Amphibious Plant Research Articles

Photochemical efficiency of amphibious plants in an intermittent lake

During the six month dry period in the intermittent lake Cerknica in 2003, fluorescence parameters in 14 amphibious plants were measured to estimate the possible disturbance to photosystem II. Environmental changes due to intermittence caused no evident irreversible damage, since the potential photochemical efficiency of the majority of species and forms remained close to the optimal value at 0.83. Actual photochemical efficiency varied, showing different levels of temporary stress. Sudden submergence of aerial forms caused little disturbance to PS II. The results revealed the acclimation of plants thriving in intermittent habitats that enabled continuous harvesting of solar energy.

Understanding the realised niche of an amphibious softwater plant, Eleocharis multicaulis

The West European amphibious plant Eleocharis multicaulis, characteristic of softwater lakes, is rare and endangered in many regions. The present study aimed to evaluate several presumed niche features suggested in syntaxonomic studies, to reveal other important niche variables affecting the cover of this species and to quantify these responses. A dataset of 724 environmental and vegetation variables was built from a survey of 59 plots in The Netherlands and Belgium. Discriminant analysis, Pearson goodness-of-fit calculations, weighted averages and presence profiles were used. We found that Eleocharis multicaulis performs best in base-poor environments with an or- ganic top layer and an established vegetation. The species is apparently N limited and profits from N input as long as NO3 - is dominant over NH4 + . A high atmospheric N deposition is detrimental, because the resulting strong acidification leads to dominance of NH4 + over NO3 - . Intense acidification in agricultural areas has probably been an important extinction factor in the recent past. We hypothesise that current variability of soil Si, a very good predictor for the species' performance, might reflect these acidifi- cation processes. This hypothesis is supported by the fact that Si is correlated with trophic status, which is likely higher in agricultural regions. Nowadays, Eleocharis multicaulis suffers from agricultural P, K and alkalinity inputs as well as reduced oxy- gen supply (e. g. by reduced water-level dynamics), all leading to a lower redox state. These factors could bring about competitive suppression by other species, a high NH4 + /NO3 - ratio and P mobilisation.

A morphometric study of three closely related taxa in the European Isoetes velata complex

Isoetes velata A. Braun is an amphibious plant with Mediterranean and Ibero-Atlantic distribution, showing marked morphological variability. Within the same geographical area, closely related restricted-range taxa are also present, including I. velata ssp. asturicense (restricted to mountainous areas of the north-west Iberian Peninsula) and I. boryana (restricted to the southern French Atlantic coast). These related taxa have unclear taxonomy and are both threatened. We performed a morphometric study of specimens of the three taxa. Our results suggest that I. velata ssp. asturicense is better considered as a distinct species, I. asturicense Laínz (Laínz), distinguishable from the other two taxa by mean megaspore length (N ≥ 30) < 360 µm. In contrast, our results do not support consideration of I. boryana as a separate species, and we here propose that this taxon be considered as a variety, I. velata A. Braun var. boryana M.I. Romero & C. Real stat. nov.

Sexual reproduction under fluctuating water levels in an amphibious plant Schoenoplectus lineolatus (Cyperaceae): a waiting strategy?

Sexual reproduction of an amphibious macrophyte Schoenoplectus lineolatus (Fr. et Stav.) T. Koyama (Cyperaceae) was observed in three irrigation ponds with different water regimes in Hyogo Prefecture, western Japan. In each pond, inflorescence formation, flowering (anthesis), and seed set were recorded at three water depths (shallow, middle, and deep). Inflorescence formation was observed under submerged conditions in the three ponds. In Oku-ike Pond, anthesis was observed when the water level dropped in August and early September. Flowers opened after the emergence of the inflorescence into the air. In contrast, anthesis did not occur, despite inflorescence formation, in the other two ponds with no water level drop or a short period of water level drop. Submerged inflorescences could not set seeds unless pollination had already occurred in the air. Finally, inflorescence formation under submerged conditions was considered to be a waiting strategy for water drawdown in the irrigation ponds where marked water level decreases occur from summer to autumn. Anthesis can quickly start soon after the emergence of inflorescences.

Plant reproduction in temporary wetlands: the effects of seasonal timing, depth, and duration of flooding

In less predictable, drier climates depth, duration and season (month) of flooding influence not only germination and establishment of wetland plants but also completion of the life cycle through to sexual or asexual reproduction. A tank trial was carried out to investigate the effects of season (summer, autumn), duration (0–16 weeks) and depth of flooding (0–60 cm) and their interactions on sexual reproduction of a range of aquatic plant species. Seed bank material was collected from four New England wetlands in New South Wales, Australia. The majority of species germinating and establishing in the summer experiment were able to flower and set seed. In contrast, few of the plants growing during autumn had flowered after 16 weeks and biomass production was significantly reduced. For obligate submerged species flooding duration must be long enough to allow reproductive organs to form and for fertilisation and seed maturation to occur. Amphibious plants, in contrast, in particular those that respond morphologically to water presence or absence, had inflorescences emerging under a wide range of conditions, i.e. out of the water column when submerged, damp or spending only a portion of the life cycle submerged. Terrestrials established in autumn only in the damp treatments. A significant correlation was found for the dominant species from the amphibious and submerged groups between plant biomass and the number of reproductive units produced. Hence, diaspore production of wetland species is often a function of biomass production.

A preliminary study of crassulacean acid metabolism (CAM) in the endangered aquatic quillwortIsoetes sinensis Palmer in China

Isoetes sinensis Palmer (Isoetaceae) is an aquatic or amphibious plant that is critically endangered in China. Previous studies have revealed the crassulacean acid metabolism (CAM)-like photosynthetic pathway occurs commonly in submerged leaves in genusIsoetes. Water chemistry parameters and the titratable acidity content of the plant extract were measured from samples obtained in the early morning (7∶00) and late afternoon (15∶00) from twoI. sinensis populations in China. One population occurs in the eulittoral zone of a freshwater tidal river at low elevation (134 m) and another occurs in a densely vegetated, high elevation (1 100 m) alpine shallow pool. Significant differences in pH and titratable acidity of the plant extract were detected between the morning and afternoon samples. These changes are associated with diurnal changes in water chemistry. Our results provide the first evidence for the existence of the CAM pathway in the East Asian endemicIsoetes sinensis Palmer. The magnitude of fluctuations in the titratable acidity of the plant extract may be correlated with the severe carbon limitation imposed on the plants by its aquatic habitat.

Species specificity of resistance to oxygen diffusion in thin cuticular membranes from amphibious plants

ABSTRACTCuticular membranes (CM) were isolated enzymatically from leaves of amphibious and submerged plants, and the oxygen permeability of aerial and aquatic CMs was compared using a specially constructed oxygen electrode. Their thicknesses were estimated from transmission electron micrographs of intact leaves. When dry CMs were moistened, the permeability of typical aerial CMs changed differently from that of typical aquatic CMs during the desiccation, apparently reflecting different internal structures. The cuticle thickness was mostly &lt; 100 nm, and the range of permeance values was 5–143 × 10−6 m s−1, corresponding to resistance values of 7–210 × 103 s m−1. The resistance of an aerial CM was always higher than that of an aquatic one from the same species. Only the aquatic CMs showed a weak proportionality between resistance and thickness. The relation between resistance and thickness varied from aquatic to aerial CMs in a species specific way.

Herbivory and growth in terrestrial and aquatic populations of amphibious stream plants

1. Many amphibious plant species grow in the transition between terrestrial and submerged vegetation in small lowland streams. We determined biomass development, leaf turnover rate and invertebrate herbivory during summer in terrestrial and aquatic populations of three amphibious species to evaluate advantages and disadvantages of aerial and submerged life.2. Terrestrial populations had higher area shoot density, biomass and leaf production than aquatic populations, while leaf turnover rate and longevity were the same. Terrestrial populations experienced lower percentage grazing loss of leaf production (average 1.2–5.1%) than aquatic populations (2.9–17.3%), while the same plant dry mass was consumed per unit ground area.3. Grazing loss increased linearly with leaf age apart from the youngest leaf stages. Grazing loss during the lifetime of leaves was therefore 2.4–3.1 times higher than mean apparent loss to standing leaves of all ages. The results imply that variation in density of grazers relative to plant production can account for differences in grazing impact between terrestrial and aquatic populations, and that fast leaf turnover keeps apparent grazing damage down.4. We conclude that the ability of amphibious plants to grow submerged permits them to expand their niche and escape intense competition on land, but the stream does not provide a refugium against grazing and constrains plant production compared with the terrestrial habitat.

Persicaria amphibia (L. ) Gray (Polygonum amphibium L.)

A versatile rhizomatous perennial, one of the rather few truly amphibious plants (Rodwell 1995), with aquatic and terrestrial forms so different that the uninitiated may think that they are different species (Lousley & Kent 1981). Aquatic form. Pale, branching rhizomes < 0.2 m deep in underwater substrate (Best & Dassen 1987), and < 2 m under water (Spence in Veg. Scot.), carry perennating buds that produce pliable, sparsely branching stems with vestigial leaves and rings of adventitious roots; interodes 5-40 cm (Arber 1920). Stems branch < 10 cm underwater, and bear alternate floating leaves: blades pliant, waxy, smooth, 4-10 cm long, 2-4 cm wide, lanceolate/narrow-ovate, margin entire or minutely toothed; petioles 2-8 cm, flexible. Ochreae entire, membranous, semitranslucent, secreting mucilage around axillary bud. In early summer, shoots surface with 1-3 aerial leaves and inflorescences. Peduncle glabrous or sparsely hairy + stalked glands; otherwise aquatic form entirely glabrous. Terrestrialform. + glabrous, glandular-hairy, finely to coarsely pubescent or appressed-hispid. Rhizomes < 50 cm deep produce procumbent/erect stems, 0.4-1 (-2) m, branching below, little-branching above; internodes 1-4 cm, nodes (+ root-precursors) swollen. Ochreae entire, green, hairs (if present) may exceed margin. Petioles + rigid, 0.5-1.5 cm, blades 4-14 cm long, 1-3 cm wide, more opaque, coarse and inflexible than in aquatic form, lanceolate, margin fine-toothed, immature/early leaves often with dark chevron-shaped blotches.

Plant distribution and abundance in relation to physical conditions and location within Danish stream systems

The distribution of obligate submerged plants, amphibious plants and terrestrial plants in streams was examined in relation to water depth, substrate and distance to the banks using univariate and mulitivariate analyses. The analyses were based on recordings in more than 40 000 quadrats (25×25 cm) in 208 unshaded sites in the predominantly small and shallow (<1.6 m) Danish streams. Also, the distribution of plant abundance and richness from the source to the outlet of the stream system was determined. The submerged plants in Danish streams include 87 terrestrial, 22 amphibious and 30 obligate submerged taxa. The distribution of plant types was mainly related to water depth and distance to the bank among the physical conditions, while the type of bottom substrate had no significant influence. Terrestrial plants and amphibious plants (excluding Sparganium emersum) dominated in shallow water near the bank, but declined rapidly with increasing depth and distance to the bank, reflecting the importance of dispersal by ingrowth from populations on the banks to the water among these plants. Accordingly, these two plant groups constituted a higher proportion of total plant abundance in small streams than large streams. S. emersum dominated on great depth and distance to the banks, probably reflecting the lengthwise dispersal of this species from upstream to downstream parts of the stream system, the tolerance of the species to weed cutting and the adaptation to grow at low light intensities. Obligate submerged plants dominated at intermediate depths and at all distances from the bank except from 0 to 50 cm. This distribution reflects the ability of these species to disperse lengthwise in streams and live permanently submerged. The species number of all species and obligate submerged plants was lower in the smallest stream sites compared to larger downstream sites, while there was no difference for terrestrial and amphibious plants. The downstream increase of submerged species can be explained by the increase of habitat area and the dispersal of plants with the current, implying that the species pool accumulates with distance from the source. This result is at variance with a maximum richness of submerged plant species predicted for intermediate-sized streams according to the River Continuum Concept developed for large North American streams having forested shallow upstream sections and unshaded, deep downstream sections both unsuitable to submerged plant growth. The results for Danish streams imply that both the longitudinal connection through the flowing water and the transversal connection to the local species on the banks are important for plant distribution in the streams.

Photosynthetic pathway diversity in a seasonal pool community

1. Photosynthetic pathway diversity was evaluated for the dominant species in a seasonally aquatic community in the south‐western USA using 14C pulse‐chase techniques. 2. Under submerged conditions, only about half of the species were clearly C3, three of the 15 dominants were CAM, one species was C4 and three were potentially assimilating carbon with both C3 and C4 fixation. 3. During the brief terrestrial stage in the life history of these amphibious plants, both the CAM and the C3 + C4 species switched to C3, whereas the C4 species did not switch. 4. Numerous variations were apparent; for example, the C4 species, while exhibiting a biochemical pathway indistinguishable from terrestrial C4 plants, lacked Kranz anatomy in the aquatic foliage. Also, despite well‐developed CAM in several species, others exhibited low‐level diel changes in acidity, apparently not indicative of CAM. 5. Species with C4 or CAM CO2 concentrating mechanisms lacked the capacity for bicarbonate uptake, an alternative CO2 concentrating mechanism found in certain C3 species in this community. 6. Rubisco/PEPC in aquatic foliage was higher in C3 species than in C4, CAM or putative C3 + C4 species. In the terrestrial phase, as expected, the switch from CAM or C3 + C4 to strictly C3 assimilation was associated with a substantial increase in Rubisco/PEPC. Quite unexpected, however, was the substantial increase in this ratio in terrestrial C3 foliage. It is hypothesized that submerged C3 plants utilize PEPC for recycling of respiratory CO2 and/or C4 phototrophism under field conditions of limited CO2 and O2 saturation, and this is lost in the terrestrial foliage.

Plant growth and photosynthesis in the transition zone between land and stream

Many plant species grow in the transition between land and water in unshaded lowland streams. Our objective was to determine the importance of exposure to air or water on photosynthesis, CO 2 conductance and relative growth rate in four common amphibious species in streams. Photosynthesis was 2–3 times higher in air than in stream water six-fold supersaturated with CO 2, because diffusive boundary layers constrained CO 2 fluxes much more in water than in air. Leaves acclimated to life in air or water by increasing CO 2 affinity during photosynthesis at rate-limiting concentrations due to changes in leaf surface conductance and stomatal density. Leaves grown in water had a 1.8–4.6 times higher CO 2 conductance than leaves grown in air, when both the leaf types were measured under water. Aerial leaves had a 1.3–1.6 times higher CO 2 conductance than aquatic leaves, when both were measured in air. Growth of amphibious plants was severely constrained by low CO 2 availability in air-equilibrated water, while CO 2 enrichment in water to 40-fold supersaturation stimulated plant growth without fully reaching the growth rates in air. The widespread CO 2 supersaturation of streams facilitates the successful development of submerged populations of amphibious plants, but terrestrial populations continue to support faster growth and denser plant stands.

Plants as amphibians

From the poles to the tropics flooding is a powerful discriminator in plant distribution. Although plants can be divided globally as to whether or not they are tolerant of high water tables, it does not follow that all flood-tolerant species achieve their ability to survive flooding by similar adaptations. Flooding implies a periodic but temporary rise of the water table, hence plants that live in such areas have an amphibious life style. Amphibious plants have to adjust, not only to inundation and the dangers of oxygen deprivation, but also to the eventual lowering of water tables and often sudden re-exposure to a fully aerated environment and the lack of the physical support that is provided by flooding. In this respect they are distinct from aquatic species that live constantly in water. It is often tacitly assumed that for amphibious species flooding is the stressed condition and non-flooding the norm. This pre-judgement is not appropriate, particularly as in many habitats the flooded condition predominates for a longer part of the year than the unflooded. For amphibians, re-adapting from the aquatic to the terrestrial habitat requires specialised adaptations, just as much as a change from unflooded to flooded. Many flood-tolerant species, including surface-rooting grasses and sedges, may not be tolerant of anoxia, and instead prevent the accumulation of an oxygen debt in submerged organs by aeration mechanisms, including oxygen diffusion through aerenchyma, thermally induced mass movement of air, and the elongation of submerged shoots. In other species, and particularly in perennial plants with buried perennating organs, flooding can impose prolonged periods of anaerobiosis (anoxia). Being able to survive such oxygen deprivation requires (1) energy reserves sufficient for cell maintenance, (2) the prevention of cytoplasmic acidosis under anoxia, and (3) the anaerobic mobilisation of starch reserves. Re-entry to the aerobic habitat is facilitated by (4) the dispersal and excretion of products that transfer hydrogen from anoxic or hypoxic tissues, either to the external environment, or to parts of the plant with access to oxygen, before the anaerobic tissues return to air, and (5) anti-oxidative activity to minimise post-anoxic injury.

Induction of Kranz Anatomy and C 4 -like Biochemical Characteristics in a Submerged Amphibious Plant by Abscisic Acid

Induction of Kranz Anatomy and C 4 -like Biochemical Characteristics in a Submerged Amphibious Plant by Abscisic Acid

Induction of kranz anatomy and C4-like biochemical characteristics in a submerged amphibious plant by abscisic acid

The amphibious leafless sedge Eleocharis vivipara develops C4-like traits as well as Kranz anatomy under terrestrial conditions, but it develops C3-like traits without Kranz anatomy under submerged conditions. When submerged plants are exposed to aerial conditions, they rapidly produce new photosynthetic tissues with C4-like traits. In this study, experiments were performed to determine whether abscisic acid (ABA), a plant stress hormone, could induce the formation of photosynthetic tissues with Kranz anatomy and C4-like biochemical traits under water in the submerged form. When the submerged plants were grown in water containing 5 &mgr;M ABA, they developed new photosynthetic tissues with Kranz anatomy, forming well-developed Kranz (bundle sheath) cells that contained many organelles. The ABA-induced tissues accumulated large amounts of phosphoenolpyruvate carboxylase, pyruvate orthophosphate dikinase, and NAD-malic enzyme at the appropriate cellular sites. The tissues had 3.4 to 3.8 times more C4 enzyme activity than did tissues of the untreated submerged plants. Carbon-14 pulse and carbon-12 chase experiments revealed that the ABA-induced tissues fixed higher amounts of carbon-14 into C4 compounds and lower amounts of carbon-14 into C3 compounds as initial products than did the submerged plants and that they exhibited a C4-like pattern of carbon fixation under aqueous conditions of low carbon, indicating enhanced C4 capacity in the tissues. This report provides an example of the hormonal control of the differentiation of the structural and functional traits required for the C4 pathway.

Photosynthetic Characteristics of an Amphibious C4 Plant, Eleocharis retroflexa ssp. chaetaria

Eleocharis retroflexa (Poir.) Urban ssp. chaetaria (Roem. & Schult.) T. Koyama, an amphibious leafless sedge, grows not only under terrestrial conditions but also under completely submerged aquatic conditions. We investigated the photosynthetic traits and structural features of the culms, which are the photosynthetic organs, in the terrestrial and submerged forms of this species and compared them with those of other amphibious species of Eleocharis which are known to change the photosynthetic modes. The culms of the terrestrial form had Kranz anatomy with well-developed Kranz (bundle sheath) cells and high levels of C4 enzyme activity typical of the NAD-malic enzyme (NAD-ME) subtype of C4 metabolism. They also had a δ 13C value typical of C4 plants, indicating that the terrestrial form fixes carbon through the C4 pathway. The culms of the submerged form had not only a Kranz-like anatomy but also revealed anatomical traits typical of leaves of submerged aquatic plants. The activities of the C4 enzymes in the submerged form were lower than those in the terrestrial form, but were still in the range typical of G4 plants, 14C pulse-12C chase experiments with the submerged form indicated that almost all of the fixed 14C was incorporated into G4 compounds, and subsequently the raioactivity was transferred into C3 compounds and sucrose. The submerged form showed no diurnal fluctuation in malate level. These data demonstrate that a C4 metabolism is operative even in the submerged form. This unique amphibious C4 plant provides an intriguing example of the physiological and ecological adaptability of C4plants.

Effects of drought and flooding on the reproduction of an amphibious plant, Ranunculus peltatus

Aquatic seedlings of Ranunculus peltatus Schrank were subjected to three levels of drought (dry, saturated and flooded) at two different phenological stages, vegetative stage and at onset of flowering. Changes in growth form, timing of flowering, number of flowers and fruits and the number of seeds per fruit were monitored to test the effect of drought on reproduction. Plants that were transferred to a terrestrial, but water-saturated, environment at a vegetative stage rapidly changed from an aquatic, spreading, elongated growth form to a prostrate growth form and produced only slightly fewer seeds per pot (86) than the flooded control plants (93). Total seed production was decreased by 1000 seeds per pot in both saturated treatments compared to the control treatment. There was no significant difference in total seed production between plants encountering drought at a vegetative or a flowering stage (2471 vs. 2348 seeds per pot). Plants subjected to air drying of the soil (no water added) at both phenological stages changed growth form, but flower, fruit and seed production was negligible. The fact that total seed production was still relatively high under water-saturated conditions at both phenological stages may explains partially why this species is successful in temporary marshes where drought often occurs during its lifecycle.

Transpiration does not control growth and nutrient supply in the amphibious plant Mentha aquatica

ABSTRACT Mentha aquatica L. was grown at different nutrient availabilities in water and in air at 60% RH. The plants were kept at 600 mmol m−3 free CO2 dissolved in water (40 times air equilibrium) and at 30 mmol m−3 CO2 in air to ensure CO2 saturation of growth in both environments. We quantified the transpiration‐independent water transport from root to shoot in submerged plants relative to the transpiration stream in emergent plants and tested the importance of transpiration in sustaining nutrient flux and shoot growth. The acropetal water flow was substantial in submerged Mentha aquatica, reaching 14% of the transpiration stream in emergent plants. The transpiration‐independent mass flow of water from the roots, measured by means of tritiated water, was diverted to leaves and adventitious shoots in active growth. The plants grew well and at the same rates in water and air, but nutrient fluxes to the shoot were greater in plants grown in air than in those that were submerged when they were rooted in fertile sediments. Restricted O2 supply to the roots of submerged plants may account for the smaller nutrient concentrations, though these exceeded the levels required to saturate growth. In hydroponics, the root medium was aerated and circulated between submerged and emergent plants to minimize differences in medium chemistry, and here the two growth forms behaved similarly and could fully exploit nutrient enrichment. It is concluded that the lack of transpiration from leaf surfaces in a vapour‐saturated atmosphere, or under water, is not likely to constrain the transfer of nutrients from root to shoot in herbaceous plants. Nutrient deficiency under these environmental conditions is more likely to derive from restricted development and function of the roots in waterlogged anoxic soils or from low porewater concentrations of nutrients.

Expression of C3 and C4 photosynthetic characteristics in the amphibious plant Eleocharis vivipara: structure and analysis of the expression of isogenes for pyruvate, orthophosphate dikinase.

Eleocharis vivipara, a unique leafless amphibious sedge, adopts the C4 mode of photosynthesis under terrestrial conditions and the C3 mode under submerged aquatic conditions. To analyze the molecular basis of these responses to the contrasting environments, we isolated and characterized two full-length cDNAs for a key C4 enzyme, pyruvate, orthophosphate dikinase (PPDK; EC 2.7.9.1). The isogenes for PPDK, designated ppdk1 and ppdk2, were highly homologous to one another but not identical. The PPDK1 protein, deduced from the nucleotide sequence of the cDNA, contained an extra domain at the amino terminus which, presumably, serves as a chloroplast transit peptide, while PPDK2 lacked this extra domain. It seems likely, therefore, that the ppdk1 and ppdk2 genes encode a chloroplastic and a cytosolic PPDK, respectively. Genomic Southern blot analysis revealed the existence of a small family of genes for PPDK in the genome of E. vivipara. Northern blot analysis indicate that both chloroplastic and cytosolic genes for PPDK are expressed simultaneously in the culms, a photosynthetic organ, of E. vivipara and that the pattern of expression of these genes differs between the growth forms.

Growth and Morphology of Scirpus lacustris and S. maritimus Seedlings as Affected by Water Level and Light Availability

1. Adults of the emergent macrophytes Scirpus lacustris ssp. lacustris (S.l. lacustris), S. lacustris ssp. tabernaemontani (S.l. tabernaemontani) and S. maritimus occur along a gradient in water depth from deep to shallow water. This study examined whether seedlings of these taxa respond differently to changing hydrological conditions. 2. Seedlings of both S. lacustris subspecies showed the highest relative growth rate (RGR) under terrestrial growth conditions, whereas S. maritimus did so under submerged growth conditions. In all three taxa, shading reduced the mean RGR of terrestrial seedlings more strongly than that of submerged ones. 3. Scirpus maritimus and S.l. tabernaemontani maintained an erect growth form under water, whereas S.l. lacustris produced numerous long, floating leaves. 4. Under terrestrial growth conditions the specific leaf area (SLA) did not differ between taxa. Under submerged growth conditions the SLA differed as follows: S.l. lacustris > S.l. tabernae montani > S. maritimus. Irrespective of taxon and water level, the SLA was increased by shading. 5. Growth of all three taxa was reduced considerably after seedlings were transferred from terrestrial to submerged growth conditions. This effect was stronger with increasing age of seedlings. When transferred the other way round, seedlings of S.l. tabernaemontani and S. maritimus adapted quickly to the terrestrial growth conditions, whereas the thin leaves of S.l. lacustris partly dried out. 6. It was concluded that although seedling establishment of all three Scirpus taxa will be most successful under terrestrial conditions, subsequent fluctuating water levels may act as a strong selective force. This may determine the distribution of Scirpus taxa along a gradient in water depth during seedling establishment. [KEYWORDS: emergent macrophytes; heterophylly; plant size; relative growth rate; shading; submergence Aquatic macrophytes; amphibious plants; photosynthesis;submergence; responses; carbon; assimilation; strategies; vegetation; ethylene]