Phenotypic plasticity as a clue for invasion success of the submerged aquatic plant Elodea nuttallii

• Two closely related alien submerged aquatic plants were introduced into Europe. The new invader (Elodea nuttallii) gradually displaced E. canadensis even at sites where the latter was well established. The aim of the study was to evaluate the combined effects of environmental factors on several phenotypic characteristics of the two Elodea species, and to relate these phenotypic characteristics to the invasion success of E. nuttallii over E. canadensis.
• In a factorial design, Elodea plants were grown in aquaria containing five different nitrogen concentrations and incubated at five different light intensities. We used six functional traits (apical shoot RGR), total shoot RGR, relative elongation, root length, lateral spread, branching degree) to measure the environmental response of the species. We calculated plasticity indices to express the phenotypic differences between species.
• Light and nitrogen jointly triggered the development of phenotypic characteristics that make E. nuttallii a more successful invader in eutrophic waters than E. canadensis. The stronger invader showed a wider range of phenotypic plasticity. The apical elongation was the main difference between the two species, with E. nuttallii being more than two times longer than E. canadensis. E. canadensis formed dense side shoots even under high shade and low nitrogen levels, whereas E. nuttallii required higher light and nitrogen levels.
• We found that under more eutrophic conditions, E. nuttallii reach the water surface sooner than E. canadensis and through intensive branching outcompetes all other plants including E. canadensis. Our findings support the theory that more successful invaders have wider phenotypic plasticity.

     

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

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Strong growth limitation of a floating plant (Lemna gibba) by the submerged macrophyte (Elodea nuttallii) under laboratory conditions

1. The asymmetric competition for light and nutrients between floating and submerged aquatic plants is thought to be key in explaining why dominance by either of these groups can be stable and difficult to change. 2. Although the shading effect of floating plants on submerged plants has been well documented, the impact of submerged plants on floating plants has been poorly explored hitherto. 3. Here, we used laboratory experiments to examine how submerged plant (Elodea nuttallii) alter nutrient conditions in the water column and how this affects the growth of floating plants (Lemna gibba). 4. We demonstrate that, at higher nutrient concentrations, Lemna is increasingly likely to outcompete Elodea. 5. Under low nutrient concentrations (0.1–2 mg N L^?1) Elodea can strongly reduce the growth of Lemna. Growth of floating plants virtually stopped in some of the experiments with Elodea. 6. Extremely reduced tissue N, Mn, chlorophyll and elongated roots indicated that the growth inhibition of Lemna by Elodea was predominantly caused by the latter’s impact on the nutrient conditions for floating plants. 7. These results strengthen the hypothesis that submerged plants can prevent colonization of a lake by floating plants.     

Studies of Elodea nuttallii grown under photorespiratory conditions. II. Evidence for bicarbonate active transport

Abstract. Elodea nuttallii was grown under greenhouse conditions in domestic wastewater in an aquatic treatment system under conditions conducive to photorespiration. Initial research on the photosynthetic characteristics of E. nuttallii suggest that the submergent macrophyte possessed a carbon concentrating mechanism. Isotopic disequilibria H¹⁴CO₃-uptake studies (5-80s) were used to assess the bicarbonate active-transport capabilities in E. nuttallii leaves. Using a range of substrate concentrations (50-50200mmol m^?3), the accumulation of label (mmol g^?1 Chl) over time due to transport was found initially to exceed accumulation due to fixation until steady state rates were observed. Internal steady state pools of dissolved inorganic carbon (DIC) ranged from 40 to 80 mol m^?3. The concentration factor (CF: the ratio of internal cyroplasmic (DIC] to external medium [DIC]) decreased from 800 to 114 as external bicarbonate concentrations were increased. Inhibition of transport by uncouplers (2,4-dinitrophenol (DNP), carbonyl cyanide-m-chlorophenylhydrazone (CCCP)); ATPase inhibitors (dicylcohexocarbodiamide (DCCD), phloridzin, arsenate); electron transport inhibitors (DCMU, Antimycin A), and carbonic anhydrase inhibitors (ethoxyzolamide, acetazolamide) suggest that bicarbonate transport required (1) a proton motive force, (2) a functional ATPase, (3) a chloroplast carbon sink, and possibly (4) a CA-like moiety associated with the transport protein. While plasmalemmasomes were not observed, the plasmalemma was vesiculated and acid and alkaline banding was observed when leaves were incubated under light in the presence of bicarbonate. These data are consistent with the operation of a bicarbonate-cation symport which concentrates substrate against a concentration gradient at the expense of metabolic energy. The presence of an active transport system for bicarbonate ensures that internal carbon concentrations are high when carbon dioxide, is scarce and bicarbonate is the only carbon species available in aquatic treatment systems during photorespiratory conditions. Therefore, E. nuttallii is particularly well suited for use in these systems.     

牧食损害对伊乐藻(Elodea nuttallii)生长的影响

在室外实验条件下,研究了模拟牧食损害(动物牧食所造成的损害)对伊乐藻植株生长的影响。结果表明:3种人工损害方式(去除植株50%叶片,去除植株顶端,以及同时去除植物顶端与50%叶片)对伊乐藻的生长率、主枝与分枝长度的增长、植物的干物质、氮、磷含量等均有不同程度的影响。其中,去叶与去顶去叶损害显著抑制了伊乐藻的生长,相对生长率分别占未受损植株的62.8%与74.4%;去顶与去顶去叶损害使伊乐藻主枝生长几乎停止,却显著促进了植物分枝的生长;去叶损害对植株的生长率、主枝与分枝长度的生长无明显抑制并却显著地降低了分枝的重量。对受损伊乐藻生长的机理进行了分析,探讨了东太湖伊乐藻现存量近年来迅速增加的原因并认为植物残体是伊乐藻种群扩张的重要因素之一。     

伊乐藻对浮游动物群落结构的影响

浮游动物是淡水生态系统的重要组成部分,一方面浮游动物主要以浮游植物作为食物^[1],同时又能摄食细菌^[2、3]、原生动物^[4、5];另一方面浮游动物又是一些鱼类优良的食物^[6、7]。国内外一些研究发现,有大量沉水植物存在的湖区,浮游动物的种类数、数量、生物量和多样性都比存在少量或没有沉水植物的湖区要高^[8-13]。     

伊乐藻(Elodea nuttallii)对高浓度氮磷营养盐的耐受性

通过5个相对恒定的TN、TP浓度梯度下伊乐藻(Elodea nuttallii)的生长实验,探讨了伊乐藻对高浓度氮磷营养盐的耐受性,比较了各营养盐浓度下水体的pH值、DO、浮游藻类叶绿素a和附着藻类叶绿素a以及伊乐藻的株高、湿质量、干质量和叶绿素a含量.结果表明:在实验条件下,伊乐藻能耐受TN=10 mg·L~(-1),TP=0.4 mg·L~(-1)的胁迫,且在该营养盐水平下水体中没有出现大量的浮游藻类;而在TN=50 mg·L~(-1)、TP=2 mg·L~(-1)和TN=100 mg·L~(-1)、TP=4 mg·L~(-1)的高营养盐条件下,伊乐藻的生长受到了明显的抑制,同时水体中的浮游藻类明显增多,而附着藻类则明显减少;在高营养盐水平下,一方面水体中的某些营养盐可能对伊乐藻产生了直接伤害,另一方面水体中浮游藻类的增多,所导致的遮光作用也可能限制了其生长;对水体中营养盐的平均水平低于TN=10 mg·L~(-1),TP=0.4 mg·L~(-1)的太湖而言,沉水植被的消亡可能不是由于氮磷营养盐所产生的直接伤害和胁迫.     

Sediment-related growth limitation of Elodea nuttallii as indicated by a fertilization experiment

1. A fertilization experiment was performed to identify the limiting nutrient for the growth of submerged vegetation in ditches of a peat-grassland system in the Netherlands, in which restoration measures involved ceasing fertilization, exporting nutrients by removal of above-ground plant mass and large-scale introduction of calcium-rich, nutrient-poor artesian water.
2. Growth of Elodea was significantly enhanced by enrichment with nitrogen alone, and by fertilization with nitrogen in combination with phosphorus, and by nitrogen in combination with phosphorus and potassium.
3. Plant tissue nutrient concentrations increased significantly, for nitrogen by enrichment with nitrogen alone, and with nitrogen in combination with phosphorus and potassium; for phosphorus by enrichment with phosphorus alone and with phosphorus in combination with nitrogen and potassium; tissue concentrations of potassium were not enhanced by any treatment.
4. The elemental ratios of treated plants indicated that nitrogen, rather than phosphorus, was limiting in all treatments, except in those involving nitrogen and NK enrichment (when phosphorus was limiting).
5. The efficiency with which plants used nutrients declined with increased supply of nitrogen and phosphorus, but was unchanged when potassium was increased. Efficiencies were similar to those of other aquatic macrophytes.     

Sediment-related growth limitation of Elodea nuttallii as indicated by a fertilization experiment

1. A fertilization experiment was performed to identify the limiting nutrient for the growth of submerged vegetation in ditches of a peat-grassland system in the Netherlands, in which restoration measures involved ceasing fertilization, exporting nutrients by removal of above-ground plant mass and large-scale introduction of calcium-rich, nutrient-poor artesian water.
2. Growth of Elodea was significantly enhanced by enrichment with nitrogen alone, and by fertilization with nitrogen in combination with phosphorus, and by nitrogen in combination with phosphorus and potassium.
3. Plant tissue nutrient concentrations increased significantly, for nitrogen by enrichment with nitrogen alone, and with nitrogen in combination with phosphorus and potassium; for phosphorus by enrichment with phosphorus alone and with phosphorus in combination with nitrogen and potassium; tissue concentrations of potassium were not enhanced by any treatment.
4. The elemental ratios of treated plants indicated that nitrogen, rather than phosphorus, was limiting in all treatments, except in those involving nitrogen and NK enrichment (when phosphorus was limiting).
5. The efficiency with which plants used nutrients declined with increased supply of nitrogen and phosphorus, but was unchanged when potassium was increased. Efficiencies were similar to those of other aquatic macrophytes.     

烯效唑对沉水植物伊乐藻(Elodea nuttallii)生长及抗氧化酶活性的影响

研究了烯效唑对沉水植物伊乐藻生长及抗氧化酶活性的影响。结果表明,烯效唑可以刺激伊乐藻新芽萌发,新生枝条节间距减小,叶片紧密,同时烯效唑对成熟枝条的生长具有明显的抑制作用。低浓度（≤1．0mg／L）、短时间的烯效唑暴露可促进叶绿素a含量的增加,随着暴露时间的延长,处理组叶绿素a含量降低,叶绿素b含量显著增加。烯效唑胁迫下,伊乐藻体内3种抗氧化酶反应灵敏,SOD活性受到显著诱导,CAT活性先升高后降低,POD活性先升高后降低后又升高。说明烯效唑可对植物产生氧化胁迫,诱导抗氧化酶活性升高,当胁迫超过一定强度时,活性氧不能及时清除,对植物体产生氧化损伤。     

Radioecological monitoring of the Yenisei River and citological characterization of a submerged aquatic plant Elodea canadensis

The study was devoted to investigation of the contents of radionuclides and of heavy metals and to evaluate the frequency of chromosomal aberrations in samples of Elodea canadensis, a submerged plant, collected in different parts of the Yenisei River. The samples were collected in the area subjected to radioactive impact of the Mining-and-Chemical Combine (MCC) at Zheleznogorsk and in the control area, upstream of the MCC. The investigations shown that elodea biomass in the area affected by MCC operation contained a long inventory of artificial radionuclides typical for the MCC discharges. The upstream of the MCC, in the control sampling area, the sediments and the elodea biomass contained only one artificial radionuclide--137Cs. Thus, the exposure doses to elodea shoots and roots upstream of the MCC are small (not more than 8 microGy/d) and the main contribution info the dose is made by natural radionuclides. At the MCC discharge site (the village of Atamanovo) and at the downstream of it, the total dose rate increases almost an order of magnitude, reaching its maximal values--72 microGy/d for elodea shoots and 58 microGy/d for its roots. Cytogenetic investigations of elodea roots shown that at the MCC discharge site (the village of Atamanovo) and at downstream of it the occurrence of chromosomal aberrations in ana-telophase and in metaphase cells of elodea was considerably higher than in the control area. It is highly probable that this simultaneous dramatic increase in the total exposure rate and the occurrence of chromosomal aberrations in elodea is associated with the radiation factor. It is suggested that elodea is affected not only by the radiation factor but also by the chemical factor--toxicity of heavy metals.     

Studies of Elodea nuttallii grown under photorespiratory conditions. I. Photosynthetic characteristics

Abstract. The photosynthetic characteristics of Elodea nuttallii grown in wastewater in continuous flow reactors in a greenhouse were investigated. The diurnal changes in dissolved inorganic carbon (DIC), dissolved oxygen (DO) and pH were monitored. Photosynthesis removed both CO₂(aq) and HCO₃^? from the reactors. A stoichiometry of 1.19:1 was observed between HCO₃^? removal during photosynthesis and OH^? production during photosynthesis, consistent with theories regarding direct bicarbonate utilization. In laboratory experiments, the light compensation points (г_PPFD) were similar (31–35μmol m^?2 s^?1) to reported values for other macrophytes; however, the light saturation level was high (1100μmol m^?2 s^?1) and similar to values reported for aerial portions Of heterophyllous macrophytes. The kinetics of photosynthetic oxygen evolution (K_m (CO₂) = 96mmol m^?3; V_max= 133mmol g^?1 Chl h^?1) and the CO₂ compensation point (г= 44cm³ m^?3) suggested an adaptive, low photorespiratory state in response to low carbon concentrations. Photosynthetic V_max values were slightly, but significantly higher (P 0.001) at pH 8.0 compared to pH 4.5. While CO₂ utilization at pH 8 could account for most of the observed phototsynthetic rates, an HCO₃^? component was present, suggesting two separate transport systems for HCO₃^? and CO₂(aq) in E. nuttallii. The activity of RUBISCO (160.3 mmol g^?1 Chl h^?1 was one of the highest reported values for aquatic macrophytes. Compared to RUBISCO, we observed lower activities of the β-carboxylating enzymes phopho enolpyruvate carboyxlase (PEPcase), 24.1 mmol g^?1 Chl h^?1; phosphor enol pyruvate carboxykinase (PEPCKase), 14 mmol g^?1 Chl h^?1. This suggests that the potential light-independent fixation of carbon in E. nuttallii was much less than RUBISCO-dependent fixation. The RUBISCO/PEPcase ratio was 6.6, indicating that E. nuttallii was similar to Myriophyllum sp. in possessing a physiological adaptation to low CO₂ levels which is hypothesized to include carbonic anhydrase (CA) and an active transport system for HCO₃^?. CA levels were surprisingly low in E. nuttallii (14.2 EUmg Chl^?).     

螺类牧食对伊乐藻与苦草种间关系的影响

动物牧食可以调节植物种间的相对竞争能力,从而改变物种在群落中的竞争地位.外来植物伊乐藻生长迅速、具有较强的光竞争能力,土著种苦草根系发达、具有较强的地下资源竞争能力.选择这两种各具竞争特色的沉水植物为模式生物,通过室外受控实验研究了螺类牧食对两种沉水植物种间关系的影响.结果表明:不管有无螺类牧食,伊乐藻的相对生长率为苦草的2～5倍,伊乐藻具有明显的竞争优势.苦草低密度种植时,螺类牧食与种间竞争对其生长没有显著影响;高密度种植时,螺类牧食活动促进了苦草的生长,种间竞争则使苦草的生长率明显降低.无论伊乐藻种植密度如何,螺类牧食均使其生长率明显降低,混栽高密度的苦草也能抑制伊乐藻生长.探讨了螺类牧食对沉水植物的种间竞争关系的作用机理.     

Acetogenins from the aquatic plant Elodea canadensis

13-(2-furyl)-Tridec-12E-en-1-yne and (7S)-hydroxyhexadeca-8E,10Z,13Z-trienoic acid have been isolated from Elodea canadensis in addition to the already known 13-(2-furyl)-tridec-1-yne, hexadec-11Z-enoic, hexadeca-7Z,10Z,13Z-trienoic and (10R)-hydroxyhexadeca-7Z,11E,13Z-trienoic acids.     

Increasing canopy shading reduces growth but not establishment of Elodea nuttallii and Myriophyllum spicatum in stream channels

In aquatic environments around the globe, rooted macrophytes have been replaced by filamentous macroalgae. The consequences of such shifts in vegetative habitat for fauna are poorly understood. Given differences in morphology and life history characteristics of rooted macrophytes and filamentous macroalgae, we hypothesized that these habitat types were not functionally redundant for small-bodied fishes and macroinvertebrates. We examined this hypothesis in spring-fed Florida rivers characterized by decreases in native rooted macrophytes and concomitant increases in filamentous macroalgae. Although faunal densities were generally greater in filamentous macroalgae than in rooted macrophytes, differences in the community assemblage structure suggest that the two types of vegetative habitat do not function interchangeably. Accordingly, continued replacement of rooted macrophytes with filamentous macroalgae is expected to affect the small fish and macroinvertebrate community, as well as higher trophic levels that depend on it.     

Studies of Elodea nuttallii grown under photorespiratory conditions. III. Quantitative cytological characteristics

Abstract. Elodea nuttallii was grown in primary effluent from domestic wastewater under conditions in which CO₂ may be limiting. However, high photosynthetic inorganic carbon uptake rates have been reported for Elodea under these conditions. In order to determine if leaf cell structure showed modifications which would support proposed models of a plasma membrane (PM) bicarbonate transport system and observed high photo-synthetic rates, leaf cell ultrastructure was analysed using quantitative techniques (stereology). A Fold Index (FI) calculated for the PM showed that infolding increased surface area to 2.15 times that of an idealized cell of the same shape and size. Association Indices (Sa) showed a significant association of the mitochondria with the PM. These observations support models for an ATPase-driven HCO₃-cation cotransport system in Elodea cells. High chloroplast thylakoid surface density values (Sv) were similar to C₄:monocots and indicated high light-gathering potential. The granal/stromal (g/s), granal/cristae (g/c), and stromal/cristae (s/c) membrane ratios were similar to those of C₃ plant cells. Thus, Elodea chloroplasts and cells exhibited some structural features similar to both C₃ and C₄ plants. Membrane-bound inclusion bodies, which occupied 1% of the cell volume, were also observed in the leaf cells. Cell walls and nucleoid regions were absent in these bodies and X-ray (EDAX) analysis failed to detect any element (above the resolution limit of atomic no. 12) in substantial quantities. Inclusion bodies were observed in both the cytoplasm and the periplast and remain unidentified. A model is proposed for Elodea using an ATPase proton pump in the plasma membrane which extrudes protons into the periplast space between the cell wall and plasma membrane. This proton gradient is coupled to a bicarbonate symport.     

Effect of Elodea nuttallii Roots on Bacterial Communities and MMHg Proportion in a Hg Polluted Sediment

The objective of this study was to assess the effect of a rooted macrophyte Elodea nuttallii on rhizosphere bacterial communities in Hg contaminated sediments. Specimens of E. nuttallii were exposed to sediments from the Hg contaminated Babeni reservoir (Olt River, Romania) in our microcosm. Plants were allowed to grow for two months until they occupied the entirety of the sediments. Total Hg and MMHg were analysed in sediments where an increased MMHg percentage of the total Hg in pore water of rhizosphere sediments was found. E. nuttallii roots also significantly changed the bacterial community structure in rhizosphere sediments compared to bulk sediments. Deltaproteobacteria dominated the rhizosphere bacterial community where members of Geobacteraceae within the Desulfuromonadales and Desulfobacteraceae were identified. Two bacterial operational taxonomic units (OTUs) which were phylogenetically related to sulfate-reducing bacteria (SRB) became abundant in the rhizosphere. We suggest that these phylotypes could be potentially methylating bacteria and might be responsible for the higher MMHg percentage of the total Hg in rhizosphere sediments. However, SRB were not significantly favoured in rhizosphere sediments as shown by qPCR. Our findings support the hypothesis that rooted macrophytes created a microenvironment favorable for Hg methylation. The presence of E. nuttallii in Hg contaminated sediments should therefore not be overlooked.     

伊乐藻、苦草和菹草对磷急性胁迫的响应

水生植被,特别是沉水植被的衰退和消失是水体富营养化过程中的普遍现象[1,2],其原因是多方面的,但较高的水柱氮、磷浓度显然是重要原因之一.     

Present distribution of the genus Elodea in the Alsatian Upper Rhine floodplain (France) with a special focus on the expansion of Elodea nuttallii St. John during recent decades

Three species of Elodea (Elodea canadensis Michaux, E. nuttallii St John and E. ernstiae St John) have colonized Europe from the American continent. All three arrived in the Alsatian Rhine floodplain (north-eastern France) soon after their arrival in Europe, i.e. in the mid-19th century for E. canadensis, and in the mid-20th century for E. nuttallii and E. ernstiae. The paper investigates the present distribution of Elodea spp. in the floodplain by quantifying the species’ respective occurrences and by describing their habitats. The study further focuses on E. nuttallii which is presently colonizing other parts of Europe. It analyses whether it has continued to expand in the Alsatian Rhine floodplain during recent decades, and it checks whether changes in the abundance of E. nuttallii have had an impact on species richness of water plant communities. E.␣nuttallii has been found to be at present one of the most dominant and most frequent aquatic plant species in the study sector, while E. canadensis and E. ernstiae are less abundant. The species’ distributions differ with regard to water chemistry and water temperature: E. canadensis occurs in oligo-mesotrophic, rather stenothermic habitats, whereas E. nuttallii and E. ernstiae can be encountered in meso- to eutrophic sites with little or no arrival of stenothermic ground water. By comparing successive vegetation relevés from the same sites the study revealed further that the distribution of E. nuttallii has been stable in recent decades, despite local fluctuations in abundance. No relationship could be established between those fluctuations and changes in species richness or type of local plant communities. The sum of the results suggests that the expansion of E. nuttallii in the Alsatian Rhine floodplain had been completed prior to the study period. The species’ present distribution in the study sector as well as its position in local plant communities might therefore be considered a model for what can be expected to happen in areas where E.␣nuttallii has only recently arrived.     

Antioxidative responses of Elodea nuttallii (Planch.) H. St. John to short-term iron exposure

Antioxidative responses of Elodea nuttallii (Planch.) H. St. John to short-term iron exposure were investigated in the study. Results showed that iron accumulation in E. nuttallii was concentration dependent. Growth of E. nuttallii was promoted by low iron concentration (1–10 mg L^?1 [Fe³⁺]), but growth inhibition was observed when iron concentration beyond 10 mg L^?1. The synthesis of protein and pigments increased within 1–10 mg L^?1 [Fe³⁺] range. The activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and glutathione-S-transferase (GST) were up to maximal values at 10 mg L^?1 [Fe³⁺]. High iron concentration inhibited the synthesis of protein and pigments as well as activities of antioxidative enzymes, and accelerated degradation of pigment and production of ROS. Low iron concentration had no significant influences on PSII maximal quantum yield, activity of PSII and relative electron transport rate though PSII. Malondialdehyde (MDA) and proline concentrations were highest at 100 and 1 mg L^?1 [Fe³⁺], respectively.