:: E. DODINET, S. NADOT Editorial Paru dans Botany Letters, 2018, 165 (1), pp. 1-1. Anglais Abstract This first issue of 2018 is dedicated to a focus on extant and fossil Charophytes.
:: R. THOMPSON Letters to the twenty-first century botanist. Second series: “What is a seed? – 1” Paru dans Botany Letters, 2018, 165 (1), pp. 3-5. Anglais :: M. BEILBY, S. C. SCHNEIDER, A. PUCKACZ & C. MARTÍN-CLOSAS Towards an integrated understanding of charophyte biology and paleobiology Paru dans Botany Letters, 2018, 165 (1), pp. 7-10. Anglais Abstract In this special issue, we present an overview of the presentations given at the 7th Meeting of the International Research Group on charophytes held in Astana in 2016. Charophytes, understood as the members of extant Charales and their direct ancestors (fossil orders Sycidiales and Moellerinales), represent a significant plant group that provides an iconic research system for many diverse fields, such as evolution, ecology, electrophysiology, phytoremediation and management of wetlands. Charophytes have been proposed as one of the closest ancestors of land plants. Their fossil record goes back to 425 Ma (million years ago), but the rise of the oldest living charophyte genera is dated from ca 155–125 Ma. An example of vegetations already dominated by early Characeae has been recently found in China, dating back to that time. The definition of charophyte species has been a matter of debate, since the morphology of these plants shows a great plasticity. The elucidation of charophyte taxonomy is of major importance for the definition of endangered species. New light is shed by the use of genetic coding for the distinction of problematic species within the Chara genus. Climate change is one of the major concerns in the present scenario of disturbance of charophyte habitats. Specific adaptations, including changes in thallus morphology, parthenogenesis and enhanced production of oospores, develop when charophyte habitats become unstable, desiccate or increase their salinity. Brackish charophytes are also a subject of special attention, since they include species highly specialized in particular niches and highly vulnerable to extreme salinities reached through habitat desiccation. The chemistry of water controls the distribution of species, even at the biogeographic scale. Experiments, related to the transport of ions across the charophyte cell membrane, provide an understanding of how charophytes adapt physiologically to those changes.
:: SHA LI, HAICHUN ZHANG, QIFEI WANG & XIAOYIN REN Early Cretaceous charophyte flora from the Chijinbao Formation in the Jiuquan Basin, Northwest China, and its stratigraphic and palaeoecological significance Paru dans Botany Letters, 2018, 165 (1), pp. 11-22. Anglais Abstract The charophyte flora from the Lower Cretaceous Chijinbao Formation (Jiuquan Basin, Northwest China) and its application to biostratigraphy and palaeoecology were investigated. The species Mesochara stipitata and Aclistochara huihuibaoensis were found in the Chijinbao Formation. The intra-specific variability of M. stipitata and A. huihuibaoensis was examined based on biometric analyses. The flora suggests a Barremian age for the Chijinbao Formation, in agreement with the data obtained from conchostracan and fish assemblages. Sedimentological, taphonomic and palaeoecological data indicate that a permanent lake occurred in the area, and that the climate was warm at the time of deposition of the Chijinbao Formation. The Early Cretaceous charophyte flora of the Jiuquan Basin was poorly diverse, especially in comparison with Europe where abundant clavatoraceans dominated the lakes and ponds of the tropical to subtropical Lower Cretaceous Central Tethyan Archipelago. Instead, the Barremian Chinese flora was dominated by a few early characeans. Differences in climate may account for such contrasting diversity.
:: C. MARTÍN-CLOSAS, A. VICENTE, J. PÉREZ-CANO, J. SANJUAN & T. BOVER-ARNAL On the earliest occurrence of Tolypella section Tolypella in the fossil record and the age of major clades in extant Characeae Paru dans Botany Letters, 2018, 165 (1), pp. 23-33. Anglais Abstract The genus Tolypella is considered the basal-most characean genus according to modern molecular phylogenies. Its fossil record, however, provides contradictory evidence since fossil Tolypella section Tolypella has its first fossil occurrence in the Late Cretaceous, about the same time as the first occurrences of other genera of living characeans, i.e. Chara, Lamprothamnium, Nitellopsis and Lychnothamnus which are considered more derived. In this study, the first occurrence of Tolypella sp. aff. T. grambastii subsp. arctica (Tolypella section Tolypella) is now documented from a lacustrine bed, in the Lower Cretaceous of the Garraf Massif (Catalonia, Spain), ca. 125.0 Ma old. This indicates that Tolypella s.s. is indeed a very old genus and that its first fossil record should be extended back at least 55 million years. The first appearance of living Characeae in the fossil record correlates well with the topology of molecular phylogenies. The basal genera Tolypella, Nitella and the ancestors of the extant Chareae represent the first radiation of the characeans during Late Jurassic–Early Cretaceous. The oldest representative of the clade of Tolypella in the fossil record, belonging to Tolypella section Rothia, suggests that the divergence of Tolypella is at least of Kimmeridgian age (157.3–152.1 Ma). The splitting of Nitella and the Chareae is dated as Oxfordian in age (163.5–157.3 Ma). The extant representatives of the crown group (Chara, Lamprothamnium, Nitellopsis and Lychnothamnus) thus represent the remnants of the second radiation of the Characeae during the Upper Cretaceous, at least 83.6–72.1 Ma ago.
:: I. SOULIÉ-MÄRSCHE, R. BAUMHAUER & B. SCHÜTT Palaeoenvironmental significance of charophyte gyrogonites from Laguna de Gallocanta (Aragón, Spain) Paru dans Botany Letters, 2018, 165 (1), pp. 35-44. Anglais Abstract 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.
:: M. J. BEILBY, V. A. SHEPHERD & M. ABSOLONOVA The role of H+/OH− channels in saline pathology of Chara australis: brief history Paru dans Botany Letters, 2018, 165 (1), pp. 45-54. Anglais Abstract The pH banding pattern, observed in Chara and Nitella early last century, suggests that there are H+ or OH− conducting channels in the alkaline bands of the characean plasma membrane. If the cells are exposed to high pH medium, pHo, these channels become the dominant membrane conductance: High pH state. Goldman-Hodgkin-Katz (GHK) equation can model the current voltage (I/V) characteristics of this state with either H+ or OH− as permeant ion. However, H+ requires unrealistically large increases in channel conductance/number parameter as pHo increases. Recently we discovered a typical spiky noise in the membrane potential difference (PD) of salt sensitive Chara australis, appearing immediately upon exposure to saline. The H+/OH− channels are thought to open transiently in small patches all over the cell, while negative membrane PD does not support their open state/s. As the membrane PD depolarizes due to inhibition of the proton pump by salinity, the H+/OH− channels remain open to dominate the I/V characteristics, which can also be modeled by GHK equation. The addition of 1 mM ZnCl2, the main known blocker of animal H+ channels, abolishes both the PD noise and the H+/OH− I/V characteristics in high pH state and in salt stressed cells. Confocal microscopy and fluorescein isothiocyanate (FITC)-dextran illuminate the pH changes around cells and reveal transient bright spots early in saline exposure, becoming more numerous and fixed in space with time in saline APW.
:: S. CALERO & M. A. RODRIGO The life cycle of a parthenogenetic population of Chara canescens from an interdunal Mediterranean pond Paru dans Botany Letters, 2018, 165 (1), pp. 55-65. Anglais Abstract Chara canescens lives in shallow brackish waters in the northern hemisphere. It has been described as an annual species that mostly reproduces by parthenogenesis, being the only species of Chara able to do so. However, much is still unknown about its life cycle and the differences between the sexual and the parthenogenetic populations. We monitored the life cycle of a parthenogenetic population growing in a brackish interdunal pond in the Albufera de València Natural Park (Spain). Approximately 30 specimens were harvested every 15–30 days throughout 2015. The longest polar axis and the largest equatorial diameter were measured, and the isopolarity index was calculated for the oogonia and the oospores. The non-swollen and the swollen oogonia were distinguished by size. This population had a short life cycle, but two types of shoots with different life history traits were found. A few small individuals overwintered underneath the emergent vegetation. In early March, new shoots appeared from the germinating oospores, growing fast and colonizing more open waters. The first oogonia appeared in April, enlarging and ripening along the first five whorls of the shoots. The oospores were produced in less than 15 days after the first oogonia emergence. The ripe oospores were small (average size ± SD: 392 ± 34 × 219 ± 24 μm; isopolarity index: 181 ± 22). Parthenogenetic reproduction lasted 5 months. No new fructifications were produced from September onwards. Although the oospores were smaller than those described in the literature for the species, they were clearly viable and enabled the persistence of the population through the winter.
:: P. NOWAK, H. SCHUBERT, A. HOLZHAUSEN, V. SOMMER & R. SCHAIBLE Morphological adaptations of Chara baltica and Chara liljebladii (Characeae) under different light conditions Paru dans Botany Letters, 2018, 165 (1), pp. 67-75. Anglais Abstract Individuals within wild populations differ substantially in their fitness as a result of either genetic differences or acclimation. Within the Charophyte algae, the two taxa Chara baltica and C. liljebladii predominate at different water depths of the same habitat. The two taxa are mainly distinguished by quantitative characteristics, pointing to light acclimation. In particular, they differ by a length of the internode and the bract cells, as well as the cortication type. Genetic analyses revealed that individuals of both morphotypes are genetically identical, and hence may belong to the same species. In the present paper, we tested a hypothesis that C. liljebladii is a lowlight phenotype of C. baltica. Can a C. baltica phenotype be transferred into a C. liljebladii (and vice versa) by manipulation of the environmental conditions such as irradiance? We observed significant changes in the morphology of C. baltica: decreasing the irradiance significantly increased the growth of the branchlets and internodal cells. Consequently, the plants grew larger, changing their morphology in the direction of the C. liljebladii morphotype. In the reverse experiment, subjecting C. liljebladii to increasing irradiances, the individuals had slightly better growth, but none of the analysed morphological characteristics changed significantly. Both taxa have thus shown different adaptations to light limitation. Their morphologies cannot be transferred into each other by environmental factors. Thus, the presence of the different morphologies reflects the ecological characteristics of their habitats, such as light availability or turbidity.
:: A. ANTAR SABER, A. BALLOT, S. C. SCHNEIDER & M. CANTONATI Morphological and molecular features of a Chara vulgaris population from desert springs on the Sinai Peninsula (Springs of Moses, Egypt) Paru dans Botany Letters, 2018, 165 (1), pp. 77-89. Anglais Abstract We studied morphology and phylogeny of a Chara vulgaris (Charophytes, Charales) population sampled from the thermal “Springs of Moses” (Ayun Musa, Sinai, Egypt). Morphology of freshly sampled and cultivated materials was compared in order to quantify the influence of culturing conditions on morphological features. Cultivated material was shorter and had a smaller internode diameter than the freshly collected material. The bracteoles in the freshly collected material were distinctly longer (about 4–12 times the length of an oogonium) than those in the cultured material (about 2–4 times). Moreover, oogonia were slightly longer in the cultured material. Genetic analysis of the matK gene clearly identified the sampled specimens as Chara vulgaris. However, the freshly collected material was found to differ from “typical” Chara vulgaris populations in one morphological and one life-cycle feature. The thalli were fairly delicate, and the antheridia were shed early in both freshly collected and cultured materials, while oogonia were still in place. Most of the plants prepared and observed in this study were found to bear plenty of oogonia, whilst antheridia were often missing. Antheridia were only present on the newly formed branchlets at the stem apex. The peculiar morphology and life-cycle characteristics of this C. vulgaris population may be adaptations to this highly isolated and selective desert freshwater habitat.
:: D. AUDERSET JOYE & A. BOISSEZON New insights into the ecology and phenology of two Characeae: N. opaca (Bruzelius) C. Agardh and N. gracilis (Sm.) C. Agardh Paru dans Botany Letters, 2018, 165 (1), pp. 91-102. Anglais Abstract 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.
:: A. BOISSEZON, D. AUDERSET JOYE & T. GARCIA Temporal and spatial changes in population structure of the freshwater macroalga Nitellopsis obtusa (Desv.) J.Groves Paru dans Botany Letters, 2018, 165 (1), pp. 103-114. Anglais Abstract Nitellopsis obtusa usually inhabits deep lakes, where the plants display vegetative growth and survive through the winter. In the present study we investigated a shallow lake where Nitellopsis reproduces sexually; we were interested in the effect of light conditions, temperature and water level on sexual reproduction of the species and its ability to survive lakebed drying. We estimated the distribution of all macrophyte species each July from 2009 to 2014 and correlated annual variations with fluctuations in hydrological conditions. We also sampled a variety of morphological characteristics of N. obtusa plants in nine periods throughout the 2009 and 2010 growth seasons and related them to water depth, day length and accumulated heat energy (growing degree-day) at the date of sampling. N. obtusa population was negatively impacted by decrease of water level, probably through the combined effects of competition with fast-growing pioneer species and lack of intrinsic ecological requirements. The fertility of N. obtusa could be interpreted as a response to disturbance in external conditions, leading to the production of long-lived and drought-resistant oospores. Development of male shoots prior to female shoots and their persistence throughout the season probably optimize the fertilization process. Sexual reproduction seems to be controlled by light and temperature conditions. An alternative hypothesis suggests that fertile and sterile populations belong to two distinct ecotypes.
:: K. HERKÜL, K. TORN & T. MÖLLER The environmental niche separation between charophytes and angiosperms in the northern Baltic Sea Paru dans Botany Letters, 2018, 165 (1), pp. 115-127. Anglais Abstract Charophytes and angiosperms are the most important primary producers and habitat modifiers in shallow soft-bottom fresh and brackish water bodies. The sheltered bays of the low-salinity northern Baltic Sea provide unique habitats, where euryhaline macrophytes of both freshwater and marine origin can thrive. The regional cohabitation of several species, with generally similar biological traits, raises questions about the mechanisms underlying the coexistence. Generally, sympatric populations rely on niche separation to reduce competition pressure that, in turn, facilitates long-term coexistence. A large benthos biomass data-set, covering the whole extent of the Estonian sea area, the northern Baltic Sea, together with a set of 13 environmental variables (bathymetrical, hydrodynamical, chemical, biological) was used to test the potential niche separation between regionally coexisting charophytes and angiosperms. A constrained correspondence analysis indicated both the grouping of some species and a distinct niche separation of others. The niche centers of angiosperms Zostera marina, Zannichellia palustris, and Potamogeton perfoliatus diverged most strongly from all the other species, while those of Chara connivens and Myriophyllum spicatum nearly coincided. Depth, salinity, and duration of ice were the most influential environmental gradients that discerned the environmental niches of the species. Comparison of the breadths of the environmental niche spaces, occupied by the studied species, showed highly species-specific results. Within the studied species, Z. palustris and Z. marina had the lowest niche specialization, and C. connivens had the highest specialization. Altogether, among the angiosperms the variability of the environmental niche breadth was higher compared to the charophytes.
:: H. SCHUBERT, I. BLINDOW, D. SCHORIES, M. MAGES, W. VON TÜMPLING & S. WOELFL Biogeography of Chilean Charophytes – determined by climate or by water chemistry? Paru dans Botany Letters, 2018, 165 (1), pp. 129-145. Anglais Abstract 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.
:: A. HOLZHAUSEN, C. PORSCHE & H. SCHUBERT Viability assessment and estimation of the germination potential of charophyte oospores: testing for site and species specificity Paru dans Botany Letters, 2018, 165 (1), pp. 147-158. Anglais Abstract 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.
:: P. NOWAK, T. STEINHARDT, U. VON AMMON, H. ROHDE, A. SCHOOR, A. HOLZHAUSEN, R. SCHAIBLE & H. SCHUBERT Diaspore bank analysis of Baltic coastal waters Paru dans Botany Letters, 2018, 165 (1), pp. 159-173. Anglais Abstract The coastal waters are important transition zones for terrestrial nutrient and pollutant runoff and the open Sea. During the last decades, eutrophication has negatively influenced macrophyte communities of the coastal ecosystems, making restoration activities inevitable. This study analysed recent macrophyte vegetation and the reproductive potential through the sediment diaspore reservoir along the German Baltic Sea coastline. Salinity was identified to be the responsible factor for shifts in the macrophyte community with most commonly found species like Stuckenia pectinata or Myriophyllum spicatum. In contrast, the oospores of small charophytes (e.g. Tolypella nidifica) clearly dominated the sediment diaspore bank. The germination rates differed in the recent vegetation composition and the diaspore bank composition with Zannichellia palustris as the dominant species. However, several species not visually detected at the respective sites were represented in the diaspore bank and germinated at a low rate (e.g. Chara contraria and Lamprothamnium papulosum). The maximal germination frequency corresponded to the sediment layer in which diaspore density was the highest (5–15 cm). In conclusion, the germinable diaspores were observed at all sites. Considering the differences between the diaspore composition, recent vegetation and germination success, we have illustrated the potential of the diaspore banks for the restoration of the macrophyte communities after at least mid-term periods of disturbance.
:: ANONYME List of Reviewers Paru dans Botany Letters, 2018, 165 (1), pp. 175-179. Anglais