nimmt mit zunehmender Komplexität des DON ab, c) geringe DIN - Konzentrationen haben keinen negativen Einfluss auf die Nutzung von DON durch das Phytoplankton, d) die Stickstoffquelle beeinflusst Phytoplanktonphysiologie sowie die Zusammensetzung der Phytoplanktongemeinschaft. Um mehr Informationen zur DON - Verfügbarkeit für Süßwasserphytoplankton zu erhalten, wurde zunächst die Nutzung verschiedener DON - Komponenten durch verschiedene Phytoplanktonspezies aus Binnengewässern sowie Phytoplanktongemeinschaften untersucht. Besonders die mögliche Nutzung von NOM, einer komplexen, hauptsächlich aus Huminstoffen bestehenden DON - Komponente war von Interesse, da sie überwiegend als refraktär eingeschätzt wird. Um die Verfügbarkeit diverser DON - Komponenten in natürlicher Konzentration zu testen, wurde zunächst die Konzentration von Gesamt - DON sowie einiger DON -Komponenten (Harnstoff, Huminstoffe, hochmolekulare Substanzen) im Müggelsee ermittelt. Alle DON - Komponenten ermöglichten ein Algenwachstum in der niedrigen natürlichen Konzentration, in der sie zur Verfügung gestellt wurden. Es konnte festgestellt werden, dass sich die unterschiedlichen DON - Komponenten in ihrer Verfügbarkeit für verschiedene Algenarten unterschieden, unabhängig davon, ob sie als alleinige Stickstoffquelle vorlagen oder in Kombination mit DIN in niedriger Konzentration. Wie erwartet nahm die Algenverfügbarkeit mit zunehmender Komplexität der Stickstoffkomponenten ab. Desweiteren konnte gezeigt werden, dass die verwendete Stickstoffquelle zu Änderungen in der Algenphysiologie (Metabolismus, Stickstoffspeicherung) führen kann. Vor allem die Zusammensetzung sekundärer Photosynthesepigmente, die Heterocystenhäufigkeit sowie das C:N - Verhältnis des Phytoplankton wurden beeinflusst. Auch wenn alle untersuchten Stickstoffquellen das Phytoplanktonwachstum ermöglichen, ist die Nutzung einiger Komponenten gegebenenfalls mit höheren Kosten z.B. für Transport, Aufschluß etc. verbunden, was wiederum in einer Änderungen der Phytoplanktonphysiologie resultieren kann. Während Experimente mit einzelnen Phytoplanktonarten im Labor starke Effekte von DON erkennen lassen, sind die Ergebnisse der Multi-Spezies-Versuche weniger eindeutig interpretierbar. Versuche mit Phytoplanktongemeinschaften aus dem Müggelsee zeigten, dass die Zusammensetzung des Stickstoffpools Auswirkungen auf die Struktur der Phytoplanktongemenschaft hat. Zudem nutzen verschiedene Arten zusammen den zur Verfügung gestellten Stickstoff anders, als Monokulturen im Labor. Demzufolge spielen neben der eigentlichen Fähigkeit der Algen, verschiedene Stickstoffkomponenten nutzen zu können noch andere Faktoren wie z.B. interspezifische Konkurrenz eine Rolle für die tatsächliche Nutzung im Gewässer. Im weiteren Teil meiner Doktorarbeit habe ich untersucht, inwieweit die Ergebnisse der Laborversuche im Feld verifiziert werden können. Dafür wurde die saisonale Entwicklung verschiedenen gelösten organischen Materials (DOM) (Harnstoff, hochmolekulare Substanzen (HMWS), Huminstoffe (HS)) und weitere assoziierte Parameter (spezifische UV-Absorption (SUVA), C:N - Verhältnis) im Müggelsee von 2011-2013 bestimmt. Desweiteren wurden Daten aus der Langzeitmessung vom Müggelsee verwendet, um herauszufinden, wieviel der Variabilität in der Phytoplanktonzusammensetzung im Müggelsee durch die DON / DOM Konzentration und Zusammensetzung erklärt werden, im Verhältnis zu den anderen potentiellen Einflussfaktoren. Hierzu zählen physikalische (Temperatur, Licht, pH, O2) und chemische Parameter (Stickstoff, Phosphor, Silikat, inorganischer Kohlenstoff), Zooplankton- und Phytoplanktondaten. Die Ergebnisse zeigen, dass sich DON hauptächlich aus komplexen Komponenten wie Huminstoffen und Biopolymeren (80 %) zusammensetzt und das nur ein geringer saisonaler Trend in der DON-Entwicklung festzustellen ist. Mittels Varianzpartitionierung konnte gezeigt werden, dass die üblicherweise untersuchten Nährstoffe (DIN, Silikat, inorganischer Kohlenstoff, Phosphor) und abiotische Faktoren zusammen den Großteil der Algenzusammensetzung erklären, wie zu erwarten war (57.1 %). DOM und die damit assoziierten Parameter konnten allein 10.3% der Varianz erklären und damit etwas mehr als Zooplankton, eine anerkannte Einflußgröße, mit 9.3%. Damit konnte gezeigt werden, dass auch die DOM - Zusammensetzung (Stickstoff und Kohlenstoff) als Einflussgröße der Algenzusammensetzung in einem eutrophen See wie dem Müggelsee berücksichtigt werden sollte. Zusammenfassend zeigen die Ergebnisse dieser Doktorarbeit, dass DON eine wichtige Stickstoffquelle für Phytoplankton aus Binnengewässern sein kann und von zahlreichen Arten genutzt wird, auch wenn DIN, zumindest in niedrigen Konzentrationen, verfügbar ist. Durch die Reduktion von DIN in Seen und Flüssen könnte es zu einer Änderung des DON / DIN - Verhältnisses kommen, was zu einer noch stärkeren Bedeutung von DON als Stickstoffquelle für Phytoplankton führen kann. Meine Arbeit legt nahe, dass nicht nur die N2 - Fixierung, sondern auch die Nutzung von DON eine Reduktion des Stickstoffeintrags kompensieren könnte. Ein Wechsel von DIN zu DON als Hauptstickstoffquelle für Phytoplankton fördert möglicherweise auch bestimmte unerwünschte Algenarten und beeinflusst die Biodiversität der Binnengewässer durch Änderungen in der Phytoplanktongemeinschaft. Aus diesen Gründen sollte DON, vor allem Harnstoff in Kalkulationen des gesamtverfögbaren Stickstoffs sowie bei der Ermittlung von Stickstoffgrenzwerten einbezogen werden. Bei der Planung von Maßnahmen zur Reduktion des Stickstoffeintrages in Binnengewässer zur Verbesserung der Wasserqualtät sollten die Ergebnisse dieser Doktorarbeit demzufolge in Betracht gezogen und auch eine Reduktion des DON - Eintrages, z. B. aus Klärwerken, erwogen werden. KW - DON KW - phytoplankton KW - natural organic matter KW - LC-OCD-OND Y1 - 2016 ER - TY - THES A1 - Huber, Veronika Emilie Charlotte T1 - Climate impact on phytoplankton blooms in shallow lakes T1 - Der Einfluss des Klimas auf Algenblüten in Flachseen N2 - Lake ecosystems across the globe have responded to climate warming of recent decades. However, correctly attributing observed changes to altered climatic conditions is complicated by multiple anthropogenic influences on lakes. This thesis contributes to a better understanding of climate impacts on freshwater phytoplankton, which forms the basis of the food chain and decisively influences water quality. The analyses were, for the most part, based on a long-term data set of physical, chemical and biological variables of a shallow, polymictic lake in north-eastern Germany (Müggelsee), which was subject to a simultaneous change in climate and trophic state during the past three decades. Data analysis included constructing a dynamic simulation model, implementing a genetic algorithm to parameterize models, and applying statistical techniques of classification tree and time-series analysis. Model results indicated that climatic factors and trophic state interactively determine the timing of the phytoplankton spring bloom (phenology) in shallow lakes. Under equally mild spring conditions, the phytoplankton spring bloom collapsed earlier under high than under low nutrient availability, due to a switch from a bottom-up driven to a top-down driven collapse. A novel approach to model phenology proved useful to assess the timings of population peaks in an artificially forced zooplankton-phytoplankton system. Mimicking climate warming by lengthening the growing period advanced algal blooms and consequently also peaks in zooplankton abundance. Investigating the reasons for the contrasting development of cyanobacteria during two recent summer heat wave events revealed that anomalously hot weather did not always, as often hypothesized, promote cyanobacteria in the nutrient-rich lake studied. The seasonal timing and duration of heat waves determined whether critical thresholds of thermal stratification, decisive for cyanobacterial bloom formation, were crossed. In addition, the temporal patterns of heat wave events influenced the summer abundance of some zooplankton species, which as predators may serve as a buffer by suppressing phytoplankton bloom formation. This thesis adds to the growing body of evidence that lake ecosystems have strongly responded to climatic changes of recent decades. It reaches beyond many previous studies of climate impacts on lakes by focusing on underlying mechanisms and explicitly considering multiple environmental changes. Key findings show that climate impacts are more severe in nutrient-rich than in nutrient-poor lakes. Hence, to develop lake management plans for the future, limnologists need to seek a comprehensive, mechanistic understanding of overlapping effects of the multi-faceted human footprint on aquatic ecosystems. N2 - Weltweit haben Seeökosysteme auf den Klimawandel der letzten Jahrzehnte reagiert. Beobachtete Veränderungen eindeutig dem Klimawandel zuzuordnen, wird jedoch häufig dadurch erschwert, dass Seen gleichzeitig vielfachen anthropogenen Einflüssen ausgesetzt sind. Diese Arbeit trägt zu einem besseren Verständnis des Klimaeinflusses auf Algen bei, die am Anfang der Nahrungskette stehen und maßgeblich die Wasserqualität eines Sees beeinflussen können. Zum größten Teil stützt sich die Arbeit auf eine dreißigjährige Datenreihe eines unregelmäßig geschichteten Flachsees im Nordosten von Deutschland (Müggelsee), in dem sowohl steigende Wassertemperaturen als auch sinkende Nährstoffeinträge zu verzeichnen waren. Bei der Datenanalyse wurde ein neu erstelltes dynamisches Simulationsmodell, genetische Algorithmen zur Parametrisierung von Modellen, und statistische Methoden der Klassifizierung und Zeitreihenanalyse genutzt. Ergebnisse dieser Arbeit zeigen, dass nicht nur klimatische Faktoren sondern auch die Nährstoffverfügbarkeit im See den Zeitpunkt der Algenfrühjahrsblüte (Phänologie) beeinflussen. Durch eine Veränderung der Mechanismen, die zum Kollaps der Blüte führen, trat diese trotz ähnlich milder Winterbedingungen bei hoher Nährstoffverfügbarkeit früher auf als bei niedriger. Ein neuentwickelter Ansatz zur Modellierung von Phänologie erwies sich als geeignet, um vorherzusagen, wann Algen und ihre Räuber in einem künstlich periodisch angetriebenen Laborsystem ihre Populationshöhepunkte erreichten. Eine Verlängerung der Wachstumsperiode führte dazu, dass diese früher auftraten. Die Untersuchung, warum sich Blaualgen im betrachteten See während jüngster Hitzewellenereignisse überraschend unterschiedlich entwickelt hatten, ergab, dass ungewöhnlich warmes Wetter nicht wie häufig vermutet generell förderlich für ihre Entwicklung ist. Der Zeitpunkt und die Dauer der Hitzewellen waren entscheidend dafür, ob für Blaualgen kritische Schwellenwerte der thermischen Schichtung im See überschritten wurden. Zudem zeigte sich, dass saisonale Erwärmungsmuster einen bedeutenden Einfluss auf Räuber nahmen, die das Auftreten von Algenblüten verhindern können. Diese Arbeit reiht sich in eine wachsende Anzahl von Studien ein, die zeigen, dass Seeökosysteme bereits stark auf die Klimaveränderungen der letzen Jahrzehnte reagiert haben. Mit ihrem Fokus auf Mechanismen und der expliziten Berücksichtigung simultaner anthropogener Einflüsse geht diese Arbeit gleichzeitig über viele bisherige Studien hinaus, die sich auf reine Beobachtung und die Betrachtung klimatischer Faktoren beschränkten. Kernergebnisse deuten daraufhin, dass Klimafolgen in nährstoffreichen Seen stärker ausfallen als in nährstoffarmen Seen. Nur mit einem umfassenden, mechanistischen Verständnis des vielfältigen anthropogenen Einflusses wird eine hohe Wasserqualität in Seen auch in Zukunft aufrechtzuerhalten sein. KW - Klimawandel KW - Gewässer KW - Phytoplankton KW - Phänologie KW - Modellierung KW - climate change KW - freshwater KW - phytoplankton KW - phenology KW - modelling Y1 - 2010 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-42346 ER -