Response of invasive macrophyte species to drawdown: The case of Elodea sp.

The response to drawdown of vegetative fragments (whole plants, shoot fragments and turions) of two invasive macrophyte species, Elodea canadensis and Elodea nuttallii, was studied through laboratory experiments. In addition, field observations were made on the colonisation of a wetland by E. nuttallii before and after a natural drawdown. The survival and the growth of vegetative fragments of E. nuttallii were higher than those of E. canadensis after an artificial drawdown of several days. In the field the recolonisation by E. nuttallii of a wetland that was drained for 10 weeks during a summer drawdown was very rapid, the abundance of this macrophyte species being not affected by the drawdown event. We conclude that E. nuttallii possesses a high resilience to desiccation and that a summer drawdown would not be efficient in the control of this invasive species.     

Responses of two invasive macrophyte species to salt

Aquatic ecosystems are particularly sensitive to the introduction of species due to human activities. Increasing salinity in freshwaters due to sea intrusion or to human activities (road salt, industry, etc.) is known to have a negative impact on aquatic organisms and could play a role in the dynamics of invaders. This study compares salt tolerance levels of two introduced aquatic plants Myriophyllum aquaticum (Velloso) Verdcourt and Ludwigia grandiflora (Michaux) Greuter and Burdet. Plants were collected in spring, summer and autumn 2010, and were exposed to a range of salt concentrations (1, 3 and 6 g/L). Plant growth was determined by measuring seven morphological traits and their photosynthetic activity. Increased salt levels induced a decline in growth and photosynthetic activity in L. grandiflora, while photosynthetic activity in M. aquaticum remained constant at all salt concentrations. The response of both species to salt varied according to the season. M. aquaticum allocated its energy to growth in autumn, whereas the growth of L. grandiflora remained constant whatever the season. Our results suggested that M. aquaticum stimulated root and leaf production at the end of summer, which conferred resistance to salt stress and allowed this species to become invasive by overcompensating for this stress. Conversely, L. grandiflora induced premature senescence and lost its leaves. In the context of worldwide salinisation of freshwaters, M. aquaticum could colonize brackish water and other water bodies, whereas L. grandiflora invasion could be limited.     

Experiments on growth interactions between two invasive macrophyte species

Abstract. The success of invasive species has been attributed to the ability to displace other species by direct competition. We studied growth and possible competition between the two macrophyte species Elodea nuttallii and E. canadensis, because the former has been observed to replace the latter in the field. Additional experiments were conducted in aquaria with mixed plantings of Elodea species. Species growth was measured and competitive abilities of each species determined by applying the reciprocal yield model to mean plant weight and length. In monocultures the growth rates of the two species were similar, while in mixtures the growth rate of E. canadensis was significantly lower than that of E. nuttallii. E. canadensis was more sensitive to intraspecific than to interspecific neighbours, whereas E. nuttallii was indifferent to the presence of neighbours. Differential growth characteristics of Elodea species can explain the displacement of E. canadensis by E. nuttallii under eutrophic field conditions.     

Comparative studies of the photosynthesis of the submerged macrophyte Elodea canadensis and the filamentous algae Cladophora glomerata and Spirogyra sp.

The photosynthetic and respiratory responses of Elodea canadensis Michx., Cladophora glomerata (L.) Kütz. and Spirogyra sp. to oxygen, temperature, HCO₃⁻¹ concentration, pH and irradiance were determined. Photosynthesis was inhibited by O₂ in all three species under all conditions and inhibition was greatert in E. canadensis. This inhibition was not caused solely by an accelerated rate of dark respiration and this suggests that photorespiration may be an important factor controlling productivity, particularly in E. canadensis.Photosynthetic performance was impaired much more in E. canadensis than in either of the filamentous algae conditions of high pH and low CO₂ concentrations. In the field photosynthesis of these algae may increase the pH and reduce the CO₂ content of the water sufficiently to exert deleterious effects on macrophyte photosynthesis. Such a plant-induced change in water quality could give C. glomerata a competitive advantage over E. canadensis and be a factor in the replacement of the vascular plant by the alga in some waters.     

Plasticity responses of an invasive macrophyte species to inorganic carbon availability and to the interaction with a native species

The acorn barnacle Perforatus perforatus has a defined breeding temperature range and reproductive season that varies geographically. This study aims to investigate the influence of reproductive parameters of P. perforatus in species distribution ranges in the NE Atlantic. The hypothesis tested is that the breeding season of P. perforatus off NW Portugal begins earlier and is longer than at the northern distribution limit of this species, and that fecundity is higher in terms of number of broods per individual per breeding season. The span of the breeding season and fecundity indices were assessed based on the presence and maturation of ovigerous lamellae and correlated with temperature. Results showed that the breeding season in the NW Portuguese coast lasts over 10 months (February–November) and the number of broods was determined to be 9.2 ind/year. Temperature seems to be a primary factor determining the breeding season, but other factors, such as food availably, light and photoperiod, are also of great importance. However, the higher quantity of embryos produced in NW Portugal is not reflected in a higher abundance of settled adults in rocky shores. Contrarily, the species is particularly abundant in artificial substrata offshore.     

Cumulative consumption of the lake macrophyte Elodea by abundant generalist invertebrate herbivores

Previous investigations have shown that macrophyte biomass can be substantially reduced by invertebrate herbivores but have not provided evidence for the links between the magnitude of the observed damage and the densities of herbivores. The results of this study support the hypothesis that the abundant occurrence of the epiphytic generalist herbivores may result in their cumulative consumption which, in turn, can be regarded as the mechanism responsible for often observed relatively high level of herbivory on freshwater macrophytes. The percentage of Elodea sp. biomass consumed by invertebrates was estimated for six European lakes, based on analysis of gut contents, daily rations and the density of epiphytic herbivores. Although the daily ration of these invertebrates when feeding upon Elodea averaged only 14.6% of their dry mass, their biomass was relatively high (from 0.163 to 1.161 g DW per 100 g DW plant). The estimated percentage of Elodea biomass consumed during one summer month by epiphytic invertebrates ranged from 0.5 to 5.9%. These values, after extrapolating to the whole growing season would mean that the biomass of Elodea lost to herbivory was between about 2 and 23%, an estimate which are within the range of consumption reported by other authors.     

The influence of environmental factors on apparent photosynthesis and respiration of the submersed macrophyte Elodea canadensis

Abstract Oxygen effects on apparent photosynthetic and dark respiratory O₂ exchange rates of detached leaves of Elodea canadensis Michx. (Hydrocharitaceae) were determined over a range of conditions which the submersed plant is likely to experience in shallow water. Apparent photosynthesis is inhibited by O₂ under all the experimental regimes of light, temperature, CO₂ concentration and pH. This inhibition is not caused solely by an accelerated rate of dark respiration, and the observed variations in O₂ inhibition are comparable to O₂ effects on photosynthesis and photorespiration of terrestrial C₃ plants. Percentage inhibition of apparent photosynthesis is enhanced by high O₂ and also by low CO₂. These results indicate that high O₂, high pH and low CO₂ conditions could cause major losses in photosynthetic activity under field conditions. This may account for some of the losses in biomass that are observed under still water conditions.     

Bradyrhizobium xenonodulans sp. nov. isolated from nodules of Australian Acacia species invasive to South Africa

A genealogical concordance approach was used to delineate strains isolated from Acacia dealbata and Acacia mearnsii root nodules in South Africa. These isolates form part of Bradyrhizobium based on 16S rRNA sequence similarity. Phylogenetic analysis of six housekeeping genes (atpD, dnaK, glnII, gyrB, recA and rpoB) confirmed that these isolates represent a novel species, while pairwise average nucleotide identity (ANIb) calculations with the closest type strains (B. cosmicum 58S1^T, B. betae PL7HG1^T, B. ganzhouense CCBAU 51670 ^T, B. cytisi CTAW11^T and B. rifense CTAW71^T) resulted in values well below 95–96%. We further performed phenotypic tests which revealed that there are high levels of intraspecies variation, while an additional analysis of the nodA and nifD loci indicated that the symbiotic loci of the strains are closely related to those of Bradyrhizobium isolates with an Australian origin. Strain 14AB^T (=LMG 31415 ^T = SARCC-753 ^T) is designated as the type strain of the novel species for which we propose the name Bradyrhizobium xenonodulans sp. nov.     

The threat of invasive species to bats: a review

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The prediction of macrophyte species occurrence in Swiss ponds

The study attempted to model the abundance of aquatic plant species recorded in a range of ponds in Switzerland. A stratified sample of 80 ponds, distributed all over the country, provided input data for model development. Of the 154 species recorded, 45 were selected for modelling. A total of 14 environmental parameters were preselected as candidate explanatory variables. Two types of statistical tools were used to explore the data and to develop the predictive models: linear regression (LR) and generalized additive models (GAMs). Six LR species models had a reasonable predictive ability (30–50% of variance explained by the selected predictors). There was a gradient in the quality of the 45 GAM models. Ten species models exhibited both a good fit and statistical robustness: Lemna minor, Phragmites australis, Lysimachia vulgaris, Galium palustre, Lysimachia nummularia, Iris pseudacorus, Lythrum salicaria, Lycopus europaeus, Phalaris arundinacea, Alisma plantago-aquatica, Schoenoplectus lacustris, Carex nigra. Altitude appeared to be a key explanatory variable in most of the species models. In some cases, the degree to which the shore was shaded, connectivity between water bodies, pond area, mineral nitrogen levels, pond age, pond depth, and the extent of agriculture or pasture in the catchment were selected as additional explanatory variables. The species models demonstrated that it is possible to predict species abundance of aquatic macrophytes and that each species responded individually to distinct environmental variables.     

Long‐term allelopathic control of phytoplankton by the submerged macrophyte Elodea nuttallii

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Modelling spread of the invasive macrophyte Cabomba caroliniana

1. Predicting spread of non-indigenous species requires an understanding of where propagules are being transported, and whether these propagules can survive in the novel habitat and successfully integrate into the recipient community. In this study, we model potential spread of invading Cabomba caroliniana in Ontario, Canada, using a combination of passive and active dispersal models coupled with an environmental suitability model, thereby considering the first two stages of the invasion process.
2. Measures of propagule pressure incorporated both human-mediated dispersal via trailered boats, and advective flow from invaded to non-invaded systems, while habitat suitability was forecasted by combining native and global data sets and using boosted regression trees.
3. Risk of invasion differed depending on the combination of approaches used and the time period considered. Three lakes appear to be at greatest risk owing to a combination of high boater and water movement from invaded sources, and high environmental suitability. The best predictors of lake suitability were pH, mean lake temperature and dissolved calcium concentration. Hundreds of lakes in Ontario may be suitable for establishment of Cabomba , highlighting the need for vector management.     

Achieving effective outreach for invasive species: firewood case studies from 2005 to 2016

Invasive forest pests are damaging North American forests, and their intracontinental spread can be accelerated through the movement of infested firewood. We assessed the general public’s awareness, attitudes, and perceptions of forest health issues and identified potential strategies for more effective delivery of information about invasive forest pests and firewood transport. We analyzed data obtained from five surveys conducted between 2005 and 2016 (n?=?4,840). Awareness, choice of mode of information, and trusted messenger were predicted using linear regression models based on selected independent variables including age, race, gender, education level, and the participant’s type of residential area. Overall, awareness regarding invasive forest pests was low among participants. Participants stated they would be most likely to pay attention to a flyer handed out when entering a state or national park or receiving an email after making a campsite reservation. State forestry agencies were the most believable source of information regarding forest health issues. For the modes of information listed on the survey, older participants and those with higher education levels were more likely to have greater awareness levels and to pay attention, while female and younger participants were more likely to indicate they believed the messengers. We conclude that awareness is key for modifying behavior related to firewood transport; as such, educational campaigns with effective messaging strategies could be a successful approach to reducing the movement of firewood by members of the public.

     

The immediate and long‐term effects of water drawdown on macrophyte assemblages in a large subtropical reservoir

1. Disturbances play a central role in determining the spatial and temporal dynamics of many plant communities. In our study of macrophyte assemblages at 150 sites in five arms of a large subtropical reservoir (Itaipu Reservoir, Brazil–Paraguay border), we used co‐occurrence null models and spatiotemporal analyses to describe the patterns in the assemblages during a historically large water drawdown in 2000, in comparison with the previous year (1999) and subsequent years (2001–07). A C‐Score co‐occurrence index tested the null hypothesis of random structure during the drawdown period. A detrended correspondence analysis and multiresponse permutation procedure were used to verify whether species composition differed before, during and after the disturbance. 2. In contrast to our expectations, the null models showed that the macrophyte assemblages were spatially structured during the drawdown (2000), although species composition was significantly different from the previous year (1999) and also changed in the following years (2001–07). Significant species co‐occurrence patterns were generated by the drawdown disturbance, with species extinctions and colonisation by new species from propagules and seed bank germination. 3. The randomness we expected in 2000 actually occurred in 2001, probably because the reestablishment of normal water level enabled both submersed and free‐floating species to recolonise the shore that emergent species had inhabited since the drawdown. Biotic interactions appeared to increase during the years after the disturbance and the habitat preferences of the aquatic macrophytes were re‐established, resulting in higher similarities in aquatic macrophyte species composition in the years after the drawdown.     

Altered stream-flow regimes and invasive plant species: the Tamarix case

Aim  To test the hypothesis that anthropogenic alteration of stream-flow regimes is a key driver of compositional shifts from native to introduced riparian plant species.
Location  The arid south-western United States; 24 river reaches in the Gila and Lower Colorado drainage basins of Arizona.
Methods  We compared the abundance of three dominant woody riparian taxa (native Populus fremontii and Salix gooddingii , and introduced Tamarix ) between river reaches that varied in stream-flow permanence (perennial vs. intermittent), presence or absence of an upstream flow-regulating dam, and presence or absence of municipal effluent as a stream water source.
Results  Populus and Salix were the dominant pioneer trees along the reaches with perennial flow and a natural flood regime. In contrast, Tamarix had high abundance (patch area and basal area) along reaches with intermittent stream flows (caused by natural and cultural factors), as well as those with dam-regulated flows.
Main conclusions  Stream-flow regimes are strong determinants of riparian vegetation structure, and hydrological alterations can drive dominance shifts to introduced species that have an adaptive suite of traits. Deep alluvial groundwater on intermittent rivers favours the deep-rooted, stress-adapted Tamarix over the shallower-rooted and more competitive Populus and Salix . On flow-regulated rivers, shifts in flood timing favour the reproductively opportunistic Tamarix over Populus and Salix , both of which have narrow germination windows . The prevailing hydrological conditions thus favour a new dominant pioneer species in the riparian corridors of the American Southwest. These results reaffirm the importance of reinstating stream-flow regimes (inclusive of groundwater flows) for re-establishing the native pioneer trees as the dominant forest type.     

The contribution of passive surveillance to invasive species management

It has been recognised for some time that the community has an important role to play in invasive-species management. Reports from the community about new incursions can lead to significant cost savings when this early detection results in shorter management programs. Unfortunately there is little to guide invasive-species managers on cost-effective ways to elicit and incorporate information from the public in their pest-management programs. Not all community surveillance is equal: some information from the public about the presence of pests and diseases may arise from chance encounters, other data may be reported by stakeholders from a particular industry or by groups of volunteers organised on the basis of citizen science activities. While the resources, activities and effort required to encourage each type of community surveillance are known to differ, very little is known of the relationships that determine effectiveness, and thus the appropriate level of investment that would be required to encourage a particular level of reporting. In this research we focus on passive surveillance—the most fortuitous type of community surveillance—and review the current knowledge base on measuring its cost and effectiveness. We aim to stimulate the research required to improve our understanding of passive surveillance, and we provide guidance on the type of data that should be collected by agencies to enable this research. This information could then provide us with the ability to design optimal surveillance portfolios that integrate the surveillance opportunities provided by the public to best advantage.     

An invasive macrophyte alters sediment chemistry due to suppression of a native isoetid

The submersed macrophyte Utricularia inflata (inflated bladderwort) is a recent invader of Adirondack Mountain lakes (NY, USA). A 15-week greenhouse experiment and a 7-week field experiment were conducted to test the hypothesis that this rootless species fundamentally changes sediment chemistry through its suppression of the native short-statured species, Eriocaulon aquaticum. E. aquaticum has an extensive root system that releases oxygen into the sediment. In greenhouse conditions, E. aquaticum raised the porewater redox potential of otherwise bare sediment from 25 to 324 mV, lowered the sediment porewater pH from 5.7 to 4.6, and depleted the dissolved inorganic carbon and ammonium concentrations in the sediment porewater by 68.4 and 96.0%, respectively (P<0.001 for all four parameters). A cover of U. inflata over E. aquaticum, however, greatly reduced the latter’s effect on redox potential (P<0.001), dissolved solutes (P<0.001), and pH (P<0.05). E. aquaticum biomass increased during the greenhouse experiment in the absence of U. inflata, but decreased in its presence (P<0.001). Redox and growth rate results from the field experiment paralleled those from the greenhouse experiment. Our data suggest that U. inflata may change nutrient cycling in Adirondack lake ecosystems by reducing the growth of native isoetid macrophytes, such as E. aquaticum, and consequently altering key features of sediment chemistry.     

Response ofWestiellopsis prolifica andAnabaena sp. to salt stress

Summary The response of a salt-tolerantWestiellopsis prolifica ARM 366 and a sensitiveAnabaena C-10 to NaCl was studied. While the former could tolerate up to 400mm NaCl, the latter was highly sensitive to concentrations above 50mm NaCl. Under salt stress, the tolerantW. prolifica showed an increased nitrogen demand as exemplified by high nitrogenase activity, and growth inhibition at higher concentrations of NaCl did not appear to be a direct consequence of inhibition of nitrogen fixation. One of the striking responses to Na⁺ challenge by the tolerantW. prolifica was the excess production of extracellular polysaccharides which adsorbed the bulk of the Na⁺. The influx of Na⁺ into the cell was comparatively small.

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Resumen Se estudió la respuesta al NaCl deWestiellopsis prolifica ARM 366, organismo tolerante a la sal, y deAnabaena C-10 que es sensible. El primero pudo tolerar concentraciones de hasta 400mm NaCl, sin embargo Anabaena C-10 se mostró extremadament sensible a concentraciones superiores a 50mm de NaCl. Bajo condiciones de estrés salinoW. prolifica mostró un incremento en la demanda de N₂, como se deduce de la elevada actividad nitrogenásica; la inhibición del crecimiento a concentraciones superiores de NaCl no se pudo relacionar directamente con la inhibición de la fijación de nitrógeno. Una de las respuestas más sorprendentes deW. prolifica frente al Na⁺ fue la producción de un exceso de polisaccaridos extracelulares que absorbieron gran parte del Na⁺. El flujo de Na⁺ hacia la célula fue, pues, comparativemente pequeño.

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Résumé On a étudié la réponse au NaCl d'une souche halo-tolérante deWestiellopsis prolifica (ARM 366) et, d'une souche halo-sensible d'Anabaena (C-10). Alors que la première tolère jusqu'a 400mm NaCl, la seconde est hautement sensible aux concentrations supérieures à 50mm. Soumise à un choc de salinité, la souche halo-tolérante deW. prolifica présente une demande d'azote accrue, comme le montre une activité nitrogénase élevée, et l'inhibition de la croissance par une forte concentration en NaCl ne parait pas être la conséquence directe d'une inhibition de la fixation d'azote. Une réponse remarquable deW. prolifica à l'agression par Na⁺ est la production en excès de polysaccharides exo-cellulaires, qui absorbent la plus grande partie du Na⁺. La pénétration de Na⁺ dans la cellule est relativement faible.

     

Wetland macrophyte diversity, trophic status and phytoplankton： a case study of the cascading effects of an invasive herbivore

Shallow water bodies can exist in alternative stable states, a clear water state with high coverage of macrophytes or a turbid state with high phytoplankton biomass. The alternative equilibria hypothesis has been proposed to explain the occurrence of the alternative stable states (Scheffer et al., 1993)[1], which assumes that: 1),