Aquatic Botany最新文献

Seagrasses are foundation species in coastal ecosystems promoting biodiversity and community structure. Future marine carbonate chemistry under ocean acidification may enhance seagrass physiology, but little is known about how reproductive ecology and disease will integrate into future ocean conditions. A novel pathogen, Phytophthora gemini, infects >90 % of eelgrass, Zostera marina, surveyed in Northern Atlantic and Mediterranean populations reducing annual germination 6-fold. Our study investigated the combined effects of ocean acidification and P. gemini infection on germination of eelgrass seeds. We conducted a two-level factorial experiment crossing four pH levels (∆0, - ∆0.3, - ∆0.6, -∆0.9; relative to the average pH at the sampling site) with three infection levels (infected, non-infected, exposed) to determine germination rate and infection response. Prior to experimentation, flowering shoots were collected and held in flow-through seawater tanks where seeds ripened naturally. Once collected, seeds were held in copper sulfate solution (27.37 ± 1.57 ppt) and stored in darkness to mimic winter dormancy (4 °C). Before the start of the experiment, viable seeds were cultured on oomycete selective growth media to determine infection status. By the end of the experiment, 100 % of tested seeds, regardless of treatment, contained P. gemini. Germination rate significantly increased with decreased pH. Our findings indicate that P. gemini is not inhibited by ecologically relevant changes to carbonate chemistry and standard handling practices can result in effective and highly virulent disease transmission. These results confirm perennial populations of eelgrass are susceptible to infection and alerts conservationists to additional considerations necessary for successful eelgrass restoration.

Natural or anthropogenic movement of plant species outside their historical ranges may result in exposure to new environmental conditions and a lack of natural enemies, thus promoting their establishment and spread into new areas. A biogeographical comparison of native and invasive populations can provide insight into the mechanisms of successful invasions and guide effective management strategies, such as biological control, by targeting plant traits that promote invasiveness. We studied the Eurasian aquatic plant, Nymphoides peltata, in situ in the native (China, Korea) and invaded (USA) ranges to determine whether there were differences in natural enemy attack rates (percent leaf damage, frequency of leaf herbivory or disease), productivity (plant cover, reproduction), and leaf traits (leaf elemental content, leaf toughness, dry matter content, specific leaf area) between areas. We also investigated whether there was evidence of a tradeoff between natural enemy attack and growth or reproduction, as would be predicted by invasion theory. Plant cover (23–29 % higher) and reproductive output (eight times more seeds / m²) were consistently higher in the invaded range. Leaf traits consistently differed between ranges, which we would expect if plants in the invaded range had fewer herbivores or other pests. The amount of leaf damage present was similar between ranges, but the frequency of herbivory was 50 % greater, on average, in the native than invaded range. Although we did not quantify suppression of N. peltata by natural enemies, we found evidence of more frequent herbivory in Asia and reduced reproduction and plant cover compared to the USA, which supports further investigation into viability of biological controls.

Cultural eutrophication is the main cause of the decline of submerged plants in freshwater ecosystems. While many studies have focused on the nutrient uptake by the roots of these plants, less attention has been given to the effects of eutrophication on root structure. We designed a mesocosm experiment with Eurasian watermilfoil (Myriophyllum spicatum), a submerged plant indigenous to the Eurasian continent. The responses of plant functional traits, including growth traits, morphological traits and root topological indices, to different nitrogen (N) and phosphorus (P) concentrations were elucidated. We found that high P concentrations suppressed all the morphological traits and reduced the root topological traits, whereas N concentrations had a comparatively minor effect. Although the root branching of M. spicatum did not change, its root topology became more dichotomous with fewer exterior root links being formed in nutrient-rich habitats, and the root form changed from deep and thin to shallow and dense with increasing P concentrations. The root nutrient absorption ability of M. spicatum may decrease with cultural eutrophication, and this change most likely reduces its anchoring ability and increases its sensitivity to dislodge from the sediment if disturbed by hydraulic forces.

Marine natural resources are increasingly demanded to support the livelihoods and wellbeing of humans facing multiple and simultaneous crises across the planet. Seaweeds, in particular, are renowned sources of bioactive marine compounds used for various purposes, including human and animal nutrition, soil fertilization, and healthcare markets. DNA-based tools are being adopted in integrative taxonomy and ecological research, as well as to monitor the supply chain of commercially important species. This research provides novel insights into the population genetics, phylogenetic relationships, and haplotype network of six commercially significant seaweed species that are abundant in the Azores archipelago and currently traded for industrial applications. This study provides a detailed assessment of the genetic diversity of the red seaweeds Asparagopsis armata, Asparagopsis taxiformis, and Pterocladiella capillacea, and the brown seaweeds Halopteris scoparia, Zonaria tournefortii, and Cystoseira pustulata, contributing with 17 newly generated barcodes of COI, rbcL, and 28 S rDNA gene records from the Azores region to the reference databases. Understanding the species identification and population dynamics is critical for understanding species composition in biodiversity hotspots. This knowledge supports taxonomy, conservation, environmental protection, and the sustainable use of marine resources.

Carnivorous plants in the genus Utricularia (bladderwort) are diverse and widespread, represented in North America primarily by free-floating aquatic species. In the Nearctic ecoregion, roughly corresponding to temperate North America, there are 20 species of Utricularia, comprising a small fraction of the approximately 270 species in the genus worldwide. However, despite their low number, the Nearctic species represent seven of the 18 taxonomic sections of Utricularia, a pattern that potentially reflects multiple ancestral dispersal events into North America. Most of the Nearctic bladderwort species are represented by DNA sequence data, yet there is no single genetic locus that has been sequenced for all species, and this has precluded a thorough evaluation of their phylogenetic relationships. In this study, we obtained DNA sequence data for genetic loci and species that had not been sequenced previously, to produce a fully sampled molecular phylogeny. The resulting phylogeny includes all species that occur in the USA and data from five DNA regions: one nuclear locus (internal transcribed spacer, ITS) and four plastid loci (trnK/matK, rpl20-rps12, rps16, and trnL-trnF). We recovered a close relationship between U. inflata and U. radiata, two species that both have aerenchymatous floral support structures, and which previously had not been sequenced for any of the same genetic loci. We also sequenced numerous U. macrorhiza individuals, and our data support the phylogenetic distinctness and molecular diagnosability of this species against U. australis, U. tenuicaulis, and U. vulgaris. Curiously, we discovered plants in Ohio, USA that were identified as U. tenuicaulis and U. × neglecta (= U. tenuicaulis × U. vulgaris), and these represent the first evidence of such plants being naturalized in North America. These previously overlooked species and hybrids highlight the importance of using DNA in plant surveys and the value of having a robust reference library of DNA sequences.

Recent recurrent inundations of holopelagic Sargassum species (sargasso) in the tropical North Atlantic warrant studies to increase our understanding of this phenomenon. We carried out a multidisciplinary study to determine the drift and associated biota of sargasso rafts in nearshore waters of a reef system in the Mexican Caribbean, during the 2020–2022 influx seasons. Home-designed trackable drifting buoys revealed notorious influence of winds stronger than 4–5 m s⁻¹ on the rafts´ displacement. At lower wind velocities, the drift was almost entirely determined by currents; local topography played a role in concentrating or dispersing the algae. Video cameras attached to the drifting buoys allowed for non-invasive identification of free-swimming ichthyofauna, recording low specific richness with a dominance of species of the Carangidae family. Sargasso associated biota was sampled with a dipnet. The small motile macrofauna was abundant and diverse, with a dominance of few species. Epibionts (epifauna and epiphytic algae) showed low specific diversity, while the microbial communities were dominated by (potentially pathogenic) Vibro spp. Small motile macrofauna was the only biota group with new records for the study region. Differences among sampling events were observed in the associated community; suggesting large inherent variability of the rafts´ biota. The information on wind, coastal hydrodynamics and topography on the displacement of the sargasso rafts will allow for better predictions of strandings, and information on associated non-native biota or dominant microbial species helped identify groups that should be closely monitored; thereby aiding in targeted management actions for mitigating the impacts of the inundations.

The phenology of Laguncularia racemosa (L.) Gaertn. (Combretaceae) was investigated from a population located near the species’ northeastern range limit in Florida. Height, leaf dimensions, and the number of flower buds, flowers, and propagules were recorded, on average, every 2–3 months from May 2021 to October 2023. Irradiance, temperature, and inundation depth were measured hourly with data loggers and compared among seasons and years. Although plant heights were negatively impacted by freeze events in 2022 due to defoliation, vertical growth rates were significantly greater following the freeze. Flower bud and flower production were observed during the summer months and differed among years with greater abundances in 2021. Propagules were recorded in summer and autumn with greater abundances in 2021 and 2022 than in 2023. Light intensity was unlikely to limit growth without a canopy of L. racemosa. Maximum inundation depths > 1.2 m were recorded in autumn and winter when propagule dispersal was likely to occur. The greatest depth of 2.2 m was more than the tallest individual in the study and occurred when hurricanes coincided with extreme high tides. The L. racemosa population was resilient to freeze and flooding events suggesting that population densities may continue to increase in northeastern Florida marshes.

Althenia (Potamogetonaceae) is a small genus of aquatic angiosperms from saline environments that includes the most recently evolved seagrass, Althenia marina. One or two species occur in Europe, both rare and considered Data Deficient at the regional level. We report the first records of Althenia in Portugal since 1853: two populations in the Algarve and a third in central Portugal. As in previous studies, all Portuguese populations include plants with and without visible nerves in the leaf sheaths, a character used to distinguish between A. orientalis and A. filiformis. We tentatively recognize a single Althenia species in Eurasia, pending further studies. We recommend further searches of suitable habitat, as Althenia species are small and easily overlooked, as well as monitoring and safeguarding of known populations through in situ and ex situ conservation.

Spate floods control sediment, nutrient and biodiversity patterns in river floodplains, but the diachronic effects of spate floods on these compartments are rarely assessed. The effects of a 10-year flood spate on substrate characteristics and aquatic vegetation (community composition and life-history traits) were assessed before and after the spate in eleven former river channels that had become wetlands and varied in flood frequency. The effects of spate flooding on sediment and vegetation were expected to be greater in the less frequently flooded channels. For life-history traits, we expected a greater effect of the flood on tall evergreen species with high leaf area, while species with ruderal traits were expected to be less affected. For sediments, the flood reduced fine sediment cover and organic carbon content, but did not affect nutrient content. Vegetation cover decreased particularly in the most and least frequently flooded channels. Species richness and functional indices were little affected. The disturbance had a significant effect on plant traits, reducing tall evergreen species. This effect on plant characteristics increased as the frequency of overflow increased. The results highlight the key role of erosive floods in maintaining poorly competitive aquatic plants and limiting successional processes in riverine wetlands. Given the importance of plants in maintaining spate floodplain biodiversity, these erosive spate floods are essential to maintain or restore in a context of extreme river regulation.