Aquatic Botany最新文献

Shallow eutrophic lakes with submerged aquatic vegetation (SAV) are a large source of atmospheric methane (CH₄) emissions. However, current estimates of CH₄ emissions from lakes are uncertain owing to the lack of data on the diel and monthly variability of CH₄ emissions. In this study, we conducted monthly diel measurements in Ulansuhai Lake, China during the ice-free period (April to October, 2019) to determine the diel and monthly variability of CH₄ emissions. The diffusive CH₄ emission flux (FCH_4d) from June to September was significantly higher (∼5- to 10-fold) than that from April, May, and October, accounting for > 92% of the total emissions. Daytime measurements would overestimate emissions if extrapolated to the whole day because FCH_4d during daytime was higher than that during nighttime. Mean daily FCH_4d emission estimates are overestimated by 25%, ranging from 11% in summer to 46% in spring based solely on daytime measurement. The sampling sites were net sources of CH₄ emissions, with total FCH₄ of 9.74 ± 9.06 mmol m⁻² d⁻¹. FCH_4d increased sharply when the water temperature was above 20 °C. FCH₄ (CO₂ eq) accounted for over 90% of the total greenhouse gas emissions (CH₄ plus CO₂), with the majority occurring from June to September. Our findings indicate that diel and monthly variations should be considered for more accurate estimation of CH₄ emissions from the lakes with SAV.

Dynamic environmental factors can influence the genetic diversity and epigenetic variation of aquatic plants, thus accelerate the rate of species adaptations. Trapa bispinosa is an aquatic crop which is widely distributed in China and worldwide, yet little is known about the genetic and epigenetic variations of T. bispinosa in fishery and nature habitats. By using AFLP and MSAP, we analyzed the genetic and epigenetic variations of 27 T. bispinasa populations in a subtropical freshwater lake. A relative high level of genetic diversity (mean H_E = 0.312, I = 0.480, PPL = 54.90%) and epigenetic variation (mean eH_E = 0.351, eI = 0.531, ePPL = 67.84%) were detected. Besides, fishery habitats maintained relative higher epigenetic variations of T. bispinosa (H_E = 0.254, eI = 0.378, ePPL = 68.28%) than nature habitats (eH_E = 0.253, eI = 0.376, ePPL = 67.77%). Overall variations were basically distributed within populations (Ø_ST = 0.260, P < 0.001). Bayesian analysis revealed a pattern of genetic structure consisting of two clusters among the populations. The Mantel regression of genetic and epigenetic variation against geographic distance did not reveal any correlations, but showed a correlative relationship with environmental variables (r = −0.47, P < 0.05). Specially, genetic diversity of T. bispinosa showed a positive correlation with slope aspect. These results indicated that habitat slope may shape the pattern of genetic variation in T. bispinosa, which further illustrated that even in a fine geographical scale, genetic diversity was unevenly distributed, restoration measurements for this aquatic crop should carefully take the habitat slope into account.

Data accessibility

All codes and polymorphism raw data are openly available from the Github repository: https://github.com/yixian185/Data-for-Trapa.

Near-shore areas face multiple stressors, effects of climate change, coastal construction and contamination. Although capping the seabed in these areas with mineral masses can reduce the impact of legacy contaminants in sediment, it can also result in the loss of flora and sessile fauna, both of which are vital components of near-shore ecosystems. Eelgrass (Zostera marina) is essential to marine near-shore areas as it supports biodiversity and mitigates the effects of climate change. Therefore, it would be beneficial to modify the top layer of caps to facilitate the reestablishment of these ecosystems when capping near-shore areas. This study describes results from an in situ, six-month field experiment conducted to compare increase in leaf length over the growing season and survival of eelgrass transplanted in two commercially available substrates (Natural sand and Crushed stone) and indigenous sediment (i.e., indigenous control sediment) in a capping project in Horten Inner harbour, Norway. Similar leaf length increase was found in Natural sand and Indigenous control sediment, both significantly higher compared to Crushed stone substrate. Survival was highest in our case in the Indigenous control sediment (120 %), with no significant difference between Crushed stone (20 %) and Natural sand substrates (25 %). These findings emphasize the importance of selecting appropriate substrate for successful seagrass restoration.

In eutrophic freshwater ecosystems, submerged macrophyte communities are replaced by phytoplankton or free-floating plants. In isolated wetlands, vegetation shift occurs over short time scales and leads to water deoxygenation and chemically reduced sediments, conditions that favor the generation, accumulation and degassing of greenhouse gases (GHGs, i.e. CH₄, CO₂ and N₂O) to the atmosphere. However, the relationship between primary producer’s growth forms, hydrological connectivity and GHGs concentration is poorly studied in the literature. A set of 18 freshwater wetlands including isolated and river-connected oxbow lakes, marshes and ponds with different vegetation growth forms was therefore monitored monthly on the annual scale. Potential GHGs diffusive fluxes towards the atmosphere were calculated and compared with direct measurements reported in peer-reviewed papers within a meta-analysis. Our results demonstrate a strong link between the colonization of free-floating plants and the onset of hypoxic conditions and accumulation of dissolved methane. Methane and carbon dioxide concentration peaked in late summer, when floating-leaved and free-floating vegetation covered 100% of the water surface. Carbon dioxide accumulation was particularly evident at hydrological connected wetlands, where nitrate pollution was likely responsible for the concomitant increment of dissolved nitrous oxide. As an increasing number of studies focuses on unravelling environmental drivers of GHGs emission from small lakes and ponds, we encourage to systematically consider the vegetation growth forms and the hydrological connectivity as major drivers of GHGs accumulation and evasion rates.

The massive pelagic Sargassum horneri (Turner) C. Agardh, 1820 has increasingly occurred in the Yellow Sea and East China Sea. Significant intrusion of floating S. horneri into the southwestern Yellow Sea, the major bloom region of the green tides, has aroused speculations on the blooming mechanism and confounded concurrent prevention practices of green tides. The floating S. horneri were surveyed and sampled throughout its distributional range to study the diversity and abundance of sympatric macroalgae, including the epiphytes and non-epiphytes. The study showed that both types of macroalgae commonly coexisted with the pelagic S. horneri and showed distinct distribution patterns. The non-epiphytic green macroalgae, primarily Ulva prolifera, were free floating with S. horneri. They were initiated from the nearshore water of Jiangsu in late April followed by a rapid accumulation and expansion as the green tide developed. The non-epiphytic green algae were mostly restricted in the western coast of southern YS with biomass decreasing evidently toward offshore. Four species in Phaeophyta were commonly detected epiphytic on the pelagic S. horneri in the survey region and Proselachista taeniiformis was dominant. Unlike the co-occurring green algae, the species composition and abundance of epiphytes have no significant variation in the distributional range of the pelagic S. horneri. High frequency (80%) and abundance (0.25 ± 0.17 g_Epi/g_Sar) of epiphytes indicated significant biological interactions with their hosts and ecological functions of this pelagic system, which deserves further investigation.

Aldrovanda vesiculosa L. (Droseraceae), or waterwheel plant, is a threatened aquatic plant species, and it is quickly vanishing from the natural distribution range in the world. There used to be many localities of the species in Japan, but it was extinct from nature in the country in 1967. The information regarding the localities in Japan was recorded in various sources, but those had not been summarized yet. Therefore, the current study reviewed herbarium specimens and literature, and we documented each location of the species, the dates of discovery and extinction, and the cause of extinction. There were 35 locations, including four artificially introduced sites, in nine prefectures. It was hypothesized that the species had spread due to floods and had been established at each locality. We testified the hypothesis using a simulation map that the plants had spread by floods in the Kanto region, the major distribution area in the country. At the same time, serious floods destroyed some habitats of the species. However, human activities more seriously resulted in habitat loss. The species collected from the localities before the extinction has been under cultivation. Restoration of the habitat and reintroduction of the species has been attempted at a pond, but it is still on the way. The current study has summarized the causes of the extinction of A. vesiculosa in Japan, and it also aims to reduce the potential risk of extinction in extant populations of the species in the world as well as other threatened aquatic plants.

Biodiversity loss is, at present, one of the most severe global environmental issues. However, more demanding species are put at greater risk than generalists. Knowledge of the habitat requirements of threatened species is essential for defining the levels at which nature conservation efforts should prospectively operate. This study describes the habitat niche of the macrophyte species Myriophyllum alterniflorum DC., based on its occurrence along environmental gradients of sediments, flow velocity, turbidity, depth and shade on five brooks of the Upper Palatinate Forest, Bavaria. To examine the transregional validity of our results, we first carried out an analysis on the Pfreimd River and defined the outcomes as a reference. We then defined a transfer system for the other four brooks with M. alterniflorum occurrences, repeated the analysis and compared the results. We found a general pattern of preferred habitat conditions in combination with a regional aspect influencing the species distribution in each brook. We, suggest a broader formulation of habitat characteristics when aiming to describe a transregional pattern. Instead of preferences, we defined local extinction criteria for this species, namely: i) sediment with saprobic fraction, ii) stagnation of flow velocity, iii) strong turbidity iv) shading > 75% and v) water depth > 100 cm. Furthermore, we found that eutrophication is less effective under high-flow conditions. With its high demands on water quality, M. alterniflorum overlaps with the requirements of other endangered species. Therefore, conservation efforts should focus on promoting high-quality habitats, which include sustainable land management approaches at the catchment level.

Nelumbo lutea Wild. (American lotus) has a broad and changing geographical distribution that is influenced by human transplanting and changes to climate, hydrology, and habitat. Populations vary from extensive stands where the species appears to be an effective colonizer, to sites where the species has declined or appears to have been extirpated. Previous studies in apparently stable populations from central and southern United States revealed low genetic diversity within and between populations. In this study, we assess genetic diversity at the northern edge of N. lutea’s range where it is often imperiled. A total of 489 individuals in 25 populations collected in Upper Mississippi River regions in Minnesota and Wisconsin were amplified in 12 microsatellite loci. Ten microsatellite loci indicated significant deviation from Hardy-Weinberg principal and were utilized for further analysis. Generally, genetic diversity was low compared to the genetic studies from southern North America. Despite low levels of genetic differentiation (Fst range; 0.003–0.059), structure and UPGMA analysis indicated the possibility of two distinct clusters and slight admixture in some populations. Initial low genetic diversity in populations was likely caused by founder effect if few individuals were established at each site. Limited migration and clonal growth contribute to the continued low diversity. We provide recommendations and research suggestions for the conservation of this species.

Invasive aquatic plants are considered the second cause of biodiversity loss in aquatic ecosystems. Pontederia crassipes Mart., formerly Eichhornia crassipes (Mart.) Solms (water hyacinth) is one of the most dangerous invasive species in the world. Since 2006, P. crassipes has invaded Lebanon’s Al Kabir River, causing ecological and socio-economic problems. To solve them, ecological and biological characteristics are important to understand the water hyacinth response to variations in environmental conditions. The aims of this study were (i) to analyze P. crassipes growth and (ii) physico-chemical parameters at two sites and (iii) to determine ecological relationships between P. crassipes and other plant species. The main results show the existence of different cohorts of water hyacinth at the two sites. Differences in growth between these cohorts are likely due to physico-chemical differences. In addition, P. crassipes coexist with other invasive and native plants. This ecological study can help ecologists and stakeholders map invasive plants in rivers and improve their control.

The seagrass Halophila stipulacea continues to spread rapidly through the Caribbean. Documenting native herbivore use of this invasive plant is important for understanding its impacts on marine communities and the mechanisms favoring its expansion. This study used observational and experimental data to determine if juvenile green turtles (Chelonia mydas) and long-spine urchins (Diadema antillarum) from the US Virgin Islands consumed H. stipulacea in the presence of native seagrass. Juvenile turtles associated significantly more with beds of native seagrass than mixed (native and invasive), and monospecific H. stipulacea, beds or sand bottoms. When individuals were followed, turtles foraged significantly more within mixed beds, but selectively fed on native species within them and were never observed feeding on monospecific H. stipulacea stands. When offered the native Thalassia testudinum and Syringodium filiforme, along with H. stipulacea, sea urchins significantly preferred S. filiforme over the other two choices. Measurements of fourteen nutritional and chemical parameters in these three seagrasses showed strong interspecific differences, with fewer and less predictable seasonal variations. Expressing these nutritional data by wet mass, rather than dry mass, also decreased the number of significant seasonal contrasts. Despite these differences, no parameters explained low herbivore preference for the invasive seagrass satisfactorily because nutrient values of H. stipulacea were often similar to those of the preferred natives. Our results conflict with recent studies pointing at low nutritional quality aiding against herbivory and suggest other mechanisms, such as herbivore learning and recognition of a novel resource, could be more important than currently appreciated.