Aquatic Botany最新文献

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.

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.