Triglochin Maritima Research Articles

Response of a subarctic salt marsh plant community to foraging by captive lesser snow geese

Foraging intensity and faecal inputs are important determinants of plant community response to herbivory. We used captive adult lesser snow geese (Anser caerulescens caerulescens), which feed on both above- and below-ground plant tissues, to manipulate foraging intensity and faecal inputs to plots in a sedge meadow in spring, 1996. We measured plant and soil characteristics throughout the growing season of 1996 and in August 1997. We analysed three contrasts: grazed plots versus ungrazed controls, plots with a short period of feeding (3 goose-hours) versus plots with a long period of feeding (6 goose-hours), and grazed plots with faeces versus grazed plots without faeces. Although grazed plots had an order of magnitude higher foraging intensity than that imposed by wild geese in the marsh, there was no effect of feeding on biomass or nitrogen concentration in the dominant species, Carex ramenskii and Triglochin maritimum, after one and two growing seasons. The amount of forage removed by geese did not differ between plots grazed for long and short periods, indicating that geese were able to remove little additional biomass after 3 hours due to low availability. Therefore, the amount of biomass removed by geese was a better indicator of foraging intensity than the time geese fed on plots. The presence of faeces had no effect on biomass or nitrogen concentration in Carex ramenskii or Triglochin maritimum, or on rates of net nitrogen mineralization in soils. Thus, faeces did not appear to increase nitrogen availability for plants in this marsh, probably because faecal density was low.

Seed Germination of Triglochin Maritima as Influenced by Salinity and Dormancy Relieving Compounds

Triglochin maritima had only 40 % germination in distilled water, but germination was substantially enhanced when seeds were exposed to ethephon, fusicoccin, proline, kinetin, and thiourea. Also, the effect of low salinity on germination was alleviated by fusicoccin, kinetin, nitrate and thiourea, whereas, the reduction in germination at high salinity was partially countered by ethephon, kinetin, thiourea and nitrate.

Effects of migratory geese on plant communities of an Alaskan salt marsh

SummaryWe studied the effects of lesser snow geese (Anser caerulescens caerulescens) and Canada geese (Branta canadensis) on two salt marsh plant communities in Cook Inlet, Alaska, a stopover area used during spring migration. From 1995 to 1997 we compared plant species composition and biomass on plots where geese were excluded from feeding with paired plots where foraging could occur.Foraging intensity was low (650–1930 goose‐days km−2) compared to other goose‐grazing systems.Canada geese fed mainly on above‐ground shoots ofTriglochin maritimum, Puccinelliaspp. andCarex ramenskii, whereas the majority of the snow goose diet consisted of below‐ground tissues ofPlantago maritimaandTriglochin maritimum.Plant communities responded differently to goose herbivory. In the sedge meadow community, where feeding was primarily on above‐ground shoots, there was no effect of grazing on the dominant speciesCarex ramenskiiandTriglochin maritimum. In the herb meadow community, where snow geese fed onPlantago maritimaroots and other below‐ground tissues, there was a difference in the relative abundance of plant species between treatments. Biomass ofPlantago maritimaandPotentilla egediiwas lower on grazed plots compared with exclosed, whereas biomass ofCarex ramenskiiwas greater on grazed plots. There was no effect of herbivory on total standing crop biomass in either community. The variable effect of herbivory onCarex ramenskiibetween communities suggests that plant neighbours and competitive interactions are important factors in a species’ response to herbivory. In addition, the type of herbivory (above‐ or below‐ground) was important in determining plant community response to herbivory.Litter accumulation was reduced in grazed areas compared with exclosed in both communities. Trampling of the previous year’s litter into the soil surface by geese incorporated more litter into soils in grazed areas.This study illustrates that even light herbivore pressure can alter plant communities and affect forage availability.

Restoring the Vegetation of Mined Peatlands in the Southern Rocky Mountains of Colorado, U.S.A.

AbstractSouth Park is a high‐elevation, semi‐arid, treeless intermountain basin in central Colorado. A few extreme rich fens occur on the western margin and in the center of South Park where regional and local groundwater flow systems discharge to the ground surface. Over the past 40 years there has been extensive peat mining in these fens, but restoration methods have yet to be developed and successfully applied. The first part of this study compared the naturally reestablished vegetation on six mined peatlands with six pristine sites, while the second part of the study tested different revegetation techniques in 27 plots with varying depths to the water table. The six mined sites had only 30 plant species as compared with 122 species in the unmined sites; 43% of the species in the mined sites were not present in the undisturbed fens. Even after 40 years the sedges and willows that dominate the undisturbed sites were largely absent on the mined sites. The revegetation experiments seeded eight species, transplanted Carex aquatilis (water sedge) seedlings, transplanted rhizomes from six species, and transplanted four species of willow cuttings. Of the eight species seeded, only Triglochin maritima (arrowgrass) germinated and established seedlings. C. aquatilis seedlings, rhizome transplants of C. aquatilis, Kobresia simpliciuscula (elk sedge), and Juncus arcticus (arctic rush), and willow cuttings all had differing patterns of survival with respect to the annual maximum height of the water table. These results indicate that the dominant species can be successfully reintroduced to mined surfaces with the appropriate hydrologic conditions, but human intervention will be necessary to rapidly re‐establish these species. The slow rate of peat accumulation means that restoration of the mined fens will require hundreds, if not thousands, of years.

Cloning and expression of cytochrome P450 enzymes catalyzing the conversion of tyrosine to p-hydroxyphenylacetaldoxime in the biosynthesis of cyanogenic glucosides in Triglochin maritima.

Two cDNA clones encoding cytochrome P450 enzymes belonging to the CYP79 family have been isolated from Triglochin maritima. The two proteins show 94% sequence identity and have been designated CYP79E1 and CYP79E2. Heterologous expression of the native and the truncated forms of the two clones in Escherichia coli demonstrated that both encode multifunctional N-hydroxylases catalyzing the conversion of tyrosine to p-hydroxyphenylacetaldoxime in the biosynthesis of the two cyanogenic glucosides taxiphyllin and triglochinin in T. maritima. This renders CYP79E functionally identical to CYP79A1 from Sorghum bicolor, and unambiguously demonstrates that cyanogenic glucoside biosynthesis in T. maritima and S. bicolor is catalyzed by analogous enzyme systems with p-hydroxyphenylacetaldoxime as a free intermediate. This is in contrast to earlier reports stipulating p-hydroxyphenylacetonitrile as the only free intermediate in T. maritima. L-3,4-Dihydroxyphenyl[3-(14)C]Ala (DOPA) was not metabolized by CYP79E1, indicating that hydroxylation of the phenol ring at the meta position, as required for triglochinin formation, takes place at a later stage. In S. bicolor, CYP71E1 catalyzes the subsequent conversion of p-hydroxyphenylacetaldoxime to p-hydroxymandelonitrile. When CYP79E1 from T. maritima was reconstituted with CYP71E1 and NADPH-cytochrome P450 oxidoreductase from S. bicolor, efficient conversion of tyrosine to p-hydroxymandelonitrile was observed.

Effects of resource competition and herbivory on plant performance along a natural productivity gradient

Summary 1 The effects of resource competition and herbivory on a target species, Triglochin maritima, were studied along a productivity gradient of vegetation biomass in a temperate salt marsh. 2 Transplants were used to measure the impact of grazing, competition and soil fertility over two growing seasons. Three parts of the marsh were selected to represent different successional stages; Triglochin reached local dominance at intermediate biomass of salt‐marsh vegetation. At each stage, three competition treatments (full plant competition, root competition only, and no competition) and three grazing treatments (full grazing, no grazing on Triglochin, and no grazing on Triglochin or neighbours) were applied to both seedlings and mature plants. 3 Competition and herbivory reduced biomass and flowering of Triglochin. The impact of grazing was strongest at the stage with the lowest biomass, while both herbivory and competition had a significant impact at the stage with the highest biomass. When plants were protected from direct herbivory, competition operated at all three successional stages. 4 Grazing reduced light competition when vegetation biomass was low or intermediate, but at high biomass there was competition for light even when grazing occurred. Herbivore exclusion increased the effects of plant competition. Except at low biomass, the negative impact of plant competition on Triglochin performance was greater than the positive effect of not being grazed. 5 Grazing played a minor role in seedling survival and establishment which were largely controlled by competitive and facilitative effects. 6 Once established, the persistence of Triglochin will be determined largely by grazing. Intense grazing in the younger marsh and increasing competition for light in the older marsh will restrict the distribution to sites with intermediate biomass.

Biosynthesis of Cyanogenic Glucosides in Triglochin maritima and the Involvement of Cytochrome P450 Enzymes

The biosynthesis of the two cyanogenic glucosides, taxiphyllin and triglochinin, in Triglochin maritima (seaside arrow grass) has been studied using undialyzed microsomal preparations from flowers and fruits. Tyrosine was converted to p-hydroxymandelonitrile with Vmax and Km values of 36 nmol mg−1 g−1 fresh weight and 0.14 mM, respectively. p-Hydroxyphenylacetaldoxime and p-hydroxyphenylacetonitrile accumulated as intermediates in the reaction mixtures. Using radiolabeled tyrosine as substrate, the radiolabel was easily trapped in p-hydroxyphenylacetaldoxime and p-hydroxyphenylacetonitrile when these were added as unlabeled compounds. p-Hydroxyphenylacetaldoxime was the only product obtained using microsomes prepared from green leaves or dialyzed microsomes prepared from flowers and fruits. These data contrast earlier reports (Hösel and Nahrstedt, Arch. Biochem. Biophys. 203, 753–757, 1980; and Cutler et al., J. Biol. Chem. 256, 4253–4258, 1981) where p-hydroxyphenylacetaldoxime was found not to accumulate. All steps in the conversion of tyrosine to p-hydroxymandelonitrile were found to be catalyzed by cytochrome P450 enzymes as documented by photoreversible carbon monoxide inhibition, inhibition by antibodies toward NADPH-cytochrome P450 oxidoreductase, and by cytochrome P450 inhibitors. We hypothesize that cyanogenic glucoside synthesis in T. maritima is catalyzed by multifunctional cytochrome P450 enzymes similar to CYP79A1 and CYP71E1 in Sorghum bicolor except that the homolog to CYP71E1 in T. maritima exhibits a less tight binding of p-hydroxyphenylacetonitrile, thus permitting the release of this intermediate and its conversion into triglochinin.

The effect of increasing salinity on the growth and ion content of three non-halophytic wetland macrophytes

Increasing salinisation is occurring over large parts of south-eastern Australia. This has potential to impact severely on the biodiversity of wetlands affected by rising saline groundwater and inundated by saline water discharged to rivers. Investigations have been made into the effect of salinities of 2, 2–6 (increased over 64 days) and 6 g NaCl l −1 on the growth, leaf demography and ion concentrations of three wetland macrophytes, Amphibromus fluitans, Potamogeton tricarinatus and Triglochin procera grown in greenhouse troughs. Potamogeton tricarinatus was the most severely affected showing significantly reduced dry weight and leaf size at 6 g l −1 along with a reduction in leaf appearance rate and an increase in leaf death. Triglochin procera was not as severely effected although leaf size was still reduced in 6 g l −1 treated plants. Amphibromus fluitans was unaffected by salinity. Na +, K + and Cl − ion contents were determined for leaves of different ages. The three species exhibited very different patterns of ion accumulation. Amphibromus fluitans excluded Na + and maintained a low concentration of Na + in younger leaves relative to older leaves. Potamogeton tricarinatus was saturated in uptake of Na + at all treatment levels. No leaf age effect was observed, with similar Na + concentrations in all leaves. The absence of a leaf age gradient may be attributable to a capacity to absorb Na + from the water column directly into the leaves irrespective of age. Na + K + ratios were lowest for A. fluitans with a strong leaf age gradient of increasing Na + K + ratio from younger to older leaves. Potamogeton tricarinatus was intermediate in Na + K + ratio but with no clear leaf age gradient. Whereas Na + K + ratios ranged from 2 to 8 for A. fluitans and 5 to 15 in P. tricarinatus, T. procera ranged from 5 in the youngest leaves to 35 in the oldest leaves. Triglochin procera like its halophytic relative, Triglochin maritima, had very high Na + K + ratios. Triglochin procera may be capable of absorbing Na + into leaf vacuoles which could be balanced by a high concentration of a compatible solute such as proline in the leaf cell cytoplasm.

Effects of light, salinity, and thermoperiod on the seed germination of halophytes

Seed germination of desert shrubs (Atriplex griffithii Moq., Haloxylon recurvum (Moq.) Bunge ex Boiss, Suaeda fruticosa (L.) Forssk., Triglochin maritima L.), and a forb (Zygophyllum simplex L.) was studied under various light, temperature, and salinity regimes. Seed germination of Atriplex griffithii, Z. simplex, and Suaeda fruticosa was least affected by light, whereas, seeds of H. recurvum and T. maritima had a light requirement for germination. Haloxylon recurvum seeds did not germinate at 10–20 °C in the dark, and no T. maritima seeds germinated in dark at all thermoperiod and salinity regimes studied. Seed germination was inhibited in all species with an increase in salinity, and this inhibition was more substantial in dark than in light. Key words: Atriplex griffithii, halophyte, Haloxylon recurvum, light, seed germination, Suaeda fruticosa, Triglochin maritima, thermoperiod, Zygophyllum simplex.

Effects of thermoperiod on recovery of seed Germination of Halophytes from Saline Conditions

Recovery of seed germination from NaCl salinity of desert shrubs (Haloxylon recurvum and Suaeda fruticosa, and the herbs Zygophyllum simplex and Triglochin maritima was studied under various thermoperiods. The percentage of ungerminated seeds that recovered when they were transferred to distilled water varied significantly with variation in species and thermoperiods. Zygophyllum simplex had little recovery from all NaCl concentrations in all thermoperiods. Haloxylon recurvum, S. fruticosa, and T. maritima showed substantial recovery. Percentage recovery was highest in S. fruticosa, followed by T. maritima, and H. recurvum. Thermoperiodic effects varied with the species investigated. There was little thermoperodic effect on the percentage recovery of S. fruticosa, except in the higher salinity treatment at higher thermoperiods. Variation in thermoperiod appears to play an important role in recovery of germination of halophytes from salt stress when seeds are transferred to distilled water.

Water and soil chemistry, floristics, and phytosociology of the extreme rich High Creek fen, in South Park, Colorado, U.S.A.

An extreme rich fen complex located in South Park, Colorado, is the most southern representative of this ecosystem type known in North America and the first described from the Southern Rocky Mountains. The fen is fed by ground water emerging from glacial outwash and has pH ranging from 7.6 to 8.3 and Ca2+ concentrations greater than 50 mg kg−1. The very low precipitation–evapotranspiration ratio in South Park causes Na+ and Mg2+ salts to accumulate in some soils, forming sodic peats that support halophyte communities. Character species of this fen include Kobresia simpliciuscula, Trichophorum pumilum, Carex scirpoidea, Carex microglochin, Carex livida, Utricularia ochroleuca, Triglochin palustris, Triglochin maritima, Salix Candida, Salix myrtillifolia, Salix serissima, Thalictrum alpinum, and Scorpidium scorpioides. A hierarchical classification of the vegetation is developed using numerical and table methods and includes 14 aquatic, peatland expanse, and salt flat communities. The most floristically similar fens occur in northern Ontario, northwestern Wyoming, and northern Montana. Keywords: peatland, extreme rich fen, South Park, Colorado, Rocky Mountains.

Utilization, diet and diet selection by brent geese Branta bernicla bernicla on salt‐marshes in Norfolk

The diet and utilization by brent geese of two plant communities (Limonium/Armeria marsh—a short sward community in the upper mid salt‐marsh and composed of several species, and Salicornia marsh—a community of the lower salt‐marsh dominated by Salicornia europuea agg. and Aster tripolium) were studied on the north Norfolk coast. The biomass on these communities was highest in autumn and declined markedly in November owing to the senescence and die‐off of the succulent species. This decline was not significantly precipitated by the grazing of the geese but coincided with their switch to inland habitats where the biomass m‐2 and total food available on fields of winter wheat and grassland within the population's home range was 20–30 times greater. Brent geese continued to graze salt‐marsh at a low intensity through the winter, feeding largely on Puccinellia maritima. In spring they returned largely to Limonium/Armeria marsh where they significantly reduced the regrowth of Puccinellia maritima.The main plant species ealen was Puccinellia maritima, especially in mid winter. Salicornia maritima agg. leaves and seeds formed much of the diet in autumn, whereas Triglochin maritima, Plantago maritima and Aster tripolium were important foods on Limonium/Armeria marsh in spring. All these species were selected at some part of the year. Selection was related to the proline (an imino acid used by salt‐marsh plants as an osmoregulator) and chloride content and avoidance related to tannins. Two species which contained condensed tannins. Limonium vulgare and Armeria maritima, were rarely eaten. As well as being a nutrient, proline may help to neutralize the effects of tannins in the diet if incorporated into proline‐rich proteins.

Vegetation Change on a Northeast Tidal Marsh: Interaction of Sea‐Level Rise and Marsh Accretion

Increasing rates of relative sea—level rise (RSL) have been linked to coastal wetland losses along the Gulf of Mexico and elsewhere. While such losses have yet to be reported for New England tidal marshes, rapidly rising RSL may still be affecting these systems. Studies of the Wequetequock—Pawcatuck tidal marshes over four decades have documented dramatic changes in vegetation that appear to be related primarily to differential rates of marsh accretion and sea—level rise. Other environmental factors such as sediment supply and anthropogenic modifications of the system may be involved as well. When initially studied in 1947—1948 the high marsh supported a Juncus gerardi—Spartina patens belting pattern typical of many New England salt marshes. On the most of the marsh complex the former Juncus belt has been replaced by forbs, primarily Triglochin maritima, while the former S. patens high marsh is now a complex of vegetation types–stunted Spartina alterniflora, Distichlis Spicata, forbs, and relic stands of S. patens. These changes are documented by vegetation sampling that closely followed the 1947—1948 methods and by peat core analysis. Marsh elevations were determined by leveling, and the mean surface elevation of areas where the vegetation has changed is significantly lower than that of areas still supporting the earlier pattern (4.6 vs. 13.9 cm above mean tide level). The differences in surface elevation reflect differences in accretion of marsh peat. Calculations based on sandy overwash layers deposited during historically recorded storms as well as on experimentally placed marker horizons of known age indicate that stable areas have been accreting at the rate of local sea—level rise, 2.0—2.5 mm/yr at least since 1938; changed areas have accreted at about one half that rate. Lower surface elevations result in greater frequency and duration of tidal flooding, and thus in increased peat saturation, salinity, and sulfide concentrations, and in decreased redox potential, as directly measured over the growing season at both changed and stable sites. It is proposed that these edaphic changes have combined to favor establishment of a wetter, more open vegetation type dominated by to distinctive communities–Stunted S. alterniflora and forbs. Changes documented on the Wequetequock—Pawcatuck system have been observed on the other Long Island Sound marshes and may serve as a model for the potential effects of seal—level rise on New England tidal salt marshes.

Spring staging in Brent Geese Branta bernicla: feeding constraints and the impact of diet on the accumulation of body reserves.

The diet composition of Brent Geese Branta bernicla on a salt-marsh was quantified. Puccinellia maritima was the principal food species, while Plantago maritima and Triglochin maritima were less commonly taken. Festuca rubra only acted as a substitute for Puccinellia when production of the latter species dropped. The metabolizable energy of the food plants ranged from 5 to 11 kJ·g-1. By assessing the ingestion rates of geese feeding on different food species, the net intake rate could be derived. Plantago and Triglochin appeared to be the most profitable plants to eat. The proportion of these species in the diet was restricted by (1) the capacity of the alimentary tract, since high intake rates combined with high water contents of the food plants easily led to overfill; and (2) the limited distribution of these plants, in combination with their rapid depletion by grazing geese. These latter factors led to an unequal allocation among individual geese. Most Plantago and Triglochin was obtained by dominant pairs within the flocks. The high quality of Puccinellia allowed geese to gain mass in spring, but the metabolizable energy of this plant species declined during the staging period, and Plantago and Triglochin increased in importance in supplying the geese with components with which to build their body reserves. The timing of the onset of spring growth of the various food species differed between years, and plant phenology was shown to have a profound effect on the final body reserves of the geese.

A survey of zinc, copper and cadmium concentrations in salt marsh plants along the Dutch coast

In autumn 1986, plants and soil were collected from the lower and the higher salt marsh zones of salt marshes along the Dutch coast. The main purpose was to get an overview of Zn, Cu and Cd concentrations in six dominant species of salt marsh plants. The roots and shoots of the plants were analysed for Zn, Cu and Cd. The highest heavy metal concentrations were found in plants collected from salt marshes near harbour areas and/or that are known to receive contaminated fluvial sediment. Dicotyledonous plant species tended to have similar heavy metal concentrations in roots and shoots, whereas in monocotyledonous species the concentrations in the roots were two to three times higher than in the shoots. Differences in accumulation in the roots between elements and between plant species were found. Cd was accumulated more than Zn or Cu. Triglochin maritima shows a low Cd uptake by roots, whereas Spartina anglica and Scirpus maritimus tend to accumulate it. The fraction of soil particles smaller than 63 μm, loss on ignition and Zn, Cu and Cd concentrations were determined in soil samples. The highest Zn, Cu and Cd concentrations in the soil were found at salt marshes in the Western Scheldt area and were nine, five and 20 times higher than background levels, respectively.

Growth, reproduction and resource allocation in halophytes

Different patterns of growth and reproduction in halophytes are examined in relation to their ability to colonise saline habitats. In many halophytes, vegetative propagules are produced which establish as “ready-made plants”, thereby bypassing the uncertainties of seedling establishment. In other species where agamospermy is well developed, genetic variation both within and between populations is limited. Halophytic species that have this type of breeding system are extremely salt tolerant and an individual has the potential to give rise to a population of genetically uniform plants which are adapted to a narrow ecological niche. However, in a number of halophytes both genetic variation between populations and phenotypic plasticity of individuals occur as “mixed strategies”, enabling them to cope with environmental heterogeneity. The value of integrating studies of genetic variation in populations with molecular, biochemical and ecological studies is evident, and such an integrated approach appears to be directly applicable to studies of salt tolerance in plant populations. Phenotypic plasticity in response to a changing environment is likely to be well developed in long-lived perennial halophytes. Conditions at the time of establishment may be very different from those one or two decades later. Leaf plasticity has been examined in plants of Triglochin maritima L. grown at different salinities. A reduction in both the number and size of leaves per shoot, and changes in the nutrient and water contents of leaves, occurred as the salinity increased. Acclimation to increased salinity took at least 50 days before the relative birth rate of leaves per shoot of plants in the different saline cultures was similar. The significance of the different types of asexual reproduction and the phenotypic adjustments are discussed in relation to resource availability for plant growth at high salinities.

Effects of metabolic inhibitors on Na+stimulated K+uptake in salicornia virginica roots: Possibility of metabolic coupling of the transport

Abstract Regarding the ionic interactions in the roots of the halophyte Salicornia virginica, it has been previously reported that high concentrations of NaCl stimulated the uptake of K+ in the presence of Ca2+, though the mechanism underlying this stimulating effect of Na+ remains largely unknown (Sopandie et al. 1990). The results obtained led us to examine the possibility of a metabolic linkage to this movement of K+ into the roots of Salicornia under saline conditions. Jefferies (1973) presented the evidence of the presence of an inward potassium pump operating in the roots of seedlings of Triglochin maritima treated with saline medium, when the concentration of potassium in the external solution was low.

Comparison of plant community–environment relations in two estuarine marshes of northern British Columbia

The Dala and Yakoun estuarine marshes in northern British Columbia were compared to evaluate similarities in species composition, plant communities, and vegetation–environment relationships. The Dala is a fjord-head marsh at the mouth of a glacially fed river with a fresh to brackish salinity regime and a 7-m tidal range. The Yakoun marsh is fed by lowland bog drainage on the Queen Charlotte Islands, has a salt to brackish salinity regime, and a 3-m tidal range. Both marshes contain similar dominant species (Carex lyngbyei, Deschampsia cespitosa, Potentilla pacifica, Triglochin maritimum), but share only about one third of the total (50) vascular species recorded. Four plant community types characterizing three main physiographic zones (low, intermediate, and high) were described at each marsh. Principal component analysis (PCA) of species composition data indicated similarities in general patterns of community organization at both marshes; however, PCA of soil chemical data indicated greater between-marsh differences, especially in intermediate and high zones. Canonical correlation analysis indicated that the Yakoun shows a closer connection between overall vegetation variation and substratum elevation, and a clearer elevational zonation of communities than the Dala. Examination of tidal regime data indicated that the Yakoun experiences steeper gradients in submergence time and flooding frequency than the Dala, thus offering an explanation for the different vegetation–elevation relationships.

An Ecophysiological Comparison of Measurements of the Diurnal Rhythm of the Leaf Elongation and Changes of the Leaf Thickness of Salt-resistant Dicotyledonae and Monocotyledonae

Rozema, J., Arp, W., van Diggelen, J., Kok, E. and Letschert, J. 1987. An ecophysiological comparison of measurements of the diurnal rhythm of the leaf elongation and changes of the leaf thickness of salt-resistant Dicotyledonae and Monocotyledonae.—J. exp. Bot. 38: 442–453. The continuous measurement of leaf elongation and leaf thickness with the use of a rotation potentiometer set up revealed a rapid and sensitive reaction of halophytic plants to conditions affecting the plant's water relations. At increased salinity (450 mol m–3 NaCl) the rate of leaf elongation decreased both in Aster tripolium and in Sparlina anghca. Increased shrinkage during the day and a long period for recovery swelling at night in leaves of Aster iripolium at increased salinity illustrates that water shortage is part of the cause of salinity-induced growth reduction. All dicotyledonous species analysed (Aster tripolium, A triplex hastata, A. littoralis, Suaeda maritima and Beta vulgaris) showed a day/night ratio of the leaf elongation rate lower than 1, while this ratio was higher than or equal to 1 in Monocotyledons (Spartina anglica, Juncus gerardii, J. maritimus, Festuca rubra ssp. litoralis, Elymus pycnanthus). With the exception of Triglochin maritima none of the monocotyledonous halophytes tested (Sparlina anglica, Juncus gerardii, J. maritimus, Festuca rubra ssp. litoralis, Elymus pycnanthus) exhibited a diurnal rhythm of leaf thickness changes, such as was observed for all dicotyledonous species studied (Aster tripolium, Atriplex hastata, A. littoralis, Salicornia brachyslachya, Suaeda maritima, Glaux maritima, Odontites verna ssp. serotina). The diurnal pattern of the leaf elongation rate and the leaf thickness changes can be explained by variation of photosynthetic rate and transpiration water losses by stomatal closure in the dark and opening in the light such as shown for the dicotyledon species Glaux maritima. This difference between dicot and monocot species in diurnal variation of the leaf elongation rate and leaf thickness may partly be explained in terms of the different position of the growth zone and possibly by a difference in elasticity of the tissue of halophytic monocotyledons and dicotyledons. The consequences of these differences are discussed.

OCCURRENCE AND ECOLOGICAL SIGNIFICANCE OF VESICULAR ARBUSCULAR MYCORRHIZA IN THE SALT MARSH ENVIRONMENT

SUMMARY The infection by vesicular arbuscular mycorrhizal fungi (VAM) of various salt marsh plant species has been estimated and compared. This kind of infection appeared to be high or intermediate and frequent in Aster tripolium, Plantago maritima, Glaux maritima and Festuca rubra ssp. litoralis, rare or absent in Spartina anglica, Triglochin maritima, Juncus gerardii, J. maritimus, A triplex hastata and Suaeda maritima and variable or intermediate in Salicornia dolichostachya and S. brachystachya. The sodium content of shoots of mycorrhizal Aster tripolium plants was lower than of nonmycorrhizal plants when grown at 300 mM NaCl. The potassium and phosphorus content of the shoot was not significantly affected by the presence of mycorrhiza. Improved growth of mycorrhizal plants of Aster tripolium under salinity stress could be related to increased leaf elongation and to smaller diurnal changes in the leaf thickness. Both parameters indicate increased water uptake by mycorrhizal roots. The causes of increased water uptake in mycorrhizal plants are discussed in terms of reduced root resistance to water transport and its consequences for prolonged stomatal opening and increased photosynthesis.