Aquatic Botany最新文献

This research brings novel information regarding the floral traits and pollinator groups of aquatic macrophytes. Classifying functional traits and pollinator groups contributes to understanding reproductive processes, community structuring, and ecosystem functioning. Based on an extensive survey of information on 524 species of aquatic macrophyte angiosperms from the Pantanal wetland, we classified the floral traits of these species to identify their potential group of pollinators and how these traits are distributed throughout the botanical families of aquatic plants. We classified their life forms, floral traits (flower type, color, and resource), and main pollinator groups. We also investigated trends, plotting the occurrence of species throughout the phylogeny of angiosperm families, and using a network of interactions, we verified how interactions with different groups of pollinators are distributed within species traits. As a result, the species of aquatic macrophytes in the Pantanal are well distributed within the phylogeny, indicating that they may be more related to ecological than phylogenetic factors. We found a high diversity of floral traits and pollinator groups, predominating white flowers, providing nectar as a resource, and bees as their primary pollinators. Although bees were the main group of pollinators, we also found abiotic interactions linked to the species richness in Poaceae and Cyperaceae, with pollination system mainly performed by wind. Our research represents a first step towards identifying key information gaps. Future studies should focus on understanding in loco traits to fill this gap, besides information on ecological interactions with potential pollinators and species phenology.

Eelgrass (Zostera marina) is a marine angiosperm distributed in shallow seas that has a unique mechanism for regulating water content. Water transfer across the plasma membrane is facilitated by aquaporins, which are membrane proteins. In this study, we investigated the physiological functions of plasma membrane intrinsic proteins (PIPs) in eelgrass. ZoPIP1;1 and ZoPIP2;1 in eelgrass leaves were amplified by RT-PCR. Both ZoPIPs localized to the plasma membrane, and only ZoPIP2;1 showed water permeability. ZoPIP1;1 and ZoPIP2;1 were expressed in all tissues except male flowers. ZoPIPs were expressed during seed and fruit development, and their expression levels were low in mature seeds and elevated in germinating seeds. Moisture content decreased in the later phases of seed development and increased during seed germination. These findings imply that ZoPIPs participate in water uptake during seed germination. In leaves, ZoPIP expression was upregulated by dehydration but downregulated by rehydration. Water reabsorption of leaves was inhibited by HgCl₂, an inhibitor of aquaporins. These findings indicate that ZoPIPs are upregulated by dehydration during extremely low tides and promote water uptake when the tide turns. Therefore, eelgrass PIPs function in moisture regulation during growth, seed germination, and the flood-ebb tidal cycle in seawater.

The aquatic macrophyte Lemna minor and cyanobacterium Microcystis aeruginosa coexist and alternate in freshwater ecosystems, and nutrient changes, physical conditions, and micropollutants such as pharmaceuticals drive their succession. However, the effects of the antimalarial drug Lumefantrine on allelopathic interactions have not been previously investigated. This study investigated the effect of Lumefantrine on the allelopathic interactions between L. minor and M. aeruginosa. The drug adversely affected pigment levels at 1000 µg L^-1 on day one, while the highest levels were observed at the same concentration on days three and five in M. aeruginosa cultures. The intracellular hydrogen peroxide (H₂O₂) and lipid peroxidation (MDA) levels and peroxidase (POD) and glutathione S-transferase (GST) activity of L. minor and M. aeruginosa increased at varying degrees depending on the concentration of Lumefantrine. Increased concentrations of Lumefantrine induced higher microcystin content in M. aeruginosa. L. minor significantly decreased the growth and increased GST and POD activities of M. aeruginosa on day five of the assay. The introduction of Lumefantrine further altered these parameters when the species were co-cultured. Similarly, M. aeruginosa inhibited the growth of L. minor. The combination of M. aeruginosa and Lumefantrine increased GST activity compared with M. aeruginosa alone. Microcystin content was higher in co-cultures without Lumefantrine than in those exposed to the drug. These results show that allelopathic interactions between L. minor and M. aeruginosa are influenced by Lumefantrine and may have implications for managing freshwater ecosystems.

Elevated mercury (Hg) levels in biota is one issue facing the Everglades ecosystem in south Florida, USA. Methylmercury (MeHg) is a concern in the environment because it bioaccumulates through the food web and can harm fauna and humans if ingested through contaminated food sources (e.g., fish). Total mercury (THg) and MeHg concentrations were measured in several common macrophyte species, periphyton, and detritus in the Everglades to investigate Hg concentrations spatially and among different ecosystem components. At each site, two species from the carnivorous genus Utricularia, U. purpurea and U. foliosa, which are widespread and abundant in Everglades sloughs, had much higher average tissue MeHg concentrations (2.4–81 ng/g dry weight [dw]) than all other sampled macrophytes (<1.5–7.5 ng/g dw), periphyton (0.4–6.2 ng/g dw), and detritus (<1.5–5.7 ng/g dw). The Utricularia species were likewise enriched with THg (14.6–115 ng/g dw) compared to the other macrophytes (2.6–27 ng/g dw), although slough detritus had the highest THg at most sites (24–182 ng/g dw). The Utricularia species generally had a higher average percent of THg as MeHg (8.2–75%) compared to the other macrophytes, periphyton, and detritus (0–32%). MeHg concentrations in Utricularia species were quite variable among sites with a spatial distribution that generally reflected historical Hg concentration patterns known in mosquitofish (Gambusia holbrooki). Utricularia species merit further investigation to understand how they accumulate relatively high MeHg concentrations and how they might influence Hg accumulation up the food web.

Population-based threshold models may aid in quantification of germination niches under stressful conditions such as salinity, temperature, and their interactions to understand seedling emergence patterns. Seeds of Sarcocornia fruticosa, Sarcocornia alpini, and Salicornia emerici were subjected to various temperatures at different NaCl concentrations. The median base NaCl concentration was roughly steady (0.68, 0.73, and 0.70 M, respectively) at sub-optimal temperatures, then decreased linearly at supra-optimal temperatures until the ceiling temperature. The estimated base, optimum and ceiling temperatures, in water, were –0.5, 15, and 29 °C for Sarcocornia fruticosa, –2.5, 11, and 24 °C for Sarcocornia alpini, and 9.5, 25, and 40 °C for Salicornia emerici, respectively. For all species, the base temperature did not change with the salinity, while both optimal and ceiling temperatures decreased. S. emerici showed rapid and synchronized germination when salinity decreased during the rainy season coinciding with favorable temperatures.

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.