Aquatic Botany最新文献

Natural disturbances and human activities frequently fragment aquatic plants. Vegetative fragments of invasive clonal plants have a high capacity for colonization and regrowth, which results in rapid spreading of these plants. A case study was conducted to explore the effects of the water level and light on the colonization and regrowth of a clonal invasive plant – Alternanthera philoxeroides. In the study, the growth of 10-cm-long fragments of A. philoxeroides was followed in three water levels (0, 2, and 10 cm) and two light conditions (10% and 80% of natural light). Results showed that total biomass of A. philoxeroides under all treatments except 10% of natural light and 10 cm of water level was higher than the initial biomass, which suggested that fragments of A. philoxeroides can regrow under most conditions. However, treatments of high water levels and low light inhibited regrowth, clonal expansion, and vegetative propagation of clonal fragments by reducing their total biomass, number of nodes and storage root biomass. Creating habitats of high water levels and low light, for example, by planting native emergent aquatic plants, can hamper the spread of this clonal invader. Our study contributes a new perspective to controlling the spread of invasive clonal plants by creating habitats that inhibit the colonization of invasive plant propagules.

Azolla is an aquatic fern that has a symbiotic association with nitrogen-fixing cyanobacteria. It is mainly used as a biofertilizer in rice; however, its potential under salt-affected rice cultivated area was compromised. Therefore, the present study was undertaken to understand the effect of salinity stress on morpho-physiological, biochemical characteristics, photosynthetic efficacy, nutrient and High Affinity Potassium Transporter (HKT) genes in Azolla. The results indicated that out of 102, 8 Azolla (A. microphylla, BLCC 5, BLCC 18, BLCC 28, Pa Car WTY, R 18, R 54 and R 59) were found tolerant to 80 mM NaCl. The best species for salt tolerant (80 mM NaCl) was A. microphylla, whereas the least-tolerant was A. rubra. Fresh biomass production, frond length and width in A. microphylla were significantly (p < 0.05) higher in A. microphylla than A. rubra in both 40 and 80 mM NaCl. Moreover, chlorophyll a/b ratio, carotenoids and chlorophyll fluorescence (CHF)-derived F_O, F_m, F_v/F_m and root architecture (root length, average root diameter, root volume, projectile and surface area) were higher in A. microphylla than A. rubra under 40 and 80 mM NaCl. Contents of Na⁺ and Ca²⁺ increased in both A. microphylla and A. rubra, which can interfere with the uptake of essential macronutrients; however, these were accumulated comparatively less in A. microphylla than A. rubra, whereas a reverse trend was observed in cellular accumulation of K⁺ content. A. microphylla had higher superoxide dismutase (SOD), ascorbate peroxidase (APX), and proline activities in 40 and 80 mM NaCl than A. rubra. For the first time, twenty six HKT primers were designed as a molecular marker to identify salt-tolerant Azolla. Out of these, three HKT primers (Req 6, Aeq14, and Aeq16) were amplified in A. microphylla under NaCl stress, while their amplifications were not observed in A. rubra (salt susceptible). In A. microphylla, the expression of the Req 6 (HKT) gene were more under NaCl stress. Moreover, further research is needed to discover and validate the biochemical and molecular processes that confer salinity tolerance in Azolla plants.

Arbuscular mycorrhizal (AM) fungi often colonize the roots of mangrove plants, forming symbiotic associations with them, but colonization rates differ greatly among mangrove species. To examine differences in the colonization patterns of AM fungi, we focused on two species of mangroves (Rhizophora stylosa and Bruguiera gymnorhiza; Rhizophoraceae) and conducted a pot experiment using seedlings grown in mangrove soil watered with fresh water or brackish water (200 mM NaCl). We observed AM fungal structures such as hyphae, arbuscles, and vesicles in the roots of all B. gymnorhiza seedlings in the freshwater treatment, but rarely in the brackish water treatment. By contrast, we found no AM fungal structures in roots of any R. stylosa seedlings in either the freshwater or brackish water treatment. These results imply that B. gymnorhiza are facultatively mycorrhizal plants that have maintained the ability to form associations with AM fungi, whereas R. stylosa, which dominate habitats more seaward than those of B. gymnorhiza, may have lost the ability to form mycorrhizal associations through adaptation to extreme seaside conditions.

Myriophyllum spicatum, Eurasian watermilfoil, is a submerged aquatic plant invasive to North America. Several characteristics found in M. spicatum provide reasoning behind its invasion success such as its ability to spread and grow rapidly as well as displace other surrounding native species. However, Eurasian watermilfoil’s effects on ecosystem functioning (such as dissolved oxygen) and how such functioning differ from effects of native vegetation have seldom been studied. Using data collected in field, we used statistical models including Gaussian multivariate linear effect models and structural equation modelling (SEM), to investigate the effect of vegetation type and cover on dissolved oxygen (DO) and temperature gradients. Here, we show that invasive Eurasian watermilfoil colonies, relative to native submerged vegetation, can have a direct effect on DO gradients. These changes in DO conditions were driven by both an increase in surface oxygen concentrations and a decrease in bottom layer oxygen concentration in dense M. spicatum vegetation. Furthermore, we find that the differences in DO gradients could be predicted from M. spicatum’s direct impact on oxygen concentration and not indirectly via its effects on water temperature. Our results demonstrate that dense colonies of M. spicatum can directly affect DO concentrations and may do so more than native macrophytes which could explain its rapid spread and potential impacts on ecosystem functioning.

In mangrove forests, the hydroperiod is strongly related to tidal dynamics, where the periodic oceanic water movement regulates the level, duration, and frequency of the flooding events. In fringe mangrove forests, Rhizophora mangle propagules deal with variable hydroperiod conditions that sometimes compromise their survival. To disentangle the combined effects of duration and intensity of flooding on physiological and growth variables, we imposed a continuous experiment with three levels of flooding and four flooding durations on seedlings of R. mangle. We collected data at 3 and 6.5 months after exposure to the treatments. Propagule reserves allowed plants to evade the effects of the flood level after a 3-month treatment period. After a 6.5-month exposure, physiology and growth were modulated by the flooding time. Individual plants had higher stem length and lower root and total biomass at prolonged and high flooding levels compared to any other flooding combinations. In both ages, the highest total plant biomass was exhibited in the medium flooding levels and 6 h flooding duration. The plasticity index was higher for morphological and biomass variables than for physiological variables. The high morphological plasticity of R. mangle plants constitutes a competitive advantage to colonize flooded sites in fringed mangrove areas. Our results identify schemes to improve the success of mangrove restoration plans, a critical tool for carbon sequestration and ecosystem service provision.

Germination biology and dormancy-breaking requirements of fully aquatic (submerged and floating) plant species remain relatively understudied. This is a significant impediment to efforts to restore vegetation in freshwater systems, where the abundance of seeds, and possibility of sowing them in large numbers, suggests underutilized potential for active revegetation. We assessed the influence of seed traits (mass and shape) and two treatments to break dormancy (scarification and gibberellic acid) on the germination of seeds of four macrophyte species after cold-stratification. For all species, untreated seeds did not germinate (0% rate), despite relatively high seed viability (42–90% across species). For Potamogeton illinoensis and P. natans, scarification plus gibberellic acid increased germination the most, to 83% and 35%, respectively (corrected for viability). The other two species remained wholly (Brasenia schreberi) or overwhelmingly (Nuphar variegata) ungerminated. For the two species that did germinate, germination probability increased with seed mass (P. natans and P. illinoensis) and elongation (P. natans). While the small size of trait effects relative to seed treatment effects suggests the latter are more important for revegetation work, the trait patterns highlight evolutionary tradeoffs in seed-size investments. The two Potamogeton species we examined show promise for use in revegetation via seeding, whereas B. schreberi and N. variegata dormancy break has not been adequately developed for these species to be used in seeding-based revegetation.

In 2012, Hurricane Sandy struck Barnegat Bay, New Jersey damaging extensive beds of Zostera marina and causing major benthic ecosystem disruptions. Pre-Sandy genetic surveys of eelgrass populations in Barnegat Bay indicated low heterozygosity and connectivity with high levels of inbreeding. After such devastation, we became concerned with the long-term fate of these populations and in previous work examined the present genetic condition of eelgrass in Barnegat Bay. Counter to our expectations, the 2021 Z. marina populations were more diverse, had greater connectivity and less inbreeding than the populations from 2008. These results further motivated us to examine the trajectory of changes between 2008 and 2021 through additional investigation of archival Z. marina samples from 2013 and 2017. This present study tracks the trajectory of Barnegat Bay eelgrass population genetics before and after Hurricane Sandy. Immediately post Sandy, populations were already more diverse with heterozygosity closer to Hardy-Weinberg Equilibrium; by 2021, two populations, Oyster Creek and Ham Island, demonstrated a surplus of heterozygotes. Similarly, in 2013 there was a three to eight-fold reduction in inbreeding observed with clear outbreeding by 2017. There was no evidence of recent bottlenecks in any population, although Oyster Creek and Ham Island populations manifested historical bottlenecks. Our evidence supports that genetic recovery was already underway a year after Sandy.

Every introduction of a non-indigenous species (NIS) in coastal environments poses a threat to the native species and communities, as its effects in the ecosystem are not readily predictable. Introduction rates have kept increasing in the last decades, and our finding of the brown alga Mutimo cylindricus in the Canary Islands is another example of this general trend. This work represents the first record of the species outside its native range (Japan, Korea and the Philippines) in half a century, since its report in 1973 in Baja California, and marks the first report of M. cylindricus in the Atlantic Ocean. We analyzed the morphology of a male gametophyte observed in the Canary Islands and its phylogenetic relationship with other known populations using rbcL and cox3 genes. The morphology of M. cylindricus in the Canary Islands is consistent with previous descriptions and the phylogenetic analyses revealed the close relationship with native populations from Japan. The finding of a male gametophyte is noteworthy, as introduced and some native populations of this species are composed exclusively by female gametophytes and thought to be parthenogenic, whereas androgenesis is considered rare in the field. Maritime traffic appears as the most apparent introduction vector of the species and it seems plausible that microscopic crustose sporophytes were present near the collecting site, highlighting the need of further monitoring of the invasive potential of this species in the Atlantic Ocean.

To meet the increasing demand for kappa carrageenan, several strategies have been employed to improve eucheumatoid seaweed productivity, such as nutrient enrichment (NE) and the application of some efficient farming methods (FM). This study aims to investigate the interaction of NE (applied as ammonium phosphate at 3.5 g L⁻¹) and farming method on the performance of the eucheumatoid seaweed Kappaphycus alvarezii. Three farming methods, that is, Sway (SW), Spring (SP), and modified fixed-off bottom (MFOB), were employed for nutrient-enriched (NE) and non-enriched control fronds for a period of 45 days. NE significantly improved the growth and carrageenan yield of the seaweed and afforded protection against the incidence of ice-ice disease; meanwhile, the effect of FM and NE-FM interaction was non-significant. NE increased the gel strength of the extracted carrageenan; meanwhile, SP farm led to the highest gel strength, followed by MFOB.