Responses of three invasive alien aquatic plant species to climate warming and plant density.

Climate warming may impact plant invasion success directly, as well as indirectly through changes among interactions within plant communities. However, the responses of invasive alien aquatic species to plant density and rising temperatures remain largely unknown. We tested the effects of plant density and neighbour plant identity at different temperatures to better understand the performance of a community of invasive species exposed to climate warming. A microcosm experiment was conducted with three invasive aquatic plants species-Elodea canadensis, Egeria densa and Lagarosiphon major-, at mono and polycultures with low and high plant density, at 16 °C, 19 °C and 23 °C. The results clearly demonstrated that rising temperature influenced, either as a single parameter or as a combined factor, at least one of the measured traits of the three invasive species. Leaf area of E. densa, root number of L. major and growth of E. densa and L. major were influenced by temperature, plant density and neighbour identity. Plant density influenced all traits with the exception of leaf area of E. canadensis and lateral branch production of E. densa. Neighbour identity had no effect on growth rate and leaf area of E. canadensis, on lateral branch and roots production of E. densa and on leaf area of L. major. These findings establish that rising temperature could enhance competition or facilitation among E. canadensis, L. major and E. densa and could cancel the beneficial effects of the presence of a neighbour species; however, the magnitude of this effect was strongly dependent on plant density. Rising temperature due to climate change will likely play a crucial role in interactions between invasive species within plant communities and in the further spread of these invasive aquatic plants.

An efficient Egeria najas-derived biochar supported nZVI composite for Cr(VI) removal: Characterization and mechanism investigation based on visual MINTEQ model.

Egeria najas is a submerged aquatic plant, and the literatures on resourcification of submerged aquatic plant biochar remain limited. Until now, there has been no study on submerged aquatic plant biochar supported nZVI that is widely applied for removal of diversified contaminants in solution. In this study, an efficient approach to the preparation of Egeria najas-derived biochar supported nZVI composite is first developed for Cr(VI) removal in wastewater. The adsorption behavior and mechanism of Cr(VI) removal on the as-prepared Egeria najas-derived biochar/nZVI (EN@nZVI) composite were investigated. The results of FTIR and XPS indicate that the EN@nZVI surface had many functional groups such as R-COOH, R-OH, R-NH2 and R-C-O-C, etc, which could provide active sites during the adsorption process. The BET results showed that the EN@nZVI had large specific surface area and average pore, which were 142.49 m2/g and 9.85 nm, respectively. EN@nZVI demonstrated high reactivity for Cr(VI) removal. Compared with nZVI, Cr(VI) removal efficiency by EN@nZVI is 50% higher than that of nZVI within 0.5 h. Furthermore, the maximum adsorption capacity of Cr (VI) was 56.79 mg/g and the energy of activation (Ea) was 31.30 kJ/mol. The adsorption process was well described by the pseudo-second order model and Sips adsorption isotherm model. The reaction mechanism of Cr(VI) removal was a multi-step removal mechanism, involving adsorption, surface complex formation, reduction and ion exchange reaction.

Engineered nanoparticles interact with nutrients to intensify eutrophication in a wetland ecosystem experiment.

Despite the rapid rise in diversity and quantities of engineered nanomaterials produced, the impacts of these emerging contaminants on the structure and function of ecosystems have received little attention from ecologists. Moreover, little is known about how manufactured nanomaterials may interact with nutrient pollution in altering ecosystem productivity, despite the recognition that eutrophication is the primary water quality issue in freshwater ecosystems worldwide. In this study, we asked two main questions: (1) To what extent do manufactured nanoparticles affect the biomass and productivity of primary producers in wetland ecosystems? (2) How are these impacts mediated by nutrient pollution? To address these questions, we examined the impacts of a citrate-coated gold nanoparticle (AuNPs) and of a commercial pesticide containing Cu(OH)2 nanoparticles (CuNPs) on aquatic primary producers under both ambient and enriched nutrient conditions. Wetland mesocosms were exposed repeatedly with low concentrations of nanoparticles and nutrients over the course of a 9-month experiment in an effort to replicate realistic field exposure scenarios. In the absence of nutrient enrichment, there were no persistent effects of AuNPs or CuNPs on primary producers or ecosystem productivity. However, when combined with nutrient enrichment, both NPs intensified eutrophication. When either of these NPs were added in combination with nutrients, algal blooms persisted for >50 d longer than in the nutrient-only treatment. In the AuNP treatment, this shift from clear waters to turbid waters led to large declines in both macrophyte growth and rates of ecosystem gross primary productivity (average reduction of 52% ± 6% and 92% ± 5%, respectively) during the summer. Our results suggest that nutrient status greatly influences the ecosystem-scale impact of two emerging contaminants and that synthetic chemicals may be playing an under-appreciated role in the global trends of increasing eutrophication. We provide evidence here that chronic exposure to Au and Cu(OH)2 nanoparticles at low concentrations can intensify eutrophication of wetlands and promote the occurrence of algal blooms.

Occurrence of complex type free N-glycans with a single GlcNAc residue at the reducing termini in the fresh-water plant, Egeria densa.

In our previous study, we found unique free N-glycans (FNGs), which carry a single GlcNAc residue (GN1) at the reducing-end side and the Lewis-a epitope at the non-reducing-end side, in the culture broth of rice cells. Based on the FNG structural features and the substrate specificity of plant ENGase, we hypothesized that there might be a novel biosynthetic mechanism responsible for the production of these unique GN1-FNGs, in which high-mannose type (HMT)-GN1-FNGs produced in the cytosol from misfolded glycoproteins by ENGase are transported back into the endoplasmic reticulum and processed to plant complex type (PCT)-GN1-FNGs in the Golgi apparatus. Until now, however, PCT-GN1-FNGs had only been found in the culture broth of rice cultured cells and never in plants, suggesting that the formation of PCT-GN1-FNGs might be generated under special or artificial conditions. In this study, we confirm the presence of PCT-GN1-FNGs, HMT-GN1-FNGs and PCT-GN2-FNGs in the fresh-water plant Egeria densa. These results suggest that a mechanism responsible for the production of PCT-GN1-FNG is present in native plant tissues.

A lysigenic programmed cell death-dependent process shapes schizogenously formed aerenchyma in the stems of the waterweed Egeria densa.

BACKGROUND AND AIMS: Plant adaptation to submergence can include the formation of prominent aerenchyma to facilitate gas exchange. The aim of this study was to characterize the differentiation of the constitutive aerenchyma in the stem of the aquatic macrophyte Egeria densa (Hydrocharitaceae) and to verify if any form of cell death might be involved. METHODS: Plants were collected from a pool in a botanical garden. Aerenchyma differentiation and apoptotic hallmarks were investigated by light microscopy and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) assay coupled with genomic DNA extraction and gel electrophoresis (DNA laddering assay). Cell viability and the occurrence of peroxides and nitric oxide (NO) were determined histochemically using specific fluorogenic probes. KEY RESULTS: Aerenchyma differentiation started from a hexagonally packed pre-aerenchymatic tissue and, following a basipetal and centripetal developmental pattern, produced a honeycomb arrangement. After an early schizogenous differentiation process, a late lysigenous programmed cell death- (PCD) dependent mechanism occurred. This was characterized by a number of typical apoptotic hallmarks, including DNA fragmentation, chromatin condensation, apoptotic-like bodies, partial cell wall lysis and plasmolysis. In addition, local increases in H2O2 and NO were observed and quantified. CONCLUSIONS: The differentiation of cortical aerenchyma in the stem of E. densa is a complex process, consisting of a combination of an early schizogenous differentiation mechanism and a late lysigenous PCD-dependent process. The PCD remodels the architecture of the gas spaces previously formed schizogenously, and also results in a reduction of O2-consuming cells and in recycling of material derived from the lysigenic dismantling of the cells.

Red light mitigates Cd toxicity in Egeria densa by restricting Cd accumulation and modulating antioxidant defense system.

Controlling light qualities have been acknowledged as an effective method to enhance the efficiency of phytoremediation, as light has a significant impact on plant growth. This study examined the effects of light qualities on cadmium (Cd) tolerance in aquatic plant Egeria densa using a combination of biochemical and transcriptomic approaches. The study revealed that E. densa exhibits higher resistance to Cd toxicity under red light (R) compared to blue light (B), as evidenced by a significant decrease in photosynthetic inhibition and damage to organelle ultrastructure. After Cd exposure, there was a significantly reduced Cd accumulation and enhanced levels of both glutathione reductase (GR) activity and glutathione (GSH), along with an increase in jasmonic acid (JA) in R-grown E. densa compared to B. Transcriptional analysis revealed that R caused an up-regulation of Cd transporter genes such as ABCG (G-type ATP-binding cassette transporter), ABCC (C-type ATP-binding cassette transporter), and CAX2 (Cation/H+ exchanger 2), while down-regulated the expression of HIPP26 (Heavy metal-associated isoprenylated plant protein 26), resulting in reduced Cd uptake and enhanced Cd exportation and sequestration into vacuoles. Moreover, the expression of genes involved in phytochromes and JA synthesis was up-regulated in Cd treated E. densa under R. In summary, the results suggest that R could limit Cd accumulation and improve antioxidant defense to mitigate Cd toxicity in E. densa, which might be attributed to the enhanced JA and phytochromes. This study provides a foundation for using light control methods with aquatic macrophytes to remediate heavy metal contamination in aquatic systems.

Red light alleviates Cd toxicity in Egeria densa by modifying carbon-nitrogen metabolism and boosting energy metabolism.

Among the various pollutants detected in aquatic ecosystems, cadmium (Cd) is considered as one of the most hazardous. Freshwater macrophytes have been recognized as possible candidates for eliminating Cd from environment. Nevertheless, the impact of light quality on their ability to tolerate Cd toxicity remains unclear, and the underlying mechanisms have yet to be fully elucidated. In this study, we utilized physiological testing and metabolomics to explore the potential mechanisms by which light quality influences the ability of Egeria densa, a significant Cd hyperaccumulator, to withstand Cd toxicity. The study demonstrated that following Cd treatment, E. densa grown under red light exhibited superior photosynthetic efficiency compared to those grown under blue light, as evidenced by significantly increased photosynthetic rate, higher starch content, and greater activity of photosynthetic enzymes. Moreover, metabolomic analyses revealed that under Cd stress, E. densa grown under red light exhibited an enhanced glycolysis for increased energy production. Sucrose metabolism was also improved to generate sufficient sugar including glucose, fructose and mannose for osmotic adjustment. Moreover, under red light, the heightened production of α-ketoglutarate via tricarboxylic acid (TCA) cycle redirected nitrogen flow towards the synthesis of resilient substances such as γ-Aminobutyric Acid (GABA) and methionine. The production of these substances was ∼2.0 and 1.3 times greater than that of treatment with Cd under blue light, thereby improving E. densa's capacity to withstand Cd stress. This study represents the initial investigation into the possible mechanisms by which light quality influences the ability of E. densa to withstand Cd toxicity through regulating CN metabolism. Furthermore, these findings have the potential to improve phytoremediation strategies aimed at reducing Cd pollution.

Effect of acid solutions on plants studied by the optical beam deflection method.

The optical beam deflection method was applied to study the effects of acid solution on both a terrestial and aquatic plants Egeria and Cerastium, which are common aquatic plant and terrestial weed respectively. A probe beam from a He-Ne laser was passed through a vicinity of a leaf of the plants, which were put in culture dishes filled with acid solutions. Deflection signals of the probe beam were monitored and compared for acid solutions with different pH values. The results of Egria showed that the deflection signals changed dramatically when pH values of acid solutions were 2.0 and 3.0, while little at pH of 4.0 and 5.0. For Cerastium when pH were below 3.0, deflection signals changed greatly with time at the begining. After a certain period of time, deflection signals changed little with time. When pH value was above 4.0, deflection signals of Cerastium were still changing with time even after 20 hours. The results suggested that the damage threshold of pH was between 3.0 and 4.0 for both the land and aquatic plants.

The invasive Egeria densa macrophyte and its potential as a new renewable energy source: A study of degradation kinetics and thermodynamic parameters.

The increase in global demand, along with environmental concerns, has led to the need for new sources that can supply the energy needed for socioeconomic development while reducing pollutant emissions. Aquatic biomasses, especially those of invasive aquatic macrophytes, can be potential energy sources, and this study evaluated the thermal degradation of the invasive Egeria densa macrophytes (EDM) in an inert environment at four heating rates to evaluate its potential as a low-cost biomass and bioenergy source. Pyrolysis experiments were performed using a thermogravimetric analyzer. The thermal profile of invasive EDM has three main events (multiple stages). Stages (i) and (ii) occur at a temperature range of 125-395 °C and represent the decomposition of carbohydrates such as hemicellulose and cellulose. Stage (iii) occurs between 395 and 500 °C and mainly relates to the decomposition of lignin. Thermal data have been used to analyze kinetic parameters through isoconversional methods, and the activation energy (Ea) value of EDM showed variation at different conversion points. The highest Ea values were observed for conversion rates of 0.3-0.6 due to the increased energy required to break down the lignocellulosic chains during decomposition. The small difference between the enthalpy change and Ea values for the different isoconversional methods can be due to a small potential energy barrier, which reflects the feasibility that the reaction can occur under the expected conditions. Gibbs free energy (137-145 kJ mol-1) and high heating value (13.40 MJ/kg) revealed a significant bioenergy potential for EDM biomass.

Organellar Glue: A Molecular Tool to Artificially Control Chloroplast-Chloroplast Interactions.

Organelles can physically interact to facilitate various cellular processes such as metabolite exchange. Artificially regulating these interactions represents a promising approach for synthetic biology. Here, we artificially controlled chloroplast-chloroplast interactions in living plant cells with our organelle glue (ORGL) technique, which is based on reconstitution of a split fluorescent protein. We simultaneously targeted N-terminal and C-terminal fragments of a fluorescent protein to the chloroplast outer envelope membrane or cytosol, respectively, which induced chloroplast-chloroplast interactions. The cytosolic C-terminal fragment likely functions as a bridge between two N-terminal fragments, thereby bringing the chloroplasts in close proximity to interact. We modulated the frequency of chloroplast-chloroplast interactions by altering the ratio of N- and C-terminal fragments. We conclude that the ORGL technique can successfully control chloroplast-chloroplast interactions in plants, providing a proof of concept for the artificial regulation of organelle interactions in living cells.

Hydrogen Peroxide Variation Patterns as Abiotic Stress Responses of Egeria densa.

In vegetation management, understanding the condition of submerged plants is usually based on long-term growth monitoring. Reactive oxygen species (ROS) accumulate in organelles under environmental stress and are highly likely to be indicators of a plant's condition. However, this depends on the period of exposure to environmental stress, as environmental conditions are always changing in nature. Hydrogen peroxide (H2O2) is the most common ROS in organelles. The responses of submerged macrophytes, Egeria densa, to high light and iron (Fe) stressors were investigated by both laboratory experiments and natural river observation. Plants were incubated with combinations of 30-200 µmol m-2 s-1 of photosynthetically active radiation (PAR) intensity and 0-10 mg L-1 Fe concentration in the media. We have measured H2O2, photosynthetic pigment concentrations, chlorophyll a (Chl-a), chlorophyll b (Chl-b), carotenoid (CAR), Indole-3-acetic acid (IAA) concentrations of leaf tissues, the antioxidant activity of catalase (CAT), ascorbic peroxidase (APX), peroxidase (POD), the maximal quantum yield of PSII (Fv Fm -1), and the shoot growth rate (SGR). The H2O2 concentration gradually increased with Fe concentration in the media, except at very low concentrations and at an increased PAR intensity. However, with extremely high PAR or Fe concentrations, first the chlorophyll contents and then the H2O2 concentration prominently declined, followed by SGR, the maximal quantum yield of PSII (Fv Fm -1), and antioxidant activities. With an increasing Fe concentration in the substrate, the CAT and APX antioxidant levels decreased, which led to an increase in H2O2 accumulation in the plant tissues. Moreover, increased POD activity was proportionate to H2O2 accumulation, suggesting the low-Fe independent nature of POD. Diurnally, H2O2 concentration varies following the PAR variation. However, the CAT and APX antioxidant activities were delayed, which increased the H2O2 concentration level in the afternoon compared with the level in morning for the same PAR intensities. Similar trends were also obtained for the natural river samples where relatively low light intensity was preferable for growth. Together with our previous findings on macrophyte stress responses, these results indicate that H2O2 concentration is a good indicator of environmental stressors and could be used instead of long-term growth monitoring in macrophyte management.

A green light-excitable FRET system for monitoring intracellular calcium levels in plant cells.

CFP/YFP-paired FRET is routinely used to estimate intracellular Ca2+ concentrations in vivo. This system, however, is excited with blue light, which is likely to invoke unexpected responses in plant cells. This report describes a new green light-excitable FRET system with an mKO2/mCherry pair. Plant cells expressing this newly constructed FRET system demonstrated its ability to monitor changes in cytosolic free calcium concentration. The new system is likely to find applications in studies of plant cells where undesirable blue light responses must be avoided.

Hydrothermal Carbonization and Pellet Production from Egeria densa and Lemna minor.

Biofuels are seen as a potential option for mitigating the effects of fossil fuel use. On the other hand, nutrient pollution is accelerating eutrophication rates in rivers, lakes, and coastal waters. Harvesting aquatic plants to produce biofuels could mitigate this problem, though it is important to attack the problem at source, mainly as regards the contribution of nutrients. For the first time, solid biofuels were obtained in the forms of carbon and pellets from the aquatic plants Egeria densa, which is classed as an invasive plant under the Spanish Catalogue of Exotic Invasive Species, and Lemna minor, both of which can be found in the Umia River in north-west Spain. The essential oils and macro- and microelements present in both these plants were also extracted and analyzed. The higher heating values (HHVs) of the carbon products obtained ranged from 14.28 to 17.25 MJ/kg. The ash content ranged from 22.69% to 49.57%. The maximum yield obtained for biochar for Egeria densa at 200 °C was 66.89%. Temperature significantly affects solid hydrochar yield. The HHVs of the pellets obtained ranged from 11.38 to 13.49 MJ/kg. The use of these species to obtain biofuels through hydrothermal carbonization (HTC) and pellets is a novel and effective approach that will facilitate the removal of nutrients that cause eutrophication in the Umia River. The elements extracted show that harvesting these plants will help to remove excessive nutrients from the ecosystem.

Particle bombardment and subcellular protein localization analysis in the aquatic plant Egeria densa.

Particle bombardment is a powerful and relatively easy method for transient expression of genes of interest in plant cells, especially those that are recalcitrant to other transformation methods. This method has facilitated numerous analyses of subcellular localization of fluorescent fusion protein constructs. Particle bombardment delivers genes to the first layer of plant tissue. In leaves of higher plants, epidermal cells are the first cell layer. Many studies have used the epidermal cell layer of onion bulb (Allium cepa) as the experimental tissue, because these cells are relatively large. However, onion epidermal cells lack developed plastids (i.e., chloroplasts), thereby precluding subcellular localization analysis of chloroplastic proteins. In this study, we developed a protocol for particle bombardment of the aquatic plant Egeria densa, and showed that it is a useful system for subcellular localization analysis of higher plant proteins. E. densa leaflets contain only two cell layers, and cells in the adaxial layer are sufficiently large for observation. The cells in both layers contain well-developed chloroplasts. We fused fluorescent proteins to conventional plant localization signals for the nucleus, cytosol, mitochondria, peroxisome, and chloroplast, and used particle bombardment to transiently express these fusion constructs in E. densa leaves. The plant subcellular localization signals functioned normally and displayed the expected distributions in transiently transformed E. densa cells, and even chloroplastic structures could be clearly visualized.

Biomethane recovery from Egeria densa in a microbial electrolysis cell-assisted anaerobic system: Performance and stability assessment.

Renewable energy recovery from submerged aquatic plants such as Egeria densa (E. densa) via continuous anaerobic digestion (AD) represents a bottleneck because of process instability. Here, a single-chamber membrane-free microbial electrolysis cell (MEC) equipped with a pair of Ti/RuO2 mesh electrodes (i.e. the combined MEC-AD system) was implemented at different applied voltages (0-1.0 V) to evaluate the potential effects of bioelectrochemical stimulation on methane production and process stability of E. densa fermentation. The application of MEC effectively stabilized E. densa fermentation and upgraded overall process performance, especially solid matters removal. E. densa AD process was operated steadily throughout bioelectrochemical process without any signs of imbalance. The solubilization-removal of solid matters and methane conversion efficiency gradually increased with increasing applied voltage, with an average methane yield of approximately 248.2 ± 21.0 mL L(-1) d(-1) at 1.0 V. Whereas, the stability of the process became worse immediately once the external power was removed, with weaken solid matters removal along with methane output, evidencing the favorable and indispensable role in maintaining process stability. The stabilizing effect was further quantitatively demonstrated by statistical analysis using standard deviation (SD), coefficient of variance (CV) and box-plots. The syntrophic and win-win interactions between fermenting bacteria and electroactive bacteria might have contributed to the improved process stability and bioenergy recovery.

Water level fluctuations in a tropical reservoir: the impact of sediment drying, aquatic macrophyte dieback, and oxygen availability on phosphorus mobilization.

Reservoirs in semi-arid areas are subject to water level fluctuations (WLF) that alter biogeochemical processes in the sediment. We hypothesized that wet-dry cycles may cause internal eutrophication in such systems when they affect densely vegetated shallow areas. To assess the impact of WLF on phosphorus (P) mobilization and benthic P cycling of iron-rich sediments, we tested the effects of (i) sediment drying and rewetting, (ii) the impact of organic matter availability in the form of dried Brazilian Waterweed (Egeria densa), and (iii) alternating redox conditions in the surface water. In principle, drying led to increased P release after rewetting both in plant-free and in plant-amended sediments. Highest P mobilization was recorded in plant amendments under oxygen-free conditions. After re-establishment of aerobic conditions, P concentrations in surface water decreased substantially owing to P retention by sediments. In desiccated and re-inundated sediments, P retention decreased by up to 30% compared to constantly inundated sediments. We showed that WLF may trigger biochemical interactions conducive to anaerobic P release. Thereby, E. densa showed high P release and even P uptake that was redox-controlled and superimposed sedimentary P cycling. Macrophytes play an important role in the uptake of P from the water but may be also a significant source of P in wet-dry cycles. We estimated a potential for the abrupt release of soluble reactive phosphorus (SRP) by E. densa of 0.09-0.13 g SRP per m(2) after each wet-dry cycle. Released SRP may exceed critical P limits for eutrophication, provoking usage restrictions. Our results have implications for management of reservoirs in semi-arid regions affected by WLF.

Thigmomorphogenetic responses of an aquatic macrophyte to hydrodynamic stress.

The response of aquatic plants to abiotic factors is a crucial study topic, because the diversity of aquatic vegetation is strongly related to specific adaptations to a variety of environments. This biodiversity ensures resilience of aquatic communities to new and changing ecological conditions. In running water, hydrodynamic disturbance is one of the key factors in this context. While plant adaptations to resource stress (nutrients, light…) are well documented, adaptations to mechanical stress, particularly flow, are largely unknown. The submerged species Egeria densa was used in an experiment to detect whether the presence or absence of hydrodynamic stress causes plant thigmomorphogenetic responses (i) in terms of plant biogenic silica (BSi), cellulose and lignin concentrations, and (ii) in terms of plant strength. Plant silica concentrations, as well as lignin concentrations were significantly higher in presence of hydrodynamic stress. These physiological changes are accompanied by some significant changes in stem biomechanical traits: stem resistance to tensile forces (breaking force and breaking strength) and stiffness were higher for plants exposed to hydrodynamic stress. We conclude that the response of this aquatic plant species to mechanical stress is likely the explaining factor for a higher capacity to tolerate stress through the production of mechanically hardened shoots.

Assessment of metal sorption mechanisms by aquatic macrophytes using PIXE analysis.

In this work, a study of the metal sorption mechanism by dead biomass has been performed. All batch metal biosorption experiments were performed using the aquatic macrophyte Egeria densa as biosorbent. Divalent cadmium and zinc solutions were used to assess the sorption mechanisms involved. Using a suitable equilibrium time of 2h and a mixture of 300 mg biosorbent and 50 mL metal solution at pH 5, monocomponent sorption experiments were performed. In order to determine the residual amounts of metals in the aqueous solutions and the concentrations of removed metals in the dry biomass, Particle Induced X-ray Emission (PIXE) measurements in thin and thick target samples were carried out. Based on the strong experimental evidence from the mass balance among the major elements participating in the sorption processes, an ion exchange process was identified as the mechanism responsible for metal removal by the dry biomass.

The effect of habitat and sediment type on the occurrence of non-native and native species of aquatic macrophyte in subtropical regions / Efeito do habitat e do tipo de sedimento na ocorrência de uma espécie não-nativa e uma espécie nativa de macrófita aquática na região subtropical

Non-native species of aquatic plants may become invasive and affect native communities, reducing the diversity of plants and other organisms. In general, the successful colonization of new habitats by macrophytes depends first on their dispersion ability and second on the existence of favorable abiotic conditions. In this investigation, we used a transplant experiment to test the effects of habitat water (main river channel versus lake) and habitat sediment (river sediment versus lake sediment) on the growth of two species, the non-native Hydrilla verticillata and the native macrophyte Egeria najas. We tested the hypothesis that the non-native species is more successful when it grows in the river channel with river sediment as substrate, whereas the native E. najas is more successful when it grows in the lake with lake sediment as substrate. Fragments of both species were planted in river and lake sediment and transported to the main river channel and a lake for the growing period. The field experiment results demonstrated that H. verticillata did not grow in either river or lake sediment when planted in the lake. However, this species developed higher root biomass than E. najas in the main river channel, which explains its predominance in this type of habitat. The results support the view that habitat characteristics are determinants of the successful or unsuccessful growth of H. verticillata in our study sites. Finally, H. verticillata invasiveness may improve after certain lag times in response to alterations in habitat, as observed for several other non-native species. Thus, future invasions of floodplain lakes by this species cannot be discarded.

Espécies não-nativas de plantas aquáticas podem se tornar invasoras e afetar as comunidades nativas, reduzindo a diversidade de plantas e de outros organismos. Em geral, a colonização por macrófitas em novos habitats depende em primeiro lugar de sua capacidade de dispersão e à existência de condições abióticas favoráveis. Nesta investigação foi utilizado um experimento de transplante para testar os efeitos da água do habitat (calha principal do rio versus lago) e sedimentos do habitat (sedimento do rio versus sedimento do lago) sobre o crescimento de duas espécies de macrófitas aquáticas a não-nativa Hydrilla verticillata e nativa Egeria najas. Foi testada a hipótese de que as espécie não-nativa é mais bem sucedida quando cresce no canal do rio com sedimento do rio como substrato, enquanto a nativa E. najas é mais bem sucedida quando cresce no lago com sedimento do lago como substrato. Fragmentos de ambas as espécies foram plantadas em sedimentos do rio e do lago e transportadas para o Rio e um lago para o cultivo. Resultados em campo mostraram que H. verticillata não cresceu no lago, em ambos os sedimentos (rio e lago). No entanto, esta espécie desenvolveu maior biomassa da raiz no rio, comparada a E. najas, o que explica sua predominância neste tipo de habitat. Os resultados apóiam a visão de que as características do habitat são determinantes para o sucesso ou insucesso de H. verticillata nos locais em que foram estudados. Finalmente, a invasão H. verticillata pode melhorar após um determinado intervalo de tempo em resposta a alterações no habitat, como observado para várias outras espécies não-nativas e, portanto, a futura invasão de lagos de várzea por esta espécie não pode ser descartada.

Effects of a native and a non-native macrophyte species of Hydrocharitaceae on Chironomidae and Oligochaeta assemblages structure / Efeitos de uma espécie de macrófita nativa e uma invasora de Hydrocharitaceae sobre a estrutura das assembleias de Chironomidae e Oligochaeta

This study investigated the structure of the Oligochaeta and Chironomidae assemblages associated with monospecific stands of two submerged macrophyte species: Egeria najas and Hydrilla verticillata. Samplings were carried out in Leopoldo Backwater and Paraná river, in August 2008. To assess the structure of Oligochaeta and Chironomidae assemblage in each macrophyte we calculated: species density, richness, diversity, and evenness. A detrended correspondence analysis (DCA) was used to summarize Oligochaeta and Chironomidae assemblages composition. The highest values of species density and richness for the two groups were recorded in H. verticillata. Although there were no significant differences in density, richness and Shannon diversity, the assemblage composition of these groups was significantly different between plant species. These results suggest that despite being a recent colonizer in the upper Paraná river habitats, the non-native species H. verticillata seems to provide favorable conditions for the establishment of native assemblages of Chironomidae and Oligochaeta. Moreover, differences in the species composition of Oligochaeta and Chironomidae arose from peculiar characteristics of each plant, as attached microorganisms and organic matter, so that other factors, rather than plant architecture can also influence the assemblage of these groups.

Este estudo objetivou investigar a estrutura da assembleia de Oligochaeta e Chironomidae em associação com bancos puros de duas espécies de macrófitas submersas: Hydrilla verticillata e Egeria najas. As coletas foram realizadas no ressaco do Leopoldo e no rio Paraná, em agosto de 2008. Para avaliar a estrutura da assembleia de Oligochaeta e Chironomidae em cada macrófita foram calculados: densidade, riqueza, diversidade de Shannon e equitabilidade. Uma análise de correspondência destendenciada (DCA) foi usada para sumarizar a composição da assembleia de Oligochaeta e Chironomidae. Os maiores valores de densidade e riqueza para os dois grupos foram registrados na H. verticillata. Embora não houvesse nenhuma diferença significativa na densidade, riqueza e diversidade de Shannon, a composição da assembleia desses grupos foi significativamente diferente entre as macrófitas. Esses resultados sugerem que apesar de ser uma colonizadora recente dos habitats do alto rio Paraná, H. verticillata parece prover condições favoráveis para o estabelecimento das assembleias de Oligochaeta e Chironomidae. Além disso, diferenças na composição de espécies desses grupos ocorreram devido às características peculiares de cada planta, como micro-organismos e matéria orgânica aderidos, de forma que outros fatores, em vez de arquitetura da planta, podem também influenciar a assembleia desses grupos.