Potamogeton Perfoliatus Research Articles

A quantitative sampler for collecting invertebrates associated with deep submerged vegetation

Only few of the numerous samplers for collecting invertebrate fauna associated with vegetation permit sampling at depths of more than approximately 0.5 m. This paper describes a sampler allowing collection of epifauna from submerged plants at a depth of up to approximately 2 m, growing in varied densities. The sampler is composed of two panels made of duralumin, connected on one side by means of piano-hinges. One of the panels has an opening covered with mesh, and the other is equipped with a cone-shaped net and detachable sample concentrator at its end. The sampler is coupled with a manipulator with a several meter extension for lowering the sampler under water, as well as for its opening, and closing. The initial assessment of the sampler efficiency, verified in beds of Potamogeton perfoliatus, provided similar results as two other, older and commonly used samplers. In comparison with the older devices, the sampler has the advantage of permitting collecting samples from greater depths. It also enables studying both the vertical and horizontal distribution of invertebrates within a plant patch.

Algal mats reduce eelgrass (Zostera marina L.) growth in mixed and monospecific meadows

Harmful algal blooms are considered to be one of the biggest threats to benthic vegetation. The amount of annual algal mats has increased due to eutrophication but their effects on perennial vegetation have rarely been tested in field experiments. In regions where eelgrass (Zostera marina) grows in mixed meadows, plant species richness may ameliorate algal-induced stress through facilitative mechanisms and improve eelgrass growth and survival. To test this, we conducted a 3mo. field experiment at 3.5m depth in the Baltic Sea, where we applied filamentous brown algae (300g ww) to eelgrass monocultures and polycultures (Z. marina, Ruppia cirrhosa, Stuckenia pectinata and Potamogeton perfoliatus). The algal stress period lasted for 13d and plots were sampled after a 5wk recovery period. In both algal-stressed mono- and polycultures, the presence of algal mats significantly reduced eelgrass shoot and root biomass production and affected the leaf growth negatively. Plant richness did not have strong effects on eelgrass growth and eelgrass in both algal-stressed mono- and polycultures showed significantly reduced productivity. Our results clearly demonstrate that loose-lying algal mats pose a serious threat to seagrass meadows and that plant diversity cannot alone ameliorate negative effects by macroalgal mats.

Epiphyton alters the quantity and quality of radiation captured by leaves in submerged macrophytes

This study investigates the effects of the epiphyton and the leaf morphological and biochemical properties on the quality and quantity of radiation reflected from the adaxial leaf surface and radiation transmitted through the leaf tissue. The radiation in the range from 290nm to 800nm was analysed for submerged leaves of Potamogeton perfoliatus, Potamogeton lucens and Sagittaria sagittifolia. In all of these plant species, the epiphytic algal community was dominated by the diatom Cocconeis placentula. The presence of the epiphyton had more pronounced effect on the amount of transmitted light compared to the amount of reflected light. Most of the variability of the reflectance spectra was explained by the epiphyton dry mass at the adaxial surface (15%). Redundancy analysis to explain the variability of the transmittance spectra showed that the epiphyton layer at the abaxial surface of the leaves has a more important role than that at the adaxial surface, with 18% and 3% of the spectra variability explained, respectively. An additional 21% of the transmittance spectra variability was explained by the leaf carotenoid content. Removal of the epiphyton from the adaxial leaf surface resulted in a significant increase in the leaf reflectance along the spectra, with pronounced differences in the UV, violet and blue ranges. The transmittance spectra measured after removal of the epiphyton also showed a marked increase in the UV, violet and blue ranges. This demonstrates the important role of the epiphyton dominated by diatoms for the prevention of potential harmful effects of short-wave radiation.

New generic and species records for the flora of Saudi Arabia

Recent field works in the central and southern regions of Saudi Arabia including agricultural centers have managed to collect four vascular plants new to terrestrial and wetland flora of the country. These new additions include one new genus Malvastrum A. Gray (M. coromandelianum) subsp. capitato-spicatum (O. Kuntze) S.R. Hill, Potamogeton perfoliatus L. (Potamogetonaceae), Euphorbia tirucalli L. (Euphorbiaceae) and Sesuvium portulacastrum (L.) L. (Aizoaceae). Detailed morphological description, distribution and habitat of each of these species are provided along with illustrations and photographs. The report of new additions to the flora of Saudi Arabia indicated that the country needs thorough botanical explorations.

Spatiotemporal variability in the eelgrass Zostera marina L. in the north-eastern Baltic Sea: canopy structure and associated macrophyte and invertebrate communities

Seagrasses are marine angiosperms fulfilling important ecological functions in coastal ecosystems worldwide. Out of the 66 known seagrass species only two inhabit the Baltic Sea and only one, Zostera marina L., is found in its NE part. In the coastal waters of Estonia, where eelgrass grows at its salinity tolerance limit, only scarce information exists on the Z. marina community and there are no data on eelgrass growth. In the current study the community characteristics and growth of eelgrass were studied at four sites: Ahelaid, Saarnaki, and Soru in the West-Estonian Archipelago Sea and Prangli in the Gulf of Finland. Fieldwork was carried out from May to September in 2005. The results showed that eelgrass grew between 1.8 and 6 m with main distribution at 2-4 m. The eelgrass bed had a considerably higher content of sediment organic matter compared to the adjacent unvegetated areas, but this difference was statistically significant only in areas where the movement of soft sediments is higher. The results also showed that altogether 19 macrophytobenthic and 23 invertebrate taxa inhabited the eelgrass stand. The prevailing vascular plants were Stuckenia pectinata and Potamogeton perfoliatus. Besides attached macrophytes, drifting algae were recorded within the eelgrass communities throughout the study period. Most common invertebrate species inhabiting eelgrass stands were Peringia ulvae, Cerastoderma glaucum, Mytilus trossulus, Macoma balthica, Mya arenaria, Theodoxus fluviatilis, and Idotea chelipes. Irrespective of the studied basin, the increasing eelgrass density supported an elevated diversity and abundance of benthic invertebrates. The eelgrass shoot biomass showed a constant increase from May to September. The overall growth pattern was similar for all studied areas but varied among depth strata. The average shoot density of eelgrass was 50-1300 shoot per m 2 , average biomass ranged from (0.75) 7.8 to 37.31 g dw m -2 in spring and from 18.42 to 68.59 g dw m -2 in autumn.

Plants accumulating heavy metals in the Danube River wetlands

BackgroundWe present herein our results regarding the accumulation of four heavy metals (copper, cadmium, lead, and zinc) in four aquatic species plants (Ceratophyllum demersum, Potamogeton pectinatus, Potamogeton lucens, Potamogeton perfoliatus) collected from the Danube River, South-Western part of Romania and their possible use as indicators of aquatic ecosystems pollution with heavy metals.MethodsElements concentration from the vegetal material was determined through Inductively Coupled Plasma – Mass Spectrometry.ResultsThe species were chosen based on their previous use as bioindicators in aquatic ecosystems and due to the fact they are one of the most frequent aquatic plant species of the Danube River ecosystems within the Iron Gates Natural Park. Highest amounts are recorded for Ceratophyllum demersum (3.52 μg/g for Cd; 22.71 μg/g for Cu; 20.06 μg/g for Pb; 104.23 μg/g for Zn). Among the Potamogeton species, the highest amounts of heavy metals are recorded in Potamogeton perfoliatus (1.88 μg/g for Cd; 13.14 μg/g for Cu; 13.32 μg/g for Pb; 57.96 μg/g for Zn). The sequence for the bioconcentration factors (BCFs) calculated in order to describe the accumulation of the four metals is Cd >> Zn > Pb > Cu. Increase of the zinc concentration determines an increase of the cadmium concentration (Spearman rho=0.40, p=0.02).ConclusionsDespite the low ambiental levels of heavy metals, the four aquatic plants have the ability to accumulate significant amounts, which make them useful as biological indicators. BCF value for Ceratophyllum demersum indicated this species as a cadmium hyperaccumulator.

Colonisation by fragments in six common aquatic macrophyte species

Vegetative reproduction is the most common form of propagation in aquatic macrophytes. Fragmentation and consecutive re-rooting of the fragments is one way in which new macrophyte colonies may establish. The success and frequency of this strategy depends on the species and the environment. This study tested how well six species are capable of colonising this way. Tested species are five of the most abundant species of Lake Balaton, where macrophyte recolonisation is still to take place after improving water quality and one potentially invasive species. Fragments of standardized length were examined for survival, rooting rates and length growth during five to six week experiments under laboratory conditions. Effects of species, shoot part (apical or mid-stem part) and seasonality on rooting probability were analysed with logistic regression. Effects on life-cycle were also examined, in terms of continuation of growth and of flowering or seed-set. Species differed significantly in rooting rates and growth, but not in survival rates. Egeria densa, Myriophyllum spicatum and Potamogeton perfoliatus showed the best colonisation properties (survival rates: 95 %, 84 % and 84 %; rooting rates: 88 %, 45 % and 65 %, respectively), while Potamogeton pectinatus colonised less successfully (survival rate: 91 %, rooting rate: 38 %). The annual Najas marina was the only species which frequently reached flowering (61 %), while fragmenting further, without much rooting (rooting rate: 5 %). The non-rooting Ceratophyllum demersum was least impacted by fragmentation and continued growth best, with survival rates of 100 %. Shoot part had a significant influence on rooting rate and length growth. Apical fragments had higher rooting rates and greater length growth than stem fragments, probably due to the action of their meristematic tissue. Differences in the three repetitions of the experiment may be attributable to seasonal changes in colonisation features. It is concluded that recolonisation by fragments might be an effective way for macrophyte populations to recover in Lake Balaton.

Influence of neighboring plants on shading stress resistance and recovery of eelgrass, Zostera marina L.

Stressful environments may enhance the occurrence of facilitative interspecific interactions between plants. In several regions, Zostera marina occurs in mixed assemblages. However, the potential effects of plant diversity on stress responses and stability properties of Z. marina are poorly understood. We investigated the resistance and recovery of Z. marina subjected to shading (1 mo) in a field experiment lasting 2.5 mo. We shaded Z. marina planted in mono- and polycultures (Potamogeton perfoliatus, P. pectinatus, P. filiformis) in a factorial design (Shading×Richness) at 2 m depth. We estimated the resistance and recovery of Z. marina by measuring four response variables. Polyculture Z. marina lost proportionally less biomass than monocultures, thus having a greater resistance to shading. In contrast, after a 1 mo recovery period, monocultures exhibited higher biomass gain, and a faster recovery than polycultures. Our results suggest that plant species richness enhances the resistance of Z. marina through facilitative mechanisms, while the faster recovery in monocultures is possibly due to interspecific competition. Our results highlight the need of a much better understanding of the effects of interspecific interactions on ecosystem processes in mixed seagrass meadows, and the preservation of diverse plant assemblages to maintain ecosystem functioning.

The effect of periphyton on the light environment and production of Potamogeton perfoliatus L. in the mesotrophic basin of Lake Balaton

Light within the littoral zone affects the productivity and interaction between periphyton and its macrophyte substrate. The effect of periphyton on macrophyte photosynthesis, seasonal variation and vertical distribution of periphyton on artificial substrates (plastic strips), and the effect of periphyton on the light environment was studied in Lake Balaton. Data showed that an average of 4.1 ± 0.4 mg (dry weight) cm−2 of periphyton had accumulated on the plastic strips after 8.8 ± 0.4 days. This biomass corresponded to 294 ± 30 μg m−2 chl-a of epiphytic algae and blocked 92.3 ± 0.8 % of the depth specific radiation. Seasonal variation and specific vertical distribution of periphyton were observed. The most active time of periphyton accumulation corresponded to spring up until mid-June. Later in the year, the amount of periphyton significantly decreased. The optimal conditions for periphyton accumulation were at 30–40 cm depth. Most of the light reaching the adaxial leaf surface was attenuated by periphyton, decreasing the production of Potamogeton perfoliatus by 60–80 %. This increased the importance of backscattered light that corresponded to 10–15 % of the macrophyte production. A smaller part of the periphyton consisted of precipitated inorganic material, while epiphytic algae, making up the majority of the periphyton, were connected to both benthic (dominantly benthic penales) and pelagic (very close seasonal dynamics of pelagic and epiphytic biomass) algae. Periphyton affects macrophyte production especially in spring and in the upper water layers even in a mesotrophic water body. This increases the importance of the light absorbed through the abaxial side of the leaf and confirm the role of periphyton in transition from clear to turbid water states.

The sinks of dissolved inorganic nitrogen in surface water of wetland mesocosms

The transport of dissolved inorganic nitrogen in wetlands was investigated in the Yeyahu National Preserve of Beijing, China, from July to December 2011. Stable isotope of nitrogen (15N) as NH4+ was added to experimental mesocosms vegetated by seven common wetland plants. The 15N abundance in soil and various plant parts were measured at prescribed time intervals during the 49-day experimental period. Rapid 15N enrichments were found in soil and aquatic plants during the first sampling event at day 3 and typically increased linearly during the experimental period. Highest 15N enrichment was found in submerged plants, followed by emergent plants and soil. No differences in δ15N values were found among leaves and stems of all submerged plants (Potamogeton pusillus, Potamogeton perfoliatus, Najas marina, Ceratophyllum demersum), suggesting that these plant structures are equally effective in nitrogen assimilation. The roots of P. perfoliatus displayed the lowest enrichment compared to the stems and leaves. Such results indicate that submerged plant roots may have a relatively weak role in nitrogen assimilation. The two emergent plants (Phragmites australis and Typha orientalis) showed no differences in δ15N values among all plant parts, suggesting rapid translocation of nitrogen from roots to other portions. This experiment demonstrates that wetland soil and plant stems and leaves are major sinks for dissolved nitrogen from the surface water and provides valuable insight into nitrogen retention and transport pathways in various wetland plants.

Impact of habitat environment onPotamogeton perfoliatusL. morphology and its within-plant variability in Lake Balaton

Plastic effect of environmental factors acting on an aquatic submerged plant, Potamogeton perfoliatus L. at the plant-level (nutrient availability) and the leaf-level (light intensity) at different sites in Lake Balaton was studied. Light-dependent morphological traits (foliar morphology and internode length) of P. perfoliatus were measured and analysed across the environmental gradients of the lake. The size of leaves was influenced by both trophic state and light environment: nutrient surplus increased the size of leaves by ∼29%, whereas a more heterogeneous light environment resulted in 15% larger leaves. The light environment influenced shoot morphology (internode length) to a greater extent than nutrient surplus (38% vs. 19%). Contrary to this, within-plant morphological variability was significantly higher (41%) at the nutrient limiting sites as a result of diversification effect of the leaf-level environmental factor, light. Foliar parameters and within-plant variability showed correlation only with the total N content of the sediment. Appearance of P. perfoliatus is shaped by counteracting effects: within-plant differentiation, promoted by leaf-level environmental sensitivity and within-plant homogenization triggered by perception of the surroundings at plant-level. Both light attenuation, stimulating an increase of morphological variability, and nutrient surplus, initiating the stabilization of morphological parameters, could have adaptive advantages. The variability of leaf size leads to diversification of foliar parameters, thus increasing the efficiency of light harvest at low-nutrient sites and making responses to changes in the light environment more dynamic. These results suggest that leaf-level-induced diversification is counteracted by the standardization effect triggered by plant-level environmental factors.

Maternal effects and ecological divergence in aquatic plants: a case study in natural reciprocal hybrids between Potamogeton perfoliatus and P. wrightii

AbstractWhen parental taxa are adapted to different habitats, hybrid genotypes are often highly heterogeneous, such that habitat or ecological factors influence hybrid fate and ecological performance. Trait expression in hybrids is not always intermediate between the parents, but may instead be either parental‐like or extreme (transgressive) depending on genetic control of the phenotypes. Maternal effects arising from interspecific interaction between cytoplasmic and nuclear genomes are widely recognized as playing a role in character expression of natural hybrids. Such interaction often leads to hybrid sterility or inviability. When hybrids are viable, however, cytonuclear interaction may contribute to hybrid persistence through its influence on trait expression. To date, maternal influence on hybrid performance has been examined primarily in experimentally produced hybrids, or in natural hybrids without identification of the cross direction owing to difficulty in obtaining species‐specific molecular markers. In aquatic plants, many hybrids persist by extensive clonal growth and are important components of aquatic communities. Many such hybrids are known in Potamogeton (pondweeds), the largest aquatic genus. Because Potamogeton species are ecologically highly diverse and maternal lineages are readily distinguished using molecular markers, natural hybrids of Potamogeton are well‐suited for studies of maternal effects, especially those affecting vegetative performance. As a case study, we have focused on maternal effects on drought tolerance and depth distribution in the natural hybrid P. × anguillanus derived from the closely related species P. perfoliatus and P. wrightii.

Peculiarities of Epiphyton Algal Communities Formation on Different Macrophyte Species

Abstract Karosienė J., Kasperovičienė J., 2012: Peculiarities of epiphyton algal communities formation on different macrophyte species [Skirtingų makrofitų rūšių epifitono dumblių bendrijų formavimosi ypatumai]. - Bot. Lith., 18(2): 154-163. The epiphyton on different aquatic vegetation represented by emerged macrophytes (Phragmites australis, Equisetum fluviatile, Schoenoplectus lacustris), floating-leaved plants (Nuphar luteum) and submerged macrophytes (Potamogeton perfoliatus, Chara rudis) was studied in two meso- and mesoeutrophic lakes. The morphological characteristics, physiological and synecological peculiarities of plant host had more effect on epiphyton algae abundance and biomass than species richness. The highest densities of algae were associated with helophytes Phragmites australis, Equisetum fluviatile, the lowest was recorded on Schoenoplectus lacustris and laminae of Nuphar luteum. Loosely attached diatoms prevailed on helophytes, adnate species on Nuphar luteum laminae. Cyanobacteria and green algae were more abundant on Nuphar luteum laminae and Potamogeton perfoliatus.

The uptake and distribution of selenium in three aquatic plants grown in Se(IV) solution

The uptake of Se(IV) by Myriophyllum spicatum, Ceratophyllum demersum and Potamogeton perfoliatus, and the effects of Se(IV) on their physiological and biochemical characteristics were studied. Plants were cultivated outdoors under semi-controlled conditions in water solution containing Na selenite (20μgSeL−1 and 10mgSeL−1). The higher concentration of Se lowered the photochemical efficiency of PSII in all species studied, while the lower concentration had no effect on any species. The higher concentration of Se lowered respiratory potential in M. spicatum. The response of M. spicatum and C. demersum to Se(IV) regarding chlorophylls was variable, however in the majority of cases, there was a trend of increasing the amount of chlorophylls, while in P. perfoliatus the amount of chlorophyll a decreased. The concentration of Se in plants cultured in 10mgSe(IV)L−1 ranged from 436 to 839μgSeg−1 DM in M. spicatum, 319 to 988μgSeg−1 DM in C. demersum and 310 to 661μgSeg−1 DM in P. perfoliatus. The amount of soluble Se compounds in enzyme extracts of high Se treatment was 27% in M. spicatum, 41% in C. demersum and 35% in P. perfoliatus. Se compounds were determined using HPLC–ICP-MS. It was observed that the applied Se(IV) was mainly transformed to insoluble Se.

Dynamics of Nutrient Contents (Phosphorus, Nitrogen) in Water, Sediment and Plants After Restoration of Connectivity in Side‐Channels of the River Rhine

AbstractDuring the last century, canalization of the Rhine river led to disconnection of side‐arms, over‐sedimentation of these channels, loss of the fluvial dynamics, and aquatic vegetation change or disappearance. Recent restoration projects aim to reconnect disconnected arms to the main channel. The objective of this study was to assess the nutrient dynamics in restored channels during the vegetation colonization process. In spring, summer, and autumn 2009, the phosphorus and nitrogen contents were measured in water, sediment, and plants, sampled in six channels, two reference sites and four restored ones at different dates. Aquatic vegetation was monitored during the same period. Sites were mesotrophic related to the water nutrient concentrations. However, vegetation communities indicated a eutrophic level, as they were dominated by species like Elodea nuttallii, Myriophyllum spicatum, and Potamogeton perfoliatus. Sites were discriminated by P content and mineral nitrogen in the sediment. We showed an effect of species and season on the plant nutrient content, but there was no relationship between plant nutrient content and nutrients in water and sediment. A negative correlation between mean N plant content and the cover of each species was found. Vegetation characteristics (species richness and cover) and bioavailable phosphorus in the sediment were also correlated. In the restored side‐arms of the river Rhine, phosphorus‐rich sediment seems to be important in the recolonization dynamics, as it was linked to higher species richness, whereas nitrogen played a role in the colonization patterns as a growth limiting factor.

Metal content in higher aquatic plants in a small siberian water reservoir

The dynamics of metal content in higher aquatic plants (macrophytes) in a small Bugach water reservoir in 1998–2006 was studied. A comparative estimation of the metal content in six macrophyte species (Typha latifolia L., Typha angustifolia L., Polygonium amphibium L., Potamogeton perfoliatus L., Potamogeton pectinatus L., Phragmites australis (Cav) Trin. Ex Steud.) showed that their metal concentrations do not generally exceed those known from the literature. Cluster analysis showed that the macrophyte species under study form two ecological groups with respect to the metal content, i.e., submerged plants (hydrophytes) and emergent aquatic plants (heliophytes).

Ocean acidification and the loss of phenolic substances in marine plants.

Rising atmospheric CO2 often triggers the production of plant phenolics, including many that serve as herbivore deterrents, digestion reducers, antimicrobials, or ultraviolet sunscreens. Such responses are predicted by popular models of plant defense, especially resource availability models which link carbon availability to phenolic biosynthesis. CO2 availability is also increasing in the oceans, where anthropogenic emissions cause ocean acidification, decreasing seawater pH and shifting the carbonate system towards further CO2 enrichment. Such conditions tend to increase seagrass productivity but may also increase rates of grazing on these marine plants. Here we show that high CO2 / low pH conditions of OA decrease, rather than increase, concentrations of phenolic protective substances in seagrasses and eurysaline marine plants. We observed a loss of simple and polymeric phenolics in the seagrass Cymodocea nodosa near a volcanic CO2 vent on the Island of Vulcano, Italy, where pH values decreased from 8.1 to 7.3 and pCO2 concentrations increased ten-fold. We observed similar responses in two estuarine species, Ruppia maritima and Potamogeton perfoliatus, in in situ Free-Ocean-Carbon-Enrichment experiments conducted in tributaries of the Chesapeake Bay, USA. These responses are strikingly different than those exhibited by terrestrial plants. The loss of phenolic substances may explain the higher-than-usual rates of grazing observed near undersea CO2 vents and suggests that ocean acidification may alter coastal carbon fluxes by affecting rates of decomposition, grazing, and disease. Our observations temper recent predictions that seagrasses would necessarily be “winners” in a high CO2 world.

Structure of epiphyton communities on Lake Baikal submerged macrophytes

Abstract We carried out a first study of Lake Baikal epiphyton on six species of submerged macrophytes: Myriophyllum spicatum L., Potamogeton perfoliatus L., Potamogeton sp., Sparganium gramineum Georgi, Ceratophyllum demersum L., and Elodea сanadensis Michaux. We identified 70 epiphyton species and intraspecific taxa belonging to 3 phyla, viz. Ochrophyta, Cyanobacteria, and Chlorophyta. Nine species of Cyanobacteria were new records for Lake Baikal. Epiphyton communities differing in species composition and quantitative characteristics grew on diverse species of submerged macrophytes. High levels of species richness were recorded on Sparganiumgramineum and Potamogeton sp., whereas low diversity of epiphyton was observed on Myriophyllum spicatum and Elodea canadensis. A monodominant community was revealed on the invasive Elodea canadensis represented by Cocconeis placentula var. placentula. Specific characteristics of morphology of submerged macrophytes influenced the structural organization and quantitative development of epiphyton. Epiphyton abundance and biomass were higher on upper sections of most plants than on lower sections, probably because of canopy shading of macrophyte lower portions.

To share or not to share: clonal integration in a submerged macrophyte in response to light stress

The ability of clonal plant species to share resources has been studied in many experiments. The submerged macrophyte Potamogeton perfoliatus produces interconnected ramets within short time intervals and hence may or may not share resources with ramets growing in less favourable microhabitats. From a genet point of view, sharing with ramets growing under less favourable conditions might not be an optimal strategy when photosynthates could be used to establish other ramets growing under more favourable conditions. To analyse the plasticity in clonal integration of P. perfoliatus, we set up a factorial aquaria experiment with unshaded or shaded recipient ramets (offspring), which were connected to or separated from donor ramets (parents). Increased biomass production of offspring in parent–offspring systems compared with severed offspring in both light and shade showed that ramets share resources through clonal integration. The relative translocation to the first- and second-offspring generation was influenced by habitat quality: If first-offspring ramets grew in a shaded microhabitat, second-offspring ramets clearly profited. This may be at least partially because of the fact that resources are shifted from first-offspring to second-offspring ramets, indicating controlled senescence of the first-offspring. This complex sharing behaviour might be relevant when plants produce ramets within a dense patch of macrophytes, where support of a shaded ramet might not pay off.

Plant distribution can be reflected by physiological responses to salinity of three submerged macrophytes from the Modern Yellow River Delta

With 4 figures Abstract: Patterns of distribution vary greatly among species in the Modern Yellow River Delta, the largest es- tuarine wetland in China. Although salinity has been considered as the key factor determining plant distribution patterns in this delta, the intrinsic mechanisms accounting for distribution patterns are far from clear. To this end, three submerged macrophytes (Ceratophyllum demersum L., Potamogeton perfoliatus L. and Myriophyllum spica- tum L.) were grown in 0.2 (control), 1.2, 2.4 and 3.6 psu salinity waters. The relative growth rate (RGR), content of MDA (malondialdehyde) and activities of the enzymes (SOD - superoxide; POD - peroxidase; CAT - catalase; APX - ascorbate peroxidase) in leaves were investigated. The RGR of M. spicatum decreased only in the 3.6 psu treatment, while those of C. demersum and P. perfoliatus declined significantly with increasing salinity. Compared to the control, RGR of M. spicatum, C. demersum and P. perfoliatus decreased by 31.8 %, 78.5 % and 71.0 % while the MDA content increased by 12.0 %, 35.9 % and 28.3 % in the 3.6 psu treatment, respectively, indicating that M. spicatum had a higher salinity tolerance ability than the other two species. The activities of four antioxidative enzymes increased with increasing salinity in M. spicatum. However, for C. demersum and P. perfoliatus, the four antioxidative enzymes increased in the 0.2 to 2.4 psu treatments, but decreased subsequently in the 3.6 psu treat- ment except for the activities of SOD and APX in C. demersum. It is concluded that antioxidative enzymes can protect M. spicatum from oxidative stress under higher salinity, but that this mechanism is absent in C. demersum and P. perfoliatus.