Lobelia Dortmanna Research Articles

Precipitated iron and manganese plaques restrict root uptake of phosphorus in <i>Lobelia dortmanna</i>

Precipitated iron and manganese plaques restrict root uptake of phosphorus in <i>Lobelia dortmanna</i>

Nitrification and denitrification in the rhizosphere of the aquatic macrophyte Lobelia dortmanna L.

Nitrogen and O2 transformations were studied in sediments covered by Lobelia dortmanna L.; a combination of 15N isotope pairing and microsensor (O2, NO3−, and NH4+) techniques were used. Transformation rates and microprofiles were compared with data obtained in bare sediments. The two types of sediment were incubated in doublecompartment chambers connected to a continuous flow-through system. The presence of L. dortmanna profoundly influenced both the nitrification-denitrification activity and porewater profiles of O2, NO3−, and NH4+ within the sediment. The rate of coupled nitrification-denitrification was greater than sixfold higher in L. dortmnanna-vegetated sediment than in bare sediment throughout the light–dark cycle. Illumination of the Lobelia sediment reduced denitrification activity by ∼30%. In contrast, this process was unaffected by light–dark shifts in the bare sediment. Oxygen microprofiles showed that O2 was released from the L. dortmanna roots to the surrounding sediment both during illumination and in darkness. This release of O2 expanded the oxic sediment volume and stimulated nitrification, shown by the high concentrations of NO3− (∼30 µM) that accumulated within the rhizosphere. Both 15N2 isotope and microsensor data showed that the root-associated nitrification site was surrounded by two sites of denitrification above and below, and this led to a more efficient coupling between nitrification and denitrification in the Lobelia sediment than in the bare sediment.

Diel Pulses of O_2 and CO_2 in Sandy Lake Sediments Inhabited by Lobelia Dortmanna

Lobelia dortmanna is a common representative of the small isoetid plants dominating the vegetation on sandy sediments in nutrient—poor softwater lakes in North America and Europe. We report here the discovery of pronounced depth profiles and pulses of dissolved O2 and CO2 in the pore—water of vegetated sediments between light and darkness. Pulses of O2 and CO2 were extensive in the upper sediment layers of high root density, because Lobelia roots absorb CO2 and release O2 during photosynthesis but absorb O2 and release CO2 during respiration, whereas fluxes across leaf surfaces are impeded by a cuticle of low gas permeability. Release of most O2 from the roots during Lobelia photosynthesis leads to O2 concentrations close to saturation in the root zone and O2 penetration to great sediment depth because of low microbial O2 consumption rates. The CO2 concentrations in the root zone of the most nutrient—poor sediments examined here (0.37—0.71 mmol/L) were below the levels required to saturate Lobelia photosynthesis (>3 mmol/L), and experimental enrichment with CO2 stimulated the development of higher O2 concentrations in the root zone. Cycles of O2, CO2 and nutrients are, therefore, intimately coupled in the Lobelia—sediment system, in contrast to terrestrial and other aquatic plants, where gas and nutrient fluxes are physically separated between leaves and roots and their respective surrounding media. The release of O2 from the roots should ensure efficient aerobic degradation or organic matter, lead to oxidized forms of Fe, Mn, and N, and can supply O2 to mycorrhizal fungi and an aerobic fauna associated with the roots.

An individual's status in populations of isoetid species

Individual size and fecundity of Isoetes lacustris L., Lobelia dortmanna L. and Littorella uniflora (L.) Aschers., were studied in relation to the depth gradient of an oligotrophic lake. The plants examined included individuals growing in the central part of the population habitat and in the deep and shallow border zones. Zone-related variation in population habitat and structure over the depth gradient has been demonstrated. The Isoetes population is strcturally divided into central and shallow-water zones; the Lobelia population into central and deep zones; the Littorella population into shallow and wave-disturbed, as well as into deep border zones. Isoetes individuals in the cental zone of the habitat have a rosette size of 87.1±37.8 cm 2, root length of 10.9±3.6 m and 839±422.6 macrospores. Corresponding figures in the shallow, non-disturbed zone are 116.8±47.1 cm 2, 17.5±6.6 m and 2289.3±1167. Lobelia individuals in the central zone of the habitat have a rosette size of 10.6±4.1 Cm 2, root length of 5±1.9 m and 1065.3±24.6 seeds. Corresponding figures in the deepest zone are 17.2±6.8 cm 2, 5±2.1 m and 1213.5±245.6. A small group of large and fecund individuals whose growth cycle has taken place in the border zones play a significant role in the population regeneration process: Lobelia in the deep zone and Isoetes in the shallow area not disturbed by waves. In every population (and habitat) zone, fecundity is a function of individual size, and variation in size is always greater than variation in fecundity. There are more small individuals in a population than indicated by the normal distribution (Gauss curve). Distributions of individual size- and fecundity-defining characters are always positively skewed.

Massive expansion of Juncus bulbosus L. after liming of acidified SW Norwegian lakes

Isoetes-Lobelia clear water lakes in an ultraoligotrophic area of south-western Norway were studied. Most lakes in the area are acidified, with a vegetation dominated by small isoetids such as Lobelia dortmanna L., Littorella uniflora (L.) Aschers. and Isoetes lacustris L. After liming, however, dense stands of Juncus bulbosus L. often have developed, filling up the water layer completely at relatively shallow sites and resulting in suppression of the original vegetation. In this study a comparison is made between plant growth and physical and chemical properties of water and sediment pore water in six limed and five non limed ‘reference’ lakes. It appears that liming leads to a strong increase in CO 2 production and mobilisation of nitrogen, phosphorus and iron in the sediment. Probably as a result of the high mobilisation of iron and the increased iron cycle no increased levels of phosphate in the water layer occur. As a result the waters are still very clear after liming. The rooted macrophyte Juncus bulbosus can benefit from this situation, as it is able to take up nutrients from the sediment pore water by its roots. It is discussed that the success of Juncus bulbosus is not only caused by the increased carbon dioxide, phosphate and nitrogen levels in the sediment pore water (internal eutrophication), but also by the fact that the sediment becomes anoxic, leading to a decrease in nitrate concentrations and a very strong increase in ammonium levels. It is known from experimental studies that Juncus bulbosus can only reach a very high biomass at high carbon dioxide levels in combination with high ammonium concentrations.

Effects of acidification on macrophyte growth in the HUMEX Lake Skjervatjern, with special emphasis on sphagnum auriculatum

Transplantation experiments for the study of aquatic macrophyte growth and vitality were carried out in the HUMEX Lake Skjervatjern. Plants (preferentially indigenous) were transplanted to plastic pots in the acid-treated (A) basin and the control (B) basin. During the first phase of the experiment in 1991–1992, shortly after start of acidification treatment, the following trends were apparent: 1) The isoetid plants ( Isoetes lacustris, Littorella uniflora, and Lobelia dortmanna) showed similar growth and vitality responses in the two Skjervatjern basins. 2) The elodeid species showed a slightly different response in the two basins. Juncus bulbosus exhibited a slightly higher growth rate in the acidified A basin. Myriophyllum alterniflorum died out after less than a growing season in the treated basin A, while a few shoots survived in basin B. 3) The transplanted shoots of submerged Sphagnum auriculatum showed throughout both growing seasons a distinctly higher growth rate in the B basin as compared with the acidified A basin. The submerged moss species Sphagnum auriculatum showed a decreased growth in the acidified basin less than a year after start of treatment. This contrasts the results of other lake acidification studies where submerged Sphagnum mats were found to increase. The decreased growth of Sphagnum auriculatum after treatment seems most probably to be due to the increased SO 4 concentrations, or to increased competition with epiphytic green algae.

Adaptations of Submerged Lobelia dortmanna to Aerial Life Form: Morphology, Carbon Sources and Oxygen Dynamics

Lobelia dortmanna is a vascular macrophyte of the isœtid life form which grows in sandy sediments of nutrient-poor lakes and may become exposed to the air during summer months. Both land and water forms of Lobelia have short stiff leaves which lack stomata and are covered by a thick cuticle providing high resistance to gas exchange and water loss. Incessant large air lacunae run between leaf and root.tips. With the leaves exposed to atmospheric air, both life forms absorb virtually all CO 2 by the roots from the CO 2 -rich sediments (ca 30 times air level) and release a substantial proportion of the O 2 produced during photosynthesis (...)

Classification of South Swedish Isoetid vegetation with the help of numerical methods

Releves of Isoetid vegetation from 60 lakes in southern Sweden have been classified with the help on numerical methods. A community system is constructed, at the variant level by clustering with the TABORD program, and at the community and subcommunity levels by reference to traditional floristic characteristics. The diagnostic species were selected with the help of PCA. Isoetes lacustris, Lobelia dortmanna and Littorella uniflora determined the community composition together with Eleocharis acicularis. The differentation of the syntaxa along the first three ordination axes of a PCA was clear. The complex water depth factor determines clearly the position of the small syntaxa (variants) in the PCA ordination space. At high levels of similarity the releves were grouped effectively with the TABORD program, so that the clusters are floristically homogeneous and easy to identify on the basis of floristic-sociological criteria. At higher syntaxon levels a selective use of diagnostic species was made.

Comparison of the macrophyte communities of a clearwater and a brownwater oligotrophic lake in Kejimkujik National Park, Nova Scotia

Beaverskin and Pebbleloggitch Lakes are small, proximate, acidic, oligotrophic, headwater lakes located in southwestern Nova Scotia. Beaverskin Lake has clear water, its euphotic zone is deep, and it has extensive beds of macrophytic vegetation that cover most of its bottom to a depth of 6.5 m. In contrast, the water of Pebbleloggitch Lake is highly colored by dissolved humic substances, and macrophytes are restricted to a narrow littoral fringe in depths of less than about 1.8 m. The most widespread macrophyte community in Beaverskin Lake occurs at depths of 2.0–6.5 m and is dominated by Sphagnum macrophyllum and Utricularia vulgaris, while the second most prominent community is littoral and is dominated by Eriocaulon septangulare, Lobelia dortmanna, and Eleocharis acicularis. The most prominent community in Pebbleloggitch Lake is dominated by the floating-leaved Nuphar variegatum rooted as deep as 1.8 m, while communities dominated by E. septangulare and Sphagnum spp. occur in water less than about 0.7 m deep.

The role of CO2 uptake by roots and CAM in acquisition of inorganic C by plants of the isoetid life-form: a review, with new data on Eriocaulon decangulare L.

The isoetid life-form was originally defined on morphological grounds; subsequent physiological investigations showed that all of the isoetids examined took up a large fraction of the inorganic C fixed in their leaves from the root medium under natural conditions, and that some of them carried out much of their assimilation of inorganic C via a CAM-like mechanism. Root-dominated uptake of inorganic C appeared to be unique to, and ubiquitous in, the isoetids. I However, a large capacity for CAM-like metabolism in submerged vascular plants is not universal in isoetids, nor is it restricted to this life-form, being also found in Crassulaa aquatica. The work described here shows that submerged specimens of the North American Eriocaulon decangulare have a high fraction of their dry weight in the root system, a trait characteristic of isoetids but uncommon in other submerged vascular plants. E. decangulare has vesicular-arbuscular mycorrhizas, as do other flowering plant isoetids hut not, generally, submerged Isoetes spp. Under conditions of natural supply of inorganic C, E. decangulare, like other isoetids, takes up most of its inorganic C through its roots. Uptake of inorganic C by both roots and shoots involves CO2 rather than HCO3 : photosynthesis at high external pH values does not exceed the rate of uncatalysed HCO3 - to CO2 conversion in the medium and there is no detectable extracellular carbonic anhydrase activity. Measurements of titratable acidity and of malate content of leaves sampled at dawn and at dusk showed that E. decangulare, growing and tested under either emersed or submersed conditions, did not exhibit CAM-like behaviour. CAM was also absent from three non-isoetid aquatic macrophytes (Amphibolic antarctica, Eeklonia radiata and Vallisneria spiralis) which were examined. E. decangulare thus resembles all other isoetids tested in acquiring much of its inorganic C via the root system. E. decangulare also resembles most of the isoetids which are not members of the Isoetaceae (e.g.) E. septangulare, Lobelia dortmanna and Subularia aquatica) but differs from submerged Isoetaceae and Littorella uniflora in lacking CAM. The ecological significance of uptake of CO2 via the roots and, where it occurs, of CAM in isoetids may be related to either inorganic C or, via improved N use efficiency, inorganic C as a limiting resource. The isoetid life-forms has evolved independently in at last five different families of vascular plants; it probably derived fairly immediately from terrestrial or amphibious ancestors with a similar rosette form. Emergent Isoetaceae with acquisition of CO2 via roots and CAM probably evolved from submerged isoetids. CONTENTS Summary 123 I. Introduction 126 II. Material and Methods 127 III. Results and Discussion 129 IV. Conclusions 142 Acknowledgements 142 References 143.

The macrophytes in lake Änketjärn—a lake dominated by Juncus bulbosus L

AbstractThe distribution of macrophytes and the biomass development during the summer was studied in the slightly acidified Lake Änketjärn in western Sweden. The submerged cyperid Juncus bulbosus, which has been reported to expand in acidifying lakes, covered almost 50% of the lake area. The most dense Juncus vegetation was found at 1.5 m on loose, highly organic sediment. Besides J. bulbosus the vegetation was characterized by Nympheids, Carex rostrata and C. lasiocarpa (approximately equally important in the stands), Equisetum fluviatile and Lobelia dortmanna, species which showed a quite distinct zonation with depth.

Flowering, Germination and Zonation of the Submerged Aquatic Plant Lobelia Dortmanna L.

SUMMARY (1) Lobelia dortmanna L. was studied in some Scottish lochs. It flowered from May to October. The number of flowers per plant was greater in less exposed sites. Larger plants were more likely to flower and small plants did not flower. Plants flowered to the depth limit in one loch, producing totally submerged flowers. These results are discussed with reference to current hypotheses of resource allocation. (2) Almost all capsules set seeds, most of which were viable (including those of submerged flowers). Seeds sank quickly and become buried up to 10-mm deep in the loch sediment. A cold-stratification period was found to be necessary before germination and seeds could survive both drying and freezing. Germination could proceed over a 1 5-25?C temperature range, though below 20?C rates were low. The seeds required light for germination, with some evidence of red promotion and far-red inhibition. Germination could also take place at very low light levels (PAR=4 ,umol photons m-2 s-'). Anoxia induced a secondary dormancy that required further cold-stratification to break it. (3) Seedlings in culture were unable to survive at the low light intensities that permitted germination. (4) In the lochs, sufficient light was available to allow germination well below the observed zonation limits of L. dortmanna. Light was rapidly absorbed by the sediment so some buried seeds would be unable to germinate. (5) The vertical zonation of this species is not controlled by seed germination requirements, but by the inability of plants to grow at the low light levels in deeper water.

Utilization of Sediment CO2 by Selected North American Isoetids

The photosynthetic uptake of root-zone CO2 was determined for Eriocaulon septangulare, Gratiola aurea, Isoetes macrospora, Littorella uniflora var. americana and Lobelia dortmanna as part of a study of the photosynthetic carbon economy of submerged aquatic isoetids. The pH and dissolved inorganic carbon (DIC) of the sediment interstitial water in four Wisconsin lakes reflected the water column character, where the DIC increased with depth in the sediment to concentrations five to ten times those of the water column. Sediment free CO2 concentrations were 5–50 times those in the water column and were similar at all sites (about 05–1.0mM CO2 in the root-zone). In ‘pH-drift’ studies these plants were unable to take up HCO2−. Laboratory determinations of the carbon uptake from the root and shoot-zones were made for all five species. These experiments showed that CO2 in the root-zone accounted for 65–95 per cent of external carbon uptake for the five species. For G. aurea and E. septangulare, root-zone CO2 was > 85 per cent of carbon uptake.

ENVIRONMENTAL CONTROL OF THE SEASONAL GROWTH OF THE SUBMERSED AQUATIC MACROPHYTE LOBELIA DORTMANNA L.

SUMMARYLeaf growth, photosynthesis and soluble carbohydrate content were measured for Lobelia dortmanna L. across one year in a small oligotrophic lochan in the northwest of Scotland at a number of sites, varying in degree of exposure, sediment type, nutrient concentrations and plant form. Leaf production and loss occurred during the entire year, although production and photosynthesis were maximal in the early summer. Soluble carbohydrate was highest in the early spring, and was lowest when leaf production was greatest. Environmental changes (solar irradiance, lochan temperature and water levels) were also related to growth rates, showing a particularly strong correlation between irradiance and the relative leaf growth rate. Little influence of epiphytes or limitation of growth by nutrient or the contribution of inorganic carbon was found.

Ammonium and nitrate uptake by aquatic plants from poorly buffered and acidified waters

In the Netherlands, atmospheric deposition of ammonia compounds, particularly ammonium sulphate, is an important source for the acidification of oligotrophic soft waters. As a consequence, the acidified waters are generally nitrogen enriched, ammonium being the dominant N form. In this study, it is examined how this alteration in the nitrogen household affects the aquatic plant communities in acidifying waters. The uptake of ammonium and nitrate by leaves and roots of two groups of freshwater plants has been studied using glass incubation chambers. The forst group ( Littorella uniflora (L.) Aschers.; Lobelia dortmanna L.; Luronium natans (L.) Raf.; Echinodorus ranunculoides (L.) Engelm.) is characteristic of nitrogen-poor soft waters, whereas the second group ( Juncus bulbosus L.; Sphagnum flexuosum Dozy & Molk.; Agrostis canina L.; Drepanocladus fluitans (Hedw.) Warnst.) often occurs in dense stands in nitrogen-enriched, acid waters. Both groups have typical adaptations to the nitrogen condition of their aquatic environment. The soft-water species show a nitrate-dominated (63–73%) nitrogen utilization, with the roots as the major (83%) uptake site. Moreover, they are able to survive at very low nitrogen concentrations. The acid-tolerant species have an ammonium-dominated (85–90%) nitrogen utilization, with the leaves as the major (71–82%) uptake site. This group profits from the increased ammonium levels in acid waters. It is concluded that in the case of acidification increased ammonium concentrations additionally account for the suppression of typical soft-water communities by communities dominated by Juncus bulbosus and Sphagnum spp.

Aquatic plants of acid lakes in Kejimkujik National Park, Nova Scotia; floristic composition and relation to water chemistry

To document the aquatic flora of acid lakes in Kejimkujik National Park, N.S., the presence and abundance of aquatic macrophytes growing in water deeper than 3 dm were recorded in 20 lakes. Of the 45 species found, the most important were Sphagnum macrophyllum, Eriocaulon septangulare, Utricularia purpurea, Scirpus subterminalis, Pontederia cordata, Nuphar variegatum, Nymphaea odorata, Eleocharis acicularis, Sparganium angustifolium, Potamogeton confervoides, Lobelia dortmanna, Potamogeton epihydrus, and Utricularia vulgaris. To explore the relationship between floristic composition and water chemistry, information on 12 chemical variables and colour was related to species presence–absence using a nonparametric test based on relative neighbourhood graphs. Analyses of variance (ANOVAs) using chemical data and six groups suggested by a conditional clustering of the species presence–absence data demonstrated significant heterogeneity in Ca, pH, and HCO3. Furthermore, these three proved to be highly correlated. A canonical variate analysis of the six groups revealed one significant axis and separated the lakes into two major groups, characterized by relative acidity. An ANOVA of these two groups established that colour was also significant. There were fewer species in the more acidic (range 8–20, average 15) than in the less acidic lakes (range 15–32, average 22).

The growth strategies and distribution of isoetids in Scottish freshwater lochs

The isoetids are one of the commonest ecological groupings of aquatic macrophytes in Scotland. Their growth strategies involve a range of features associated with Grime's classification of plant strategies. Subularia aquatica L. is a characteristic ruderal, although all of the isoetids occur in habitats that are disturbed. Littorella uniflora (L.) Aschers. and Isoetes lacustris L. are relatively stress tolerant with respect to low light. Littorella uniflora is also better able to withstand competition than the other isoetids. All are stress tolerant when considering growth form and the nutrient limitation of the habitats in which they commonly occur. Littorella uniflora has a much wider range of distribution than the other isoetids with regard to alkalinity or nutrient status of any loch. An experimental growth study confirmed that Littorella uniflora is faster growing and has a greater response to increasing nutrients than Lobelia dortmanna L., and this is used to explain its greater tolerance of mesotrophic environments. Decline of the isoetids in Scotland is found to be due to drainage, reservoir construction, acidification and eutrophication. The latter factor is thought to be the most important, although evidence on these factors is limited. This is discussed in relation to the growth strategies of these plants.

Responses of the Lobelia-epiphyte complex to liming of an acidified lake

The rates of radiocarbon uptake and chlorophyll content of the Lobelia-epiphyte complex were studied in the acidified (pH 4.2–4.7) lake, Gårdsjön, Sweden. Before liming and one and three years after liming estimates were made for Lobelia dortmanna L. leaves with epiphyton and for leaves without epiphyton. Chlorophyll content of the leaf segments without epiphyton was lowest in acidic conditions and highest in the third year after liming. Epiphytic 14CO 2-uptake was significantly higher in acidic conditions and was positively correlated with the chlorophyll content of corresponding segments of leaves with epiphyton. Liming induced changes in the species composition and biomass of the phytoplankton and reduced epiphytic cover.

Aquatic angiosperm communities from lochs on Rhum

Summary The plant communities from twenty lochs and lochans on Rhum are surveyed. Species lists are given for each site. Aquatic vegetational cover is sparse and only a limited number of plant communities are present, predominantly those involving Lobelia dortmanna and Littorella uniflora as dominants or co-dominants, and a more restricted representation of communities with Equisetum fluviatile, Phragmites australis or Nymphaea alba subsp. alba. Exposure and poor substratum are suggested as factors causing limited plant growth. This work is discussed in the light of other studies carried out in Scotland.

Epiphyte shading and its effect on photosynthesis and diel metabolism of Lobelia dortmanna L. during the spring bloom in a danish lake

A dense epiphyte community develops on Lobelia dortmanna L. during spring in the mesotrophic waters of Lake Almind, Denmark. This community has attenuated the incident light at 0.5 m depth by 67.4–81.7% within two years. The attenuation is spectrally selective, the proportion of red light transmitted increasing with epiphyte density. Epiphyte attenuation reduces the photosynthesis of Lobelia by increasing the light-compensation point and the saturation light intensity at the surface. These effects are predictable from epiphyte attenuations measured in suspensions scraped from the leaves of Lobelia and on the basis of photosynthesis—light relationships. Epiphyte attenuation and reduction of Lobelia photosynthesis are proportional in low light intensities (i.e., low surface light and/or high epiphyte attenuation) and independent in saturation light. The estimated light-compensation point for diel metabolism of Lobelia during spring was 3.33–3.66 E m −2 day −1 at 0.5 m depth, close to the natural level in the lake. This suggests that Lobelia grows only slowly during spring and resumes growth subsequently during summer and autumn, when epiphyte density decreases due to N and P limitation. The depth limit of Lobelia was found to be 1.0 m. Without epiphyte attenuation, the daily light-compensation point during spring would occur at 3.5 m. This supports the view that epiphyte attenuation may be important as concerns the seasonal growth and depth penetration of host macrophytes.