Aquatic Botany最新文献

Halophila baillonii Asch. is a rare seagrass species found in the Caribbean, Atlantic, and Eastern Tropical Pacific (ETP). It is listed as Vulnerable in the IUCN Red List yet very little is known about its dispersal mechanisms. For this study, samples were collected at five sites on the Pacific coast of Costa Rica. Each site was visited once between 2019 and 2021 as part of a larger molecular study. At each site, H. baillonii foliar shoots were manually collected along three transects. Presence of flowers or fruits was assessed for 1292 foliar shoots using a dissecting microscope. Additionally, sediment samples were collected to assess seed density at three of the sites. Flowering frequency was very low overall (0.7 %), flowers were only found at two of the five sites, and only female flowers were present. There were no fruits or seeds at any of the sites. This is the first report of H. baillonii flowering on the Pacific coast of Costa Rica and within the ETP. Meanwhile, H. baillonii flowers of both sexes and fruits have been found from limited sampling efforts at multiple sites in the Caribbean and Brazil. The findings of this study suggest a lack of sexual reproduction and potential clonality of the seagrass H. baillonii on the Pacific coast of Costa Rica. This supports the recent notion that H. baillonii is the first non-native seagrass in the ETP, yet more detailed field and molecular studies are needed.

We developed a phenology-based growth model(PG model) for Spartina alterniflora that incorporates the effects of light, temperature, and salinity on plant production. The PG model is the first to quantify carbon translocation between both above- and below-ground biomass across three phenological periods: growth, senescence, and dormancy periods. This model, fitted to field data from short, medium, and tall S. alterniflora types, estimates physiological parameters such as mass-specific rates of carbon translocation. Once parameterized, the model is applied in forward mode to predict whole-plant production, growth, respiration, mortality, and translocation. Model results reveals that short forms allocate 82 % of photosynthate to below-ground biomass during the growing season, compared to tall (52 %) and medium (22 %) types. However, tall forms, with extensive above-ground biomass, show the highest absolute carbon translocation to below-ground tissues during growth(ave. 3940 g dry weight m⁻²) and senescence(ave. 265 g dry weight m⁻²) period. An average mortality rate of 52 % of net production in the tall form below-ground biomass throughout the year indicates a substantial contribution to organic carbon sequestration within the habitat sediment. Model results also reveal that the carbon translocation from below- to above-ground tissues may not be required for survival during winter in milder climate like Sapelo Island, Georgia.

The first record of Halophila stipulacea is reported for the continental waters of the United States. In August 2024, a small meadow was identified inside Crandon Marina on Key Biscayne, Florida, USA. Following surveys have revealed that H. stipulacea has spread to adjacent areas immediately outside of the marina, often growing either in close proximity to, or interspersed with, the native seagrasses Thalassia testudinum, Syringodium filiforme, and Halodule wrightii. This serves as an initial report and extends the geographic scope of this introduced species in the Western Atlantic basin.

In recent years, global distribution of holopelagic Sargassum spp. (sargassum) has extended from the subtropical Sargasso Sea and Gulf of Mexico into the tropical Atlantic. Climate and current patterns drive seasonal and year-to-year fluctuations of biomass in the ocean, but the underlying drivers of sargassum growth are poorly understood. Previous experimental studies showed that nitrogen (N) and phosphorus (P) can be limiting to sargassum. However, iron (Fe) also limits primary production in large parts of the ocean. We therefore (1) conducted a mesocosm experiment studying the effects of N+P and Fe addition on the growth rate and nutrient content of Sargassum fluitans, and (2) compiled literature on Fe tissue levels in sargassum throughout its distribution area. The Fe levels in collected experimental specimens (Mexican Caribbean) were like those previously reported near coastlines with low terrestrial nutrient runoff, and in the open ocean. The addition of Fe greatly boosted growth, averaging 0.13 doublings day⁻¹, 40 % faster than our controls, and maximum growth rate (doubling biomass in 5½d) was 46 % above previously reported maximal value. While oceanic Fe is relatively abundant in the tropical North Atlantic during rain episodes in the summers due to Saharan dust deposition, its availability is likely more limiting during other parts of the year, particularly in the western Caribbean. However, the true limiting potential of Fe depends on many factors. Our study suggests Fe co-limitation might occur widely and urges to include Fe availability in future sargassum forecasting models.

The direct grazing of herbivores on submerged macrophytes has long been recognized as an important contributor to macrophyte loss in shallow lakes. The defense mechanism of aquatic plants against grazing laid a theoretical basis for the conservation of endangered submerged macrophytes against habitat change. Here, we aim to explore the response of the endangered macrophyte Ottelia alismoides to direct grazing by the freshwater snails Radix swinhoei by using physiological, transcriptomic and metabolomic analyses. Based on field observation, we hypothesize that O. alismoides may not have an effective grazing resistance mechanism. Our 48-h microcosm study revealed 739 differentially expressed genes (DEGs) between the grazed treatment and the control. GO annotation analysis identified DEGs with molecular functions such as signaling receptor activity and various enzyme activities, as well as biological processes including auxin signaling, responses to oxidative stress, and salicylic acid. DEGs related to phytohormones (especially jasmonic acid, JA) and antioxidant enzymes were significantly up-regulated. In addition, the 20 metabolites changed significantly after being grazed. For example, the up-regulation of the JA biosynthetic pathway led to a marginal increase of the JA content in leaves, and its signal transduction pathway was also up-regulated, consistent with that the precursor of secondary metabolism of flavonoids was up-regulated and that the transcriptome biosynthesis pathway of flavonoids was also up-regulated. Though evident defensive steps were found at the aspects of transcriptome and metabolome, leaf intactness and the photosynthetic parameters in the leaves were strongly negatively affected by snail grazing. We argued that the efficiency of those defensive strategies has probably been compromised due to the degenerative secondary metabolism in submerged leaves. Thus, to protect endangered submerged macrophytes, countermeasures for herbivory should be considered along with other important policies.

Attempts to control massive proliferations of invasive alien aquatic plants (IAAP) are often ineffective. A renewed interest for dye treatment is emerging aiming to control the submerged macrophyte Myriophyllum heterophyllum in France. We aimed to understand the effects of dye on this plant knowing about its adaptation to low light. In a 2 × 2 factorial design experiment, we assessed the effect of a dye mixture based on Brilliant Blue (E133) and Allura Red (E129) at high and low light intensities on light quantity and quality and how this might affect the plant’s performance by measuring morphological and physiological traits. A multivariate analysis identified three groups – high light (HL) plants, plants in high light with dye (HLD) or low light (LL), and low light with dye (LLD) plants. HL plants performed well but showed stress signs, with a reduced main shoot length, a higher leaf dry matter content (LDMC) and a lower nitrogen content (N), not observed in plants grown in HLD or LL. HLD and LL plants exhibited a comparable total length growth rate to those in HL, but had lower LDMC and higher N contents. LLD plants performed poorly with the lowest growth and signs of physiological stress. Dye-induced changes in light quality only marginally affected the absorbance range of chlorophyll b, which apparently did not affect photosynthesis. Commercially available dyes currently used to control nuisance aquatic plants thus seem to have little or no effect on submerged macrophytes. The presence of dye may exacerbate negative effects of very low light intensities on the plant’s growth. However, these very low intensities would only be reached during high-water levels or in winter, periods where the dye would rapidly be diluted. During summer, however, the application of dye may protect the plant from damaging light intensities and thus not be a good management strategy to control low light adapted invasive submerged macrophytes.

A combined study of morphology, stem anatomy, and the genetic markers (ITS1-ITS4 region of nuclear ribosomal DNA and rpl20-rps12 intergenic spacer of chloroplast DNA) was used to verify the identity of hybrid Potamogeton ×vilnensis Galinis previously recognized as P. gramineus × P. praelongus. Authentic herbarium material and newly collected specimens morphologically similar to the hybrid from the locus classicus (SE Lithuania) were used for comparative morphological, anatomical and molecular analyses. The study proved the paternity of P. lucens and P. praelongus and excluded the involvement of P. gramineus in hybridization and identity with P. ×angustifolius. This hybrid formula is shared with plants recorded in the Czech Republic and Denmark under the name P. ×jutlandicus Zalewska-Galosz. The site in Lithuania, known since 1961, is the first natural habitat of long-lived hybrid between P. lucens and P. praelongus whose origin has been confirmed by molecular markers. The scarce records of this taxon indicate that the knowledge of the hybrid species of Potamogeton and their distribution is insufficient and that more extensive regional studies, including molecular methods, are needed.

Seed germination is a critical process in the seed life cycle, especially for annual submerged macrophytes Vallisneria natans which is a model species for the restoration of degraded shallow lakes. Fresh seeds of V. natans have a very high germination rate but with no significant responses to the aggregation effect; meanwhile, these recalcitrant seeds quickly lose seed viability under dry storage. This study aims to explore the response of seed germination of V. natans after dry storage to aggregation effect by several microcosm experiments. We observed that seed aggregation has a significant positive effect on germination, and among the seven experimental densities between 10 ∼ 640 seeds, higher seed densities resulted in significantly enhanced germination. In contrast, daily removal of germinated seeds led to a significant decrease in the overall germination rate, suggesting that germinated seeds may secrete chemicals that promote the germination of ungerminated seeds. However, further experiments indicated that ethylene and gibberellins had no noticeable impact on seed germination, which was consistent with additional experiment results from spectrophotometer and high-throughput targeted metabolomics. We concluded that the promoting effect of aggregation on the seed germination of V. natans may be an adaptation of this species to its natural habitat but detailed mechanisms warranted further study.

This paper presents the first records of the seagrass species Ruppia brevipedunculata Shuo Yu & den Hartog in Indonesia, which has never been reported before. R. brevipedunculata from a coastal lagoon was identified based on morphological characters and phylogenetics. Indonesian R. brevipedunculata had four carpels and a short peduncle. These differentiated from R. maritima. A phylogenetic analysis of ITS and matK demonstrated the same cluster as R. brevipedunculata. That was clearly shown by the matK gene-marker. Biodiversity exploration and conservation efforts are needed to protect and preserve R. brevipedunculata and its habitat.

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.