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  • 1
    Publication Date: 2018-03-06
    Description: Nutrient uptake by plants in nutrient-rich water in competitive conditions was investigated with two mixed culture combinations of Limnocharis flava/Pistia stratiotes and Limnocharis flava/Ipomoea aquatica by using various initial planting densities. Further, the biomass production and other growth-related parameters were measured to understand the dominant competitive behavior. The effects of interspecific competition on influencing nutrient uptake were substantial. In both experiments, the superior competitor produced a higher biomass regardless of the initial density, which was the dominant factor in determining the total nutrient uptake from water. Both aboveground competition and belowground competition appeared to be important in influencing competitive outcomes. Optimal removal of nutrients was produced by a treatment ratio of 5.31: 5.31 Limnocharis flava/Ipomoea aquatica plants/m 2 , which gave the highest observed nutrient removal, of which approximately 52% of TN removal and 90% of TP removal were due to plant uptake.
    Print ISSN: 1386-2588
    Electronic ISSN: 1573-5125
    Topics: Biology
    Published by Springer
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  • 2
    Publication Date: 2018-03-06
    Description: We tested the survival potential and fitness of two different algae strains (the diatom Thalassiosira weissflogii and the cryptophyceae Rhodomonas sp.) under different growth conditions (complete darkness and short light intervals, simulating conditions in a deep mixed water column) at different temperatures, plus the effect of these conditions on the physiological fitness and growth after re-illumination was examined. Both species survived the experimental conditions without significant cell loss or physiological damage. Two different survival strategies were observed: (1) the diatom T. weissflogii immediately reduced its metabolic rate and stopped cell division. The effect on chlorophyll a (chl- a ) content and photosynthetic capacity was negligible. At 10 °C, T. weissflogii used the short light windows to metabolize carbohydrates and growth. (2) The cryptophyte Rhodomonas sp. initially continued to grow after transfer into all trials. However, the cell number decreased after day 6. Carbohydrate and chl- a content went on to decrease dramatically (70 and 50%, respectively). After 3 days of re-illumination, T. weissflogii grew faster than of Rhodomonas sp.. The diatom seemed to benefit from better start conditions and would out-compete the cryptophyte during a spring bloom. Our results highlight that these algae groups have different strategies in dealing with darkness, which potentially endow diatoms with a competitive advantage in deep mixed waters and in the season of early spring.
    Print ISSN: 1386-2588
    Electronic ISSN: 1573-5125
    Topics: Biology
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  • 3
    Publication Date: 2018-03-06
    Description: Patterns of distribution are influenced by species environmental requirements and limits, but experimental tests are needed to discern whether correlates of abundance directly affect survival and success. Springs in Australia’s arid interior support a wide diversity of gastropods only found in springs, and these species show dichotomous patterns of distribution. “Amphibious” species are broadly distributed across many springs and microhabitats, and “aquatic” species confined to the deepest pool areas within large springs. This pattern appears to be driven by the interaction between different environmental conditions in different microhabitats and the environmental tolerances of each endemic snail species. Factorial experiments were used to test whether conditions in the environmentally extreme and variable tail area of springs (considering pH, conductivity, temperature and desiccation potential, alone and in synergistic scenarios) elicited lethal or sub-lethal responses in spring snails endemic to springs on opposite sides of the Australian arid zone. All species restricted to spring pools were able to endure 24 h exposed to the average tail conditions, alone and in combination, but most suffered mortalities when subjected to extremes, and mortalities occurred sooner in the most restricted species when elevated pH and conductivity were experienced in combination. Responses of species from different locations are similar, but pattern of distribution in the field were not correlated with tolerance of environmental extremes—with the “amphibious” species from the sub-tropics being far more sensitive than its arid counterpart. These findings suggest that environmental variance within springs can influence patterns of distribution and abundance, particularly when extremes are experienced simultaneously over sustained time periods. But despite similarities in responses across species from these two spring complexes, no simple generalisations linking distribution and tolerance were discernible.
    Print ISSN: 1386-2588
    Electronic ISSN: 1573-5125
    Topics: Biology
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  • 4
    Publication Date: 2018-03-06
    Description: A few dominant species of plants often disproportionately contribute to primary production; however, dominance has an underappreciated influence on ecosystem processes and functioning. Cascading impacts of dominant species have been documented in ecosystems undergoing eutrophication, but competitive exclusion may also influence dominance structures when limiting nutrients become scarce (i.e., in lakes experiencing oligotrophication) or with exposure to stressors to which few species are adapted (i.e., desiccation stress in wetlands). To predict impacts of widespread changes in nutrients and hydrology on dominance structures in aquatic ecosystems, we need quantitative assessments of dominance of important primary producers, including algae and cyanobacteria, which can regulate other structural and functional properties of ecosystems. We used a highly spatiotemporally resolved (7 years, 165 sites) dataset from the abundant microbial mats of the Florida Everglades to assess how and why the degree of dominance and the identity of dominant taxa vary across nutrient and desiccation gradients. Using algal counts and the dimensions of algal units (cells, coenobia, colonies, and filaments), we measured dominance as relative biovolume. As hypothesized, the relative biovolume of dominant taxa increased and the number of taxa comprising 95% of the biovolume decreased with lower concentrations of limiting nutrient in the mats (phosphorus; P) and higher desiccation stress. Algal taxa that regulate the structural integrity of mats, such as the filamentous, calcium carbonate precipitating cyanobacterium Scytonema sp., strongly influenced these patterns through their tolerance of P scarcity and desiccation. Our indicators and approach can be used to test whether dominance of microscopic primary producers, and other organisms, increases with nutrient scarcity and desiccation stress in other aquatic ecosystems.
    Print ISSN: 1386-2588
    Electronic ISSN: 1573-5125
    Topics: Biology
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  • 5
    Publication Date: 2018-03-06
    Description: Wetland seed banks comprise the propagules of plant species that have species-specific germination requirements for germination in either flooded or dry conditions. At the community level, wetland structure and succession during and after a seasonal flooding event depends upon the early life-history requirements of species, including germination under flooded and dry conditions. We examined the effects of simulated flood and post-flood scenarios on seedling emergence from a seed bank of seasonally flooded grassland in the Pantanal, Brazil. Field samplings were conducted in both wet and dry seasons, both of which were subject to flood and post-flood conditions. A total of 70 species emerged from the seed bank, dominated by Poaceae and Cyperaceae. Sixteen species were exclusive to the wet and one exclusive to the dry season. The richness of perennial species was higher under flood conditions, while the richness of annuals was greater post-flood. In general, the aquatic and amphibious species exhibited a significant germination response to flooding. Terrestrial species only germinated in post-flood conditions, with higher richness in the dry season. Four species had high seedling abundance in both treatments. The capacity of regeneration by seeds is high in these grasslands and can be increased by seasonal flooding and drawdown. In these seasonally flooded grasslands, we observed three main germination strategies: under flooded conditions, aquatic and amphibious species; post-flood conditions, an explosion of annual amphibious and terrestrial species; and in moist soil, perennial terrestrial species. The differential responses to flooding versus post-flood conditions help to maintain the structure and species richness in the community over time.
    Print ISSN: 1386-2588
    Electronic ISSN: 1573-5125
    Topics: Biology
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  • 6
    Publication Date: 2018-03-06
    Description: Determination of ecological responses to river flows is fundamental to understanding how flow-dependent ecosystems have been altered by regulation, water diversions and climate change, and how to effect river restoration. Knowledge of ecohydrological relationships can support water management and policy, but this is not always the case. Management rules have tended to be developed ahead of scientific knowledge. The lag between practice and knowledge could be addressed by using historical monitoring data on ecological responses to changes in flows to determine significant empirical ecohydrological relationships, as an adjunct to investigating responses prospectively. This possibility was explored in the Murray–Darling Basin, Australia. We assessed 359 data sets collected during monitoring programs across the basin. Of these, only 32 (9%) were considered useful, based on a match between the scale at which sampling was done and ecological responses are likely to occur, and used to test flow–ecology predictions for phytoplankton, macroinvertebrates, fishes, waterbirds, floodplain trees, basin-scale vegetation and estuarine biota. We found relationships between flow and ecological responses were likely to be more strongly supported for large, long-lived, widespread biota (waterbirds, basin-scale vegetation, native fishes), than for more narrowly distributed (e.g. estuarine fishes) or smaller, short-lived organisms (e.g. phytoplankton, macroinvertebrates). This pattern is attributed to a mismatch between the design of monitoring programs and the response time frames of individual biota and processes, and to the use of local river discharge as a primary predictor variable when, for many biotic groups, other predictors need to be considered.
    Print ISSN: 1386-2588
    Electronic ISSN: 1573-5125
    Topics: Biology
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  • 7
    Publication Date: 2018-03-06
    Description: Invasions of introduced plants are considered among the greatest threats to biodiversity worldwide. Aquatic habitats suffer invasion more frequently and extensively than do terrestrial habitats. Although the role of roots in plant anchoring and support is important, previous studies have focused much attention on the morphological traits of above-ground parts, with relatively less attention given to the root structures of aquatic plants. In this study, we aimed to compare differences in root morphological and structural traits between introduced and native plants in response to different substrates. We hypothesized that introduced aquatic plants have an advantage over native plants with regard to root trait values and plasticity. A total of six aquatic plants were used: Two invasive and one exotic noninvasive species were paired with their native counterparts according to life form (amphibious emergent, submerged and floating-leaved) and cultivated in substrates of clay, a clay/sand mixture ( v : v  = 1:1) or sand. Root morphological traits, topological indices and root relative distance plasticity indices were quantified. The results indicated that different substrates have various effects on the root traits of these six aquatic plants; the introduced plants generally exhibited higher plasticity than did their native counterparts of the same life form.
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    Electronic ISSN: 1573-5125
    Topics: Biology
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  • 8
    Publication Date: 2018-03-06
    Description: The replacement of native forests by pastures takes place widely in the Andes. The effects of such land-use change on aquatic assemblages are poorly understood. We conducted a comparative analysis of the effects of forest conversion to pastures on the taxonomic, structural, and functional composition of macroinvertebrates (benthic and leaf-associated) in montane and upper montane streams (ecosystem type) of the south Ecuadorian Andes. Taxonomic composition of benthic and leaf-associated macroinvertebrates was different between ecosystem type and land use. Also, major differences in the structural and functional composition of benthic and leaf-associated macroinvertebrates were mainly promoted by land use in both ecosystem types. Forested streams showed higher diversity than pasture streams, sustaining more shredder, scraper, and predatory invertebrates. We also observed differences in the macroinvertebrate communities between benthic and leaf-bag samples. Leaf bags had lower diversity and more collector invertebrates than benthic samples. This study highlights the large effect of riparian forest conversion to pasture land on macroinvertebrate communities, and the importance of using appropriate sampling techniques to characterize aquatic assemblages. We also recommend the maintenance and restoration of riparian vegetation to mitigate the effects of deforestation on stream communities and ecosystem processes.
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    Electronic ISSN: 1573-5125
    Topics: Biology
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  • 9
    Publication Date: 2018-03-06
    Description: Algal biofuel has potential as a source of renewable fuel and a tool for wastewater remediation. Open algal bioreactors fertilized with wastewater can have net energy gain but are vulnerable to colonization by algal grazers. However, colonizing predaceous insects may limit grazer impacts on algae. Here, we investigate the effects of grazers, predators, and invading algae species on algal production and community structure in high-nutrient environments. First, we grew diverse algal assemblages in treated municipal wastewater in a greenhouse with Daphnia grazers and different insect predators that were added experimentally. When Daphnia were present without predators, they eliminated suspended algae. But, dragonfly larvae [Odonata: Libellulidae] and backswimmers [Hemiptera: Notonectidae], but not larval diving beetles [Coloeoptera: Dytiscidae], suppressed Daphnia allowing suspended algae to persist. Second, we grew Chlorella algae in field tanks that were open or protected from natural invertebrate colonization and half the tanks received wild-collected plankton in a factorial design. Mosquito larvae [ Culex sp.] readily colonized open tanks and reduced algal mass and dissolved phosphorus concentrations. Colonist addition to open tanks shifted algal functional and taxonomic composition but did not impact suspended algal production. Our study indicates that large numbers of grazer individuals can rapidly colonize open bioreactors. Experimentally added and naturally colonizing grazers altered algal community structure and reduced algal standing crops but may also aid in nutrient removal from wastewater-fed bioreactors. Effective operation of open algal bioreactors must consider cultivated algae species’ vulnerability to competition and local grazers as well as the ability of potential predators to both naturally disperse into bioreactors and to control grazers.
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    Topics: Biology
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  • 10
    Publication Date: 2018-03-06
    Description: We examined spatial and environmental effects on the deconstructed assemblages of littoral macroinvertebrates within a large lake. We deconstructed assemblages by three biological trait groups: body size, dispersal mode and oviposition behaviour. We expected that spatial effects on assemblage structuring decrease and environmental effects increase with increasing body size. We also expected stronger environmental filtering and weaker spatial effect on the assemblages of flying species compared with assemblages of non-flying species. Stronger effect of environmental filtering was expected on the assemblages with species attaching eggs compared with assemblages of species with free eggs. We used redundancy analysis with variation partitioning to examine spatial and environmental effects on the deconstructed assemblages. As expected, the importance of environmental filtering increased and that of spatial effects decreased with increasing body size. Opposite to our expectations, assemblages of non-flying species were more affected by environmental conditions compared to assemblages of flying species. Concurring with our expectations, the importance of environmental filtering was higher in structuring assemblages of species attaching eggs than in structuring those with freely laid eggs. The amount of unexplained variation was higher for assemblages with small-sized to medium-sized species, flying species and species with free eggs than those with large-sized species, non-flying species and species with attached eggs. Our observations of decreasing spatial and increasing environmental effects with increasing body size of assemblages deviated from the results of previous studies. These results suggest differing metacommunity dynamics between within-lake and among-lake levels and between studies covering contrasting taxonomic groups and body size ranges.
    Print ISSN: 1386-2588
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    Topics: Biology
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