Charophyte Species Research Articles

Charophytes collapse beyond a critical warming and brownification threshold in shallow lake systems

Charophytes play a critical role for the functioning of shallow lake ecosystems. Although growth of charophytes can be limited by many factors, such as temperature, nutrients and light availability, our understanding about concomitant effects of climate warming and other large-scale environmental perturbations, e.g. increases in humic matter content (‘brownification’) is still limited. Here we conducted an outdoor mesocosm experiment during 71days with a common charophyte species, Chara vulgaris, along an increasing gradient of temperature and brownification. We hypothesized the growth of C. vulgaris to increase with temperature, but to level off along the combined temperature and brownification gradient when reaching a critical threshold for light limitation via brownification. We show that C. vulgaris increases the relative growth rate (RGR), main and total shoot elongation, as well as number of lateral shoots when temperature and brownification increased by +2°C and+100%, respectively above today's levels. However, the RGR, shoot elongation and number of lateral shoots declined at further increment of temperature and brownification. Macrophyte weight-length ratio decreased with increased temperature and brownification, indicating that C. vulgaris allocate more resources or energy for shoot elongation instead of biomass increase at warmer temperatures and higher brownification. Our study shows that C. vulgaris will initially benefit from warming and brownification but will then decline as a future scenario of increased warming and brownification reaches a certain threshold level, in case of our experiment at +4°C and a 2-fold increase in brownification above today's levels.

Genetic variability of charophyte algae in the Baltic Sea area

Abstract The Baltic Sea, a young habitat in geological terms, is characterised by strong climatic and salinity gradients that determine species distribution and trigger adaptation processes. The aim here was to test the hypothesis that Baltic Sea charophytes which originate from large freshwater populations exhibit a higher genetic variability than euryhaline charophyte species, restricted to a small number of brackish-marine populations. For this, genetic variability of euryhaline, mesohaline and halotolerant freshwater charophytes with different distribution patterns and population sizes were analysed. Euryhaline Lamprothamnium papulosum, restricted to a few and small populations in the Baltic Sea, showed a complete lack of genetic variability. Also euryhaline Tolypella with large and widely distributed populations displayed only low genetic variability. On the other hand, mesohaline Chara canescens, one of the most common charophytes in the Baltic Sea, exhibited comparatively high genetic variability, in spite of its parthenogenetic mode of reproduction. Halotolerant Chara baltica, originating from freshwater ancestors with a huge number of populations all over Europe, showed a rather restricted genetic variability, indicating a habitat filter acting prior to colonisation of brackish habitats.

New interesting records of charophytes (Charales, Charophyceae) from Eurasia and Africa

A revision of specimens from selected herbaria allowed extension (or confirmation) of the geographical distribution of five charophyte species. Chara globata is a new record for Africa (Tunisia), R...

The occurrence of sexualChara canescens(Charales, Charophyceae) in Sardinia (Italy)

ABSTRACTChara canescens Loisel. is the only haplostichous charophyte species in Europe. Populations with parthenogenetically reproducing females have been described from several European locations....

Six Taxa of Newly Recorded Species of Charophytes (Charophyta) in Korea

Six taxa of unrecorded Korean species of charophytes are described. Freshwater and aerial charophytes were collected from the bark of trees, reservoirs, small ponds and swamps from April 2017 to September 2017. The newly recorded species of Korea were Cosmarium quadrifarium f. octastichum, Euastrum turneri, Spondylosium nitens var. triangulare, Staurastrum kouwetsii, Staurodesmus dickiei var. latus, and Klebsormidium subtile. K. subtile was transferred from Stichococcus subtilis.

The seasonal effects on the encrustation of charophytes in two hard-water lakes.

Encrustation and element content of six charophyte species from two hard-water lakes were investigated monthly for a period of 1year. Seasonal patterns were analyzed for the interaction of water chemistry. Encrustation followed a seasonal pattern for Chara contraria, Chara subspinosa, and Nitellopsis obtusa in Lake Krüselin and for Chara globularis and Chara tomentosa in Lake Lützlow. However, no seasonality in the precipitated CaCO3 was observed for C.subspinosa in Lake Lützlow and for C.tomentosa in Lake Krüselin, indicating a lake-specific dependency. Species-specific encrustation was found. Chara contraria and N.obtusa encrusted the most in June and August, whereas C.subspinosa and Nitella flexilis/opaca exhibited lowest encrustation in March and April. The precipitated CaCO3 of charophytes correlated negatively to the concentration of total inorganic carbon in both lakes. Element content of plant dry weight was species-specific for Ca and K, and lake-specific for Mg. No specific pattern was found for the TP and Fe contents. The results showed seasonal, species, and lake-specific influences on the encrustation of charophytes.

Encrustations and element composition of charophytes from fresh or brackish water sites – habitat- or species-specific differences?

Comparison of encrustation and analysis of element contents across species growing in freshwater (FW) and brackish water (BW) have never been done. Proportion of carbonate and element composition for Ca, K, Mg, Na, and P of plant DW were investigated in four charophyte species from ten freshwater and six brackish water sites in northern Europe. Chara aspera and C. tomentosa were found in both FW and BW sites, whereas C. subspinosa and Nitellopsis obtusa occurred in freshwater only. Significant differences in encrustation were found between FW and BW sites. Individuals from FW had a far higher carbonate content based on dry weight than individuals from BW. In BW, C. tomentosa was less encrusted than C. aspera. This might be explained by the osmoregulation capacities of the brackish water species. The K/Na ratio differed between FW and BW in a species-specific manner. Element composition was habitat-specific for Ca and Mg, species-specific for K, and habitat- and species-specific for Na. P contents showed no specific pattern.

Persistence of submerged macrophytes in a drying world: Unravelling the timing and the environmental drivers to produce drought‐resistant propagules

Abstract Under a warming scenario many permanent inland water bodies in the Mediterranean region have become temporary ones, so the persistence of submerged macrophytes depends on the timely production of drought‐resistant propagules. Phenological research measures the timing of ecological processes and allows the consequences of disturbances such as climate change to be evaluated. Among macrophytes, the charophytes are widely distributed benthic macroalgae and are particularly sensitive to environmental variations. The systems in which they live constitute valuable, threatened, and protected habitats (European Habitats Directive code 3140). This study established a methodological basis for determining which environmental drivers trigger the sexual reproductive phenology of charophytes. For the first time, circular statistics were applied to describe and compare seasonal patterns for submerged macrophytes. Over a period of 2 years, three charophyte species growing in two Mediterranean brackish ponds were monitored. Most of the sexual reproduction occurred during spring and summer, including the production of drought‐resistant propagules, before the harshest conditions arrived. Each species showed a distinctive phenological pattern, according to specific breeding systems, life cycles, and environmental tolerances and requirements. Deeper conditions and higher salinities delayed reproduction. Different rainfall intensities in autumn produced distinctions between years, as stronger rainfall reduced the salinity stress and stimulated the reproduction of plants. Interacting factors act as cues for charophyte reproduction and cause antagonistic effects on propagule production. Among them, the heat required for each phenophase peak is essential for understanding the phenology of a population and for predicting its long‐term persistence. Charophytes appear to be good candidates for tracking climate change in shallow ecosystems. Further phenological studies should consider more species, populations, and long‐term observations in order to predict climate‐change effects on water bodies, and to develop effective plans for management and conservation. Circular statistics is a potential tool for analysing phenology in the context of global warming, as well as for many other conservation issues.

How much can the occurrence and coverage of charophytes in an estuarine lagoon (Curonian Lagoon) be explained by environmental factors?

Aquatic macrophytes play an important role in the structure and functioning of lagoon ecosystems. We assessed the importance of biotic and abiotic environmental factors in controlling spatial patterns of charophyte occurrence and coverage in the Curonian Lagoon. The relationships among five charophyte species, abiotic and biotic environmental factors were assessed using canonical correspondence analysis and multivariate regression trees. Salinity and wave exposure were the most important environmental factors explaining the occurrence and coverage of charophytes species in the estuarine part of the lagoon. The salinity gradient restricted the occurrence of brackish water species (especially Chara baltica and Tolypella nidifica) and freshwater species (especially Nitellopsis obtusa). The occurrence and coverage of C. contraria and T. nidifica were positively associated with the wave exposure and related factors (the bottom slope and grain size of sediments). The cover of N. obtusa could be suppressed by shading and/or space limitation by dense stands of Potamogeton perfoliatus. Relatively low explained variation in the occurrence and coverage (respectively, 28 and 19%) of charophytes by environmental factors highlights the need for analysis of other important factors (e. g. chemical content of sediments, dynamics of propagule bank and herbivory), and better resolution in linking macrophyte community composition with environmental data.

Oxygen stable isotope composition of carbonate encrustations of two modern, widely distributed, morphologically different charophyte species

Oxygen (δ18O) and carbon (δ13C) stable isotope analyses are among the standard methods applied in the studies of past environment, including climate. In lacustrine sediments, δ18O and δ13C values can be measured in various carbonates including charophyte encrustations. Application of the stable isotope record of lacustrine carbonates requires knowledge about the possibilities and limitations of the method. Thus, this study presents the oxygen stable isotope composition of carbonate encrustations precipitated by modern charophytes (δ18OCARB) and of ambient waters (δ18OWATER). The study objects were widely distributed and morphologically different charophyte species, large and branchy Chara tomentosa L. and small and slender Chara globularis Thuill. Each species was studied in five lakes located in western Poland, at three sites per lake. The study demonstrated that δ18OCARB values were similar for the two charophyte species and were lake-dependent. δ18OCARB and δ18OWATER relationships were also similar for the studied charophytes with carbonate encrustations 18O-depleted compared to ambient waters. The shift of mean δ18O values between C. tomentosa and C. globularis encrustations and ambient waters, 2‰ and 3.2‰, respectively, was evidenced in all studied lakes which may indicate potential applicability of δ18OCARB of the two species in paleolimnological studies.

Taphonomy and palaeoecology in the upper Barremian of the SW Iberian chain (Spain): A model to compare taxonomy and diversity of biotas from different coeval basins

A detailed study of the floral and faunal diversity of an upper Barremian lentic ecosystem was performed by examining 50,000microfossils. The study provides an assemblage of 41 species of charophytes, spermatophytes, ostracods, molluscs, and vertebrates (including eggshells). The main goal of this study is to reconstruct the palaeoecology of a fluvio-lacustrine and associated carbonate depositional system, by integrating the sedimentology, taphonomy, and diversity from twelve horizons cropping out in the Buenache de la Sierra and the Las Hoyas basins. The studied area corresponds to the lowermost succession of the Tragacete Formation (Serranía de Cuenca, Iberian chain). Four facies associations (polymictic alluvial; carbonate palustrine and lacustrine; eutrophic lacustrine; and calcarenitic drainage facies) were correlated to the composition of the fossil assemblages, which have yielded a set of taphofacies confirmed by the non-metric multidimensional scaling ordination test of all the horizons. The taphofacies are: (α) dominated by bones and plant leaves, (β) by charophytes-ostracods-bivalves and eggshells, and (γ) by coal-leaves and bones. The Tragacete depositional system consists of demic and mostly autochthonous (non-catastrophic) fossil associations. A mixture of aquatic and terrestrial plants, freshwater molluscs and ostracods coupled with aquatic and terrestrial vertebrate species fosters a biodiversity typical of depositional environments that are congruent with modern floodplain wetland systems. These floodplain wetlands are characterised by a combination of periodically inundated ponds, small lakes, and floodplain areas with terrestrial habitats. As such, they provide suitable environments for the diversification and colonisation of charophytes, ostracods, gastropods, fish, and an ample herpetofauna. The abundance and diversity of eggshells also suggest the development of nesting areas, whereas the occurrence of charred cheirolepidiacean conifer would indicate intermittent wild fires linked to drought events. The taxonomic breadth of this ecosystem is characterised by the taxonomic distinctness index, which, in turn, becomes a referential model to which other Lower Cretaceous microfossil sites may be compared.

Viability assessment and estimation of the germination potential of charophyte oospores: testing for site and species specificity

Anthropogenic disturbance over several decades has caused aquatic ecosystems to deteriorate, raising concerns about their condition and, consequently, prompting restorative activities. The recovery of submerged vegetation (notably charophytes) is a crucial requirement for the restoration of eutrophic aquatic systems. The success of this action often depends on the availability and germinability of aquatic plant diaspores. To characterize the potential of the diaspore bank for the restoration of charophyte stands, we investigated viability, germination potential and conditions for dormancy breaking of the oospores in three independent studies. The viability of the oospores was determined by means of the triphenyltetrazolium chloride (TTC) test. The germination potential of the diaspore banks from seven locations was estimated for potential irradiance dependency and the impact of factors influencing the dormancy status was assessed. For the latter aspect, the germination experiments were conducted with solitary oospores from plants and diaspore banks, pretreated under different temperature and desiccation regimens. The results showed species-specific differences in dormancy breakage and germination of 10 charophyte species. Five of the species tested, Chara filiformis Hertzsch, Lychnothamnus barbatus (Meyen) Leonh., Tolypella glomerata (Desvaux) Leonh., Nitella mucronata (A.Braun) Miq. in Hall and Nitella flexilis (L.) C. Agardh/Nitella opaca (C. Agardh ex Bruz.) C. Agardh, exhibited light-dependent germination. The irradiances where maximum germination was achieved correspond well to the species’ distribution within the vertical irradiance gradient in their habitats.

Biogeography of Chilean Charophytes – determined by climate or by water chemistry?

Distinct distribution patterns were observed for several species of charophytes during a survey in Chile. We attempted to link these patterns to climatic conditions, but no direct causality between specific climatic factors and charophyte growth conditions could be identified. In this paper, correlations between water chemistry and occurrence of charophytes were tested as an alternative approach to explain the distribution pattern. Datasets with information about conductivity, alkalinity, pH and concentrations of calcium, magnesium, sodium, potassium, sulphate and chloride from sites inhabited by at least one charophyte species were analysed by principal component analysis. The results show that the distribution patterns of at least some species can be explained by niche differences with respect to water chemistry. The genera Chara and Nitella are in general well separated by their preferences for a given pH, alkalinity and conductivity range. Within the genus Chara, Chara squamosa, Chara braunii, Chara fulgens, and a yet unidentified taxon Chara sp., differ from this genus-specific pattern with respect to at least one parameter, whereas Chara vulgaris occupies a broad niche, covering almost the full range of all parameters except conductivity. Within the genus Nitella, niche separation by water chemistry was only possible between Nitella tenuissima and Nitella asagrayana. The chemical niche of Chara braunii was more closely related to the niche of the genus Nitella than the niche of other Chara species.

Palaeoenvironmental significance of charophyte gyrogonites from Laguna de Gallocanta (Aragón, Spain)

At a distance of about 170 km from the Mediterranean, the inland salt lake Laguna de Gallocanta (995 m a.s.l.) is an important stop-over for thousands of migratory water birds and represents an athallasic occurrence of Lamprothamnium papulosum (Wallr.) J. Groves and Chara galioides DC., which were recorded growing in the lake until 1990. These two charophyte species are typically also known from Mediterranean coastal brackish water sites. The material studied here consists of (i) gyrogonites collected from surface sediments in Laguna de Gallocanta and (ii) fossil gyrogonites recovered from the upper 35 cm of a 75 cm core obtained from the lake. Detailed morphological and biometrical analysis of L. papulosum is provided and compared with previous data from South France. The size and shape of the gyrogonites from Laguna de Gallocanta differ greatly from populations growing in coastal sites. These differences are considered to be an adaptive morphological response to the particular hydro-chemical conditions prevailing in Laguna de Gallocanta whose salinity is due to the outwash of sulphate-rich waters from the underground. The distribution and frequency changes of the charophyte species along the core profile allow inferring palaeoecological changes marked by lake-level lowering and increasing salinity.

Taxonomical analysis of closely related species of Chara L. section Hartmania (Streptophyta: Charales) based on morphological and molecular data

In this study, five charophyte species belonging to the genus Chara L. section Hartmania, collected in Poland, were examined to determine their taxonomic status. Oospore dimensions of all investigated species differed significantly in their length, width and number of striae. However, no clear differences were found in the case of the oospore wall ornamentation that could be used for clear differentiation of the studied species. Detailed SEM images showed that the ornamentation on the oospore wall is not species specific, and also does not allow for differentiation of the species. Moreover, molecular phylogenetic analyses based on the matK and atpB DNA sequences reveal that the five studied species of section Hartmania are closely related and exhibit low genetic variation. Both types of analyses, based on oospore morphology and DNA barcoding, suggest a close phylogenetic relationship among the investigated species. The low levels of variability between species suggest that they had a relatively recent common ancestor, and probably exhibit a still incomplete, speciation process.

New insights into the ecology and phenology of two Characeae: N. opaca (Bruzelius) C. Agardh and N. gracilis (Sm.) C. Agardh

The study addressed the ecology and life cycle of two charophyte species, which are both at risk of extinction and on several Red Lists in Europe. Populations of Nitella opaca and N. gracilis, sometimes occurring together in three wetland ponds, were monitored for several years, and environmental data were also recorded. The pattern and timing of emergence (new shoots) and maturation of the sexual organs (antheridia, oogonia, and ripe oospores) were determined on plant samples collected regularly. The species phenophases were related to the environmental data. The results showed that species distribution can be linked to the water calcium content, a parameter that most differed in the three ponds. N. gracilis developed population only in ponds with very low calcium concentrations, whereas N. opaca had a wider tolerance. Following a pond bed air exposure in previous year, dense populations of N. opaca and N. gracilis were observed. None, or only a few individuals, were found when the waterbodies remained flooded the whole preceding year. Light and temperature affect differently the emergence of sex organs and the maturation of oospores. Both species differed in the timing of their phenophases. N. opaca appeared in March, reproduced and disappeared in July. N. gracilis was generally observed later in spring, and after full reproduction, the plants started a second cycle in late summer, while new oospore germination occurred. N. gracilis was perennial and reproduced all year long. Taking these results into account will help to design conservation plans for N. opaca and N. gracilis.

Significance of shallow-marine and non-marine algae stable isotope (δ18O) compositions over long periods: Example from the Palaeogene of the Paris Basin

In this study, we test the potentiality of using dasycladales and charophytes, calcareous shallow-marine and non-marine algae respectively as palaeoclimatic recorders. These algae mineralize their carbonate during short periods in summer. Throughout the Palaeogene, we compare the δ18O variation of these two taxa to identify a possible common factor influencing their isotopic composition, i.e. temperatures variations, from a local environmental signal. We sampled and isotopically analyzed eight species of charophytes and seven species of dasycladales from 23 formations ranging from the Palaeocene to the Oligocene series of the Paris Basin. By comparing the δ18O of these two groups living in different environment with that of shallow-marine mollusks from a previous study, we show that temperature variations are the main factor influencing their δ18O compositions and that local environmental effects do not screen the global thermal signal. Maximum annual palaeotemperatures are calculated from the δ18O of the dasycladales and indicate by comparison with the data from mollusks previously analyzed that dasycladales species used probably mineralized their carbonate in equilibrium with sea-water. Dasycladales recorded the global climatic events already known for the Palaeogene, with high temperatures reached during the Early Eocene and Middle Eocene climatic optimums and relative cooling intervals during the Lutetian, the Priabonian and the Rupelian. Charophyte gyrogonites also recorded temperature variations in their δ18O compositions but reconstituting reliable temperature values in non-marine environments is not directly possible and requires constraining δ18O of local continental water using other proxies. These promising results show that carbonates mineralized from algae constitute a reliable support for palaeoclimatic information and should be more widely used in the fossil record.

Charophytes in the estuarine Curonian Lagoon: Have the changes in diversity, abundance and distribution occurred since the late 1940s?

Abstract The results of the recent (2014-2015) inventory and three historical datasets (1949-1959, 1960-1980 and 1997-2007) were analyzed in order to track the long-term changes of charophytes in the largest estuarine lagoon of the Baltic Sea. The present species composition of charophytes in the estuarine part of the Curonian Lagoon consisted of 7 species, including tolerant to salinity (Chara aspera, C. contraria, C. globularis and Nitellopsis obtusa) and typical brackish-water species (Chara baltica, C. canescens and Tolypella nidifica). The highest congruence of species was between the 1997-2007 and 2014-2015 datasets, which covered respectively eutrophication and post-eutrophication periods. The 1949-1959 dataset (closest to the reference conditions) differed by the absence of typical brackish-water species. The 1960-1980 dataset (the major period of eutrophication) was relatively poor in study sites and species. During the last 6 decades, only tolerant to salinity freshwater species were constant and abundant; only Nitella mucronata can be considered as extinct. Recently, C. contraria became dominant and widespread. The changes in the charophyte species composition, abundance and distribution can be explained by different intensity of surveys and/or density of study sites, but also by the increased exposure to brackish waters since 1980s and/or recently reduced effect of eutrophication.

Report on Charophytes from rice fields in northern Italy including the alien species Chara fibrosa ssp. benthamii

The paper describes the discovery in rice fields of northern Italy of three species of Charophytes rarely reported in Italy, Chara fibrosa ssp. benthamii, a tropical taxon not native to the European Charophyte Flora, previously recorded in Italy only once, in the nineteenth century, Nitella translucens and N. mucronata.

Changes in submerged macrophyte colonization in shallow areas of an oligo-mesotrophic lake and the potential role of groundwater

Groundwater influx can significantly contribute to nutrient budgets of lakes and its influence is strongest in shallow littoral areas. In oligo- or mesotrophic systems, additional nutrient supply by groundwater influx may affect benthic primary producers and their interactions. Potential changes can be expected in community composition, biomass, stoichiometry and interactions between submerged macrophytes and epiphyton.This study aimed at investigating whether enhanced epiphyton growth at sites with groundwater discharge may have contributed to a significant change in shallow littoral macrophyte abundance reported from oligo-mesotrophic Lake Stechlin during the last 50 years. In the 1960s, shallow littoral areas were dominated by small charophyte species such as Chara aspera, C. filiformis and C. rudis. Recent mappings indicated a strong decline of this shallow water charophyte community from 42ha to 3ha and a shift to the occurrence of macrophyte species typical of eutrophic lakes such as Potamogeton perfoliatus, P. pectinatus and Myriophyllum spicatum. We analyzed the nutrient content of macrophytes, and measured epiphyton growth at sites with different groundwater influence. Water column nutrient enrichment may have increased the abundance of eutrophic species, but this did not explain the decrease of charophytes. Our data suggest that enhanced epiphyton growth in shallow littoral areas with groundwater influx could impair the development of small charophytes by shading, increasing drag forces and the charophytes’ sensitivity to herbivory.