A comparative study of the tolerance of salt marsh plants to manganese

Summary Salicornia europaea, Puccinellia maritima, Triglochin maritima, Aster tripolium, Plantago maritima, Armeria maritima, Juncus gerardii andFestuca rubra, collected as seed from a salt marsh at Portaferry, County Down, were grown on saline (340 mM NaCl) and non saline nutrient solutions at five concentrations of manganese sulphate (0.025–10.0 mM). After an eight week growing period, shoot and root yields and the concentrations of sodium, potassium, calcium and manganese in the shoots were determined.Except forS. europaea the saline treatments had a strongly limiting effect on plant growth. Each of the species investigated showed a degree of tolerance to high concentrations of manganese which was similar to that of calcifuge species and plants characteristic of waterlogged sand dune slack communities, but which was very much greater than that ofArrhenatherum elatius a species usually excluded from acidic soils. There was little evidence to support the hypothesis that tolerance of high manganese concentrations was correlated with the position of the experimental plants in the salt marsh ecotone or that the manganese nutrition of halophytic and glycophytic marsh species differs. Whilst manganese uptake increased proportionally with solution manganese concentration, there were few other major effects of manganese on the balance of shoot cation concentrations in the plants investigated. Both antagonistic and synergistic effects of sodium on manganese uptake were recorded for different species.     

Aggregative responses of brent geese on salt marsh and their impact on plant community dynamics

The aggregative responses and habitat preferences of a generalist herbivore, the dark-bellied brent goose Branta bernicla bernicla, feeding on salt marshes are examined in relation to vegetation community characteristics and the abundances of individual plant species. In the autumn, feeding was strongly concentrated on the low marsh, which had the highest biomass of the preferred food plant, Salicornia europaea. There was a strong aggregative response of the geese to the abundance of S. europaea. A decline in the availability of S. europaea led to an increase in the pattern of aggregation in relation to the two other major food plants on the low marsh, Aster tripolium and Puccinellia maritima. The availability of these food plants, however, reached critically low levels in mid-winter and the geese abandoned the low marsh for the high marsh. Within the high marsh, the plant communities selected tended to be dominated by the inedible species Limonium vulgare. The food plants selected were P. maritima in the winter and P. maritima and Triglochinmaritimum in the spring. On the high marsh, aggregative responses were shown to both P. maritima and T. maritimum, but in both cases, aggregation increased up to a critical level of biomass, and then declined. The prevention of grazing with exclosures for 3 years led to an increase in the abundance of P. maritima on both high and low marshes. This change was slight on high marsh but pronounced on low marsh, where S. europaea showed a decrease in abundance in the exclosures over this time. The implications of the aggregative responses for the population dynamics of P. maritima and S. europaea are discussed. Received: 11 September 1997 / Accepted: 12 December 1997     

Impact of different sheep grazing intensities on salt marsh vegetation in northern Germany

Abstract. Mainland salt marshes in Schleswig-Holstein (northern Germany) have been grazed intensively by sheep for several decades. In 1988 experimental sites were established in the lower and middle salt marsh of Sönke-Nissen-Koog and subjected to different grazing intensities. From 1989 to 1993 the impact of sheep grazing on the composition and structure of the salt marsh vegetation was studied through the yearly analysis of permanent plots, vegetation mapping and measurements of the vegetation height. The intensively grazed site (10 sheep/ha) is covered by a short monotonous Puccinellia maritima sward with Salicornia europaea and Suaeda maritima. Halimione portulacoides and Aster tripolium, especially flowering plants, are rare. On the sites with 1.5 and 3 sheep/ha Puccinellia maritima remained dominant. The population density of Salicornia europaea decreases after reduction of the grazing intensity, whereas Suaeda maritima finds optimal growing conditions. Stands of Halimione portulacoides and flowering Aster tripolium plants are rare near the sea dike but their cover and size increases further away from the dike. In the plot with 1.5 sheep/ha the height of the vegetation increases along the gradient from the dike towards the tidal flats, due to local differences in actual grazing intensity. When grazing is stopped, Puccinellia maritima is successively replaced by Festuca rubra, Halimione portulacoides and Aster tripolium. High variability of vegetation height indicates structural diversity. Patches of higher and lower vegetation correspond with the distribution pattern of different plant species. In terms of nature conservation cessation of grazing is recommended.     

Directional and non‐directional vegetation changes in a temperate salt marsh in relation to biotic and abiotic factors

Abstract. The effects of reduction and cessation of sheep grazing on salt‐marsh vegetation were studied on a formerly intensively grazed salt marsh in northern Germany. Plant species cover was recorded in 45 permanent plots from 1992 to 2000. In 1995, physical and chemical soil parameters were analysed. Results of Redundancy Analysis (RDA) indicated that salinity and the depth of anoxic conditions below the surface were the most important soil factors related to the spatial vegetation pattern. Furthermore, plant species distribution was influenced by present and past grazing intensity, by soil grain size and nitrogen content. Vegetation changes over 9 yr were analysed by non‐linear regression. The cover of Aster tripolium, Atriplex portulacoides, and, to a lesser extent, Artemisia maritima and Elymus athericus increased due to reduced grazing pressure, whereas the cover of Salicornia europaea decreased. After a strong increase in the first years Aster decreased 2 to 6 yr after abandonment. In the mid salt‐marsh zone Puccinellia maritima was replaced by Festuca rubra. The cover of Puccinellia, Festuca, Suaeda maritima, Glaux maritima and Salicornia fluctuated strongly, probably due to differences in weather conditions and inundation frequency. Species richness per 4 m² generally increased while vegetation evenness decreased during the study period. Only in the high salt marsh abandoned for 9 yr did the number of species decrease slightly. Thus far, cessation of grazing did not lead to large‐scale dominance of single plant species.     

Long-term changes (1953–1990) in the salt marsh vegetation at the Boschplaat on Terschelling in relation to sedimentation and flooding

Long-term vegetation changes in permanent plots along two transects from the low to the high salt marsh at the Boschplaat on Terschelling between 1953 and 1990, were analysed in relation to sedimentation and flooding. In both transects, the number of plant species decreased between 1953 and 1990. In lower parts of the two transects the dominant plant species of the vegetation changed from Puccinellia maritima in 1953/54 to Limonium vulgare in 1980 to Atriplex portulacoides in 1990. The increase in A. portulacoides between 1980 and 1990 coincided with an increase in the thickness of the silt layer, caused by a sedimentation rate of about 5 mm per year. This sedimentation led to an increase in elevation but not to large changes in flooding frequency between 1953 and 1990, probably due to a sea level rise during the same period.In the higher parts of the salt-marsh transects Elymus athericus strongly increased and this species became dominant in 1980 and 1990. In these parts of the salt marsh, a small increase in elevation, in thickness of the silt layer, and in flooding frequency occurred between 1953 and 1990.The described changes in vegetation are discussed in terms of general succession of salt-marsh vegetation in relation to flooding and sedimentation.     

AN ECOPHYSIOLOGICAL STUDY OF THE SALT SECRETION OF FOUR HALOPHYTES

Plants of Spartina anglica, Limonium vulgare, Armeria maritima and Glaux maritima were collected in the field and grown on different concentrations of NaCl, KCl and CaCl₂. Salt secretion, ion content, water content and transpiration rates were determined. The highest sodium secretion was found in Spartina anglica , a species from the most saline habitat; and a somewhat lower secretion rate in Limonium vulgare. The lowest rates were found in Glaux maritima and Armeria maritima. The sodium secretion efficiency, i.e. the ability to maintain an unchanged internal sodium content, was highest in Spartina anglica. Spartina anglica is the most successful in the removal of excessively absorbed salt, since it secretes 60% of the absorbed sodium. The values for Limonium vulgare, Glaux maritima and Armeria maritima were 33, 20 and 4% respectively. The species studied differ in the preferential sequence of ion secretion as well as in secretion rate and efficiency. This preferential sequence of ion secretion seems to be similar in members of the same taxonomic group (Plumbaginaceae). The comparability of the secretion parameters is discussed with regard to morphological differences between the species.     

The effect of cattle and sheep grazing on salt-marsh vegetation at Skallingen,Denmark

The aggregated effect of cattle and sheep grazing on Puccinellion maritimae and other salt-marsh vegetation has been studied together with changes in species composition, the percentage cover of each species, total cover and the percentage of bare ground, six years after grazing had been prevented by construction of experimental exclosures. The results of these experiments are discussed in relation to the natural development of the vegetation that occurred in a permanent plot in the ungrazed part of the salt marsh. Six years without grazing caused a marked increase in total cover and a dramatic reduction in the amount of bare ground. The species composition of the Puccinellia maritima community did not change during these six years, but all species increased in cover. Whereas Artemisia maritima migrated into the Festuca rubra community and only two species Festuca and Halimione portulacoides, increased in cover, all other species showed reduced cover and Salicornia europaea disappeared from the plot after six years without grazing. During the same period of time, three species, Salicornia europaea, Suaeda maritima, and Glaux maritima, disappeared from the plot in the ungrazed marsh as a result of natural development. During thirty-five years the vegetation originally dominated by Puccinellia maritima and Salicornia europaea has changed into a community dominated by Halimione portulacoides, whereas the grazed salt marsh is still dominated by Puccinellia maritima and Salicornia europaea. These results are discussed in relation to the literature on the effect of cattle and sheep grazing on salt-marsh vegetation.     

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

Summary 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.     

Effects of temperature,salinity and cold stratification on seed germination in halophytes

Salt tolerance of halophytes corresponds with the habitat requirement of the species. It is an important factor during the germination phase and it can determine successful establishment. This paper presents the effects of alternating temperature–light regimes (4/8°C, 10/20°C, 20/32°C; 12 h dark: 12 h light) and different salinity levels (0, 200, 400, 600 mmol l²¹ NaCl) on seed germination of five halophytes, Halimione pedunculata, Bupleurum tenuissimum, Aster tripolium, Triglochin maritimum and Armeria maritima. The five species differ with respect to family and life‐form and spatially correspond to a decreasing salt gradient (i.e. distance from salt water, with H. pedunculata being the most tolerant and A. maritima being the least). Armeria maritima, A. tripolium and T. maritimum seeds were additionally subjected to a cold stratification experiment. The results showed that Halimione pedunculata, an annual therophyte of year‐round heavily saline habitats, was dormant under all experimental conditions. Bupleurum tenuissimum, a species typical to sites of varying salinity prone to leaching during spring and autumn rainfall, germinated best under cold and warm temperatures, but only under non‐saline conditions. Aster tripolium and T. maritimum, close neighbours in salt marshes, showed very similar germination behaviour: seeds of both species tolerated high levels of salinity and germinated best in summer temperatures during periods of highest soil salinity, and germination was significantly promoted by cold. Armeria maritima, a species usually found on the marginal fringes of saline habitats, germinated only under low salt levels and maximum germination was under cold (spring) and warm (autumn) temperatures, with no significant effect of cold stratification.     

Diet and habitat use of moulting Greylag Geese Anser anser on the Danish island of Saltholm

The diet and habitat use of moulting Greylag Geese Anser anser were studied at the recently established moulting site on the island of Saltholm, between Denmark and Sweden. Classification of the vegetation in the area most used by Greylag Geese during their moult showed that the geese selected low saltmarsh habitats which were richest in Common Saltmarsh- grass Puccinellia maritima and that dropping density was highly correlated with Puccinellia cover. Geese showed slowest step rates and highest peck rates in vegetation types rich in Puccinellia. Examination of faecal material confirmed that the geese fed almost exclusively on PuccineEia during the main moult period, despite its limited spatial distribution. Puccinellia maritima exhibited the highest levels of protein of any of the graminoid species present except for the belowground lower stem base of Sea Club-rush Scirpus maritimus, which offers a nongrowing food resource which is difficult to extract and consume. The results of this study suggest that the statement that the "limited data available for moulting waterfowl indicate no active selection for proteinaceous foods; i.e., birds are selecting foods in proportion to their availability" does not hold for Greylag Geese moulting on Saltholm.     

Ecological consequences of tidal management for the salt-marsh vegetation

Presently a storm-surge barrier is under construction in the mouth of the Oosterschelde. After its completion tidal conditions in the estuary can be controlled. In order to indicate the limiting conditions for conceivable uses of the storm-surge barrier a number of the most prominent salt-marsh species were tested in their various life stages against immersion times of 2, 4 and 8 days.Most of the species were able to withstand an extended immersion fairly well, although some of them showed reduced growth during-and after immersion. No evident relation was found between the position of the species on the salt-marsh ecotone and their inundation tolerance. Only one taxon from the upper marsh, Festuca rubra ssp. litoralis, showed a total die-back after an 8 day summer inundation. Most of the species involved showed a decreasing immersion tolerance with increasing water temperatures. Limonium vulgare and Juncus gerardii, however, exhibited a significant growth increase after extended immersion, even at a temperature of the inundation water of 36°C.In contrast herewith flowers and flower buds started to decay after as little as a 2 day immersion. For Aster tripolium prolonged immersion reduced seed weight and germination capacity of the seeds. Germination and seed weight of Salicornia dolichostachya were not affected by prolonged immersion.It is concluded that prolonged summer inundations will cause an overall negative effect on the salt-marsh vegetation.Nomenclature follows Tutin et al., (1964–1980).Communication nr 295 of the Delta Institute for Hydrobiological ResearchThanks are due to Mrs. M. A. Vink, Miss M. Bouts and Miss H. Geltink for their assistance. The study was funded by the Ministry of Transport and Public Works, Rijkswaterstaat Delta Department, Environmental Division (project VEGIN).     

Are spring staging brent geese evicted by vegetation succession?

The number of spring staging brent geese on the salt marshes of the Dutch island of Schiermonnikoog increased from about 1500 individuals in the late 1960s to > 4000 in the late 1970s. Since then, numbers on Schiermonnikoog have levelled off, while the world population continued to increase. Although the extent of salt-marsh area on the island has dramatically increased over the past 20 yr, the number of brent geese on Schiermonnikoog was rather constant in this period. We hypothesise that the number of geese did not increase because of successional changes in the vegetation.
On the basis of 24 yr of counts, we show that geese had to give up older parts of the marsh. Over time, tall growing species like the shrub Atriplex portulacoides have invaded, making the marsh unsuitable for goose grazing. Newly developed marsh, however, was readily exploited by the geese. The area of older salt marsh lost due to succession was almost exactly compensated for by the development of new feeding grounds. Geese which persistently utilised the older marsh were faced with a high proportion of non-preferred species, although they still managed to assemble a diet largely composed of preferred plant species. In the older marsh, a significant reduction in the time spent foraging was also observed. We conclude that brent geese are largely excluded as vegetation succession progresses. Numbers on the island as a whole, however, are sustained due to the dynamic nature of the island. If development of new salt marshes were to be prevented, geese would be forced to abandon the salt marsh.     

EVALUATION OF PROLINE ACCUMULATION IN THE ADAPTATION OF DIVERSE SPECIES OF MARSH HALOPHYTES TO THE SALINE ENVIRONMENT

Proline accumulation by eight major species of salt marsh halophytes was examined under growth chamber and field conditions. When the plants were exposed to increasing salinities in the growth chamber, they accumulated proline after a threshold salinity had been reached. Three general patterns were apparent. Limonium carolinianum (Walt.) Britt. and Junius roemerianus Scheele began to accumulate proline at 0.25 m NaCl with accumulations up to 63.6 μmoles per gram fresh weight at higher salinities. The C₄ grasses, Spartina alterniflora Loisel., Spartina patens (Aiton) Muhl., and Distichlis spicata (L.) Greene, had threshold salinity levels around 0.5 m NaCl and accumulated proline to 27.4 μmoles per gram fresh weight. The succulents, Salicornia bigelovii Torr., Salicornia virginica L., and Borrichia frutescens (L.) DC, did not accumulate proline until very high salinities (0.7 m) were reached. Water stress imposed by polyethylene glycol instead of NaCl caused similar proline accumulation in the species studied, but to different extents. Field measurements of proline content and soil salinities correlated well with the findings from growth chamber experiments. Rates of proline accumulation and breakdown in L. carolinianum were sufficient for osmotic adjustment by the plant to the changes in interstitial salinity in the marsh. The significance of proline accumulation as an adaptation to the salt marsh environment was species specific. We suggest that proline accumulation is of considerable importance in L. carolinianum and J. roemerianus, important to the C₄ grasses at certain times and in certain locations in the marsh, and of little importance in the succulents.     

A Study on Polymorphism in Aster tripolium L. (Sea Aster)

Abstract: Genotypic and environmental variation in Aster tripolium L. was studied in common garden experiments and in transplantation experiments in different saltmarsh sites along the estuarine gradient of the Westerschelde and along the elevation gradient of individual saltmarshes. Analysis of the variation in a number of morphologic characters of the inflorescences indicated that this variation is both environmentally as well as genetically controlled. Morphologic differences between an Aster tripolium population of a brackish marsh and a number of populations of a saline marsh were unchanged whether the plants were growing in their original habitat or in a transplant habitat. The population from the brackish marsh had smaller inflorescences with ray florets and a predominantly biennial life cycle, in contrast with the populations of the saline marsh, which had larger inflorescences usually without or with a few ray florets and showed a tendency to a perennial life cycle. We concluded that the variation between the populations of the saline and the brackish marsh is mainly genetically controlled, while the variation within the saline marsh is mainly environmentally controlled.     

Sulphide tolerance in coastal halophytes

The effect of sulphide on the growth of several species of salt-marsh plants was investigated. Relative growth rates were significantly reduced in two upper-marsh species, Festuca rubra and Atriplex patula, and in the lower-marsh species Puccinellia maritima. However the growth of Salicornia europaea, a species frequently associated with sulphide-containing sediments, was unaffected. In a separate experiment the wide ranging halophyte Aster tripolium, also appeared to be tolerant of sulphide at a concentration frequently encountered in salt marshes. Sulphide pretreatment inhibited the activity of two metallo-enzymes, polyphenol oxidase and external phosphatase, in plants from the upper marsh, but had no effect on enzymes from P. maritima or S. europaea. The rate of respiration by root tissue was significantly reduced in all of the species investigated but whereas the uptake of ⁸⁶rubidium was markedly inhibited in the other three species, uptake by S. europaea showed a significant stimulation. Similarly, whereas sulphide-grown plants of F. rubra, A. patula and P. maritima had a considerably reduced tissue iron content, the total iron concentration in S. europaea tissues was comparable to that of the controls. When the sulphide-tolerant species A. tripolium was grown in sulphide-containing media there was no significant effect on the tissue concentration of any of the elements investigated. These results are discussed in relation to possible mechanisms of sulphide toxicity and resistance.     

Habitat switching by dark-bellied brent geese Branta b. bernicla (L.) in relation to food depletion

Seasonal changes in the distribution and feeding behaviour of dark-bellied brent geese Branta b. bernicla (L.) and the biomass of their food plants were studied in three successive winters on the Norfolk coast. The data was used, in conjunction with published information, to show how depletion, productivity and mortality of food plants drive the pattern of habitat switching in this species. It is then possible to explain the habitat shifts observed over the last 35 years and predict future changes. On arrival, geese fed first on algal beds and then on salt marsh, grass and arable fields before returning to feed entirely on the salt marsh in spring. The biomass of green algae, and subsequently the salt marsh vegetation, declined during the autumn and this could be attributed to depletion through goose grazing and natural mortality. As depletion occurred the geese fed more intensively, for a greater percentage of time and with an increasing pace rate, the net result, however, was a declining intake rate (as measured by defaecation rate). The algal biomass at which the geese switched from the algal beds to salt marsh was consistent between years, with heavy storm-induced loss of algae in one year resulting in an earlier switch. That the timing of habitat switches may be explained by depletion of food plants was further supported by historical data: the number of brent geese wintering at the site has increased dramatically over the last 30–35 years and the time of switching from algal beds to salt marsh and from salt marsh to salt marsh and fields has become progressively earlier, as expected from the increased depletion. The expected further increase in brent goose numbers will increase the rate of depletion of intertidal vegetation so that the switches between habitats will be more rapid and the geese will move inland earlier and remain inland longer. The expected increase in the brent goose population will thus result in a disproportionate increase in the levels of conflict between brent geese and agriculture.     

Repeated grazing of a salt marsh grass by moulting greylag geese Anser anser– does sequential harvesting optimise biomass or protein gain?

The effects of simulated goose grazing on common saltmarsh-grass Puccinellia maritima plants were tested on a Danish salt marsh during the flightless moulting period of greylag geese Anser anser (3–21 June 1998). Plants in an area exclosed from the influence of grazing and the nutrient effects of goose faeces were subject to removal of youngest lamina at 3-, 6-, 9- and 18-day intervals during this period. Average biomass and protein accumulation between harvests was highest at defoliation intervals of 9 days or more. Field observations from two separate study areas demonstrated geese returned to regraze the Puccinellia sward after 6–8 days and oesophageal contents from feeding geese showed selection for lamina lengths consistent with the results of clipping every 6 days. Geese therefore regrazed Puccinellia patches at shorter intervals than expected were they to maximise their intake of biomass or protein at each visit. However, total cumulative lamina elongation, equivalent to the long term gain during the entire moult period, showed no significant difference between the three most intensive defoliation treatments, which were significantly greater than those of plants defoliated at 18 day intervals. Highest overall lamina protein levels were maintained at 6- and 9-day defoliation intervals. This suggests geese regrazed Puccinellia patches at a rate that maximised their number of harvests during the flightless period, but maintained highest protein levels and overall biomass in the sward. This suggests, in line with earlier studies, that moulting greylag geese combine dietary selection, reduced nitrogen excretion and regrazing patterns to meet protein demands during regrowth of flight feathers.     

Low-molecular-weight carbohydrates in some salt-stressed plants

A study was made of the effects of salinity on the concentrations of free sugars, glycinebetaine, proline and other chemical components of Aster tripolium L., Daucus carota L., Honkenya peploides (L.) Ehr. and Plantago coronopus L. (Dicotyledones); and Carex extensa Good., Eleocharis uniglumis (Link) Schutt., Juncus maritima Lam. and Schoenoplectus tabernaemontani (C. C. Gmel.) Palla (Monocotyledones) grown in the laboratory. In Plantago coronopus the level of the polyol sorbitol increased when the plants were subjected to NaCl stress, while in Honkenya peploides the cyclitol pinitol accumulated. No consistent pattern emerged with respect to the changes in free sugar contents in either the monocotyledonous or dicotyledonous plants, though the monocotyledonous plants generally had higher sugar contents.     

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 thediurnal rhythm of the leaf elongation and changes of the leafthickness of salt-resistant Dicotyledonae and Monocotyledonae.—J.exp. Bot. 38: 442–453. The continuous measurement of leaf elongation and leaf thicknesswith the use of a rotation potentiometer set up revealed a rapidand sensitive reaction of halophytic plants to conditions affectingthe plant's water relations. At increased salinity (450 molm^–3 NaCl) the rate of leaf elongation decreased both inAster tripolium and in Sparlina anghca. Increased shrinkageduring the day and a long period for recovery swelling at nightin leaves of Aster iripolium at increased salinity illustratesthat water shortage is part of the cause of salinity-inducedgrowth reduction. All dicotyledonous species analysed (Aster tripolium, A triplexhastata, A. littoralis, Suaeda maritima and Beta vulgaris) showeda 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 rubrassp. litoralis, Elymus pycnanthus). With the exception of Triglochinmaritima none of the monocotyledonous halophytes tested (Sparlinaanglica, Juncus gerardii, J. maritimus, Festuca rubra ssp. litoralis,Elymus pycnanthus) exhibited a diurnal rhythm of leaf thicknesschanges, such as was observed for all dicotyledonous speciesstudied (Aster tripolium, Atriplex hastata, A. littoralis, Salicorniabrachyslachya, Suaeda maritima, Glaux maritima, Odontites vernassp. serotina). The diurnal pattern of the leaf elongation rateand the leaf thickness changes can be explained by variationof photosynthetic rate and transpiration water losses by stomatalclosure in the dark and opening in the light such as shown forthe dicotyledon species Glaux maritima. This difference betweendicot and monocot species in diurnal variation of the leaf elongationrate and leaf thickness may partly be explained in terms ofthe different position of the growth zone and possibly by adifference in elasticity of the tissue of halophytic monocotyledonsand dicotyledons. The consequences of these differences arediscussed. Key words: Leaf elongation rate, leaf thickness, water relations, salt resistance, Dicotyledonae, Monocotyledonae     

The arbuscular mycorrhizal fungus Glomus geosporum in European saline,sodic and gypsum soils

Plants of saline and sodic soils of the Hungarian steppe and of gypsum rock in the German Harz mountains, thus soils of high ionic strength and electric conductivity, were examined for their colonization by arbuscular mycorrhizal fungi (AMF). Roots of several plants of the saline and sodic soils such as Artemisia maritima, Aster tripolium or Plantago maritima are strongly colonized and show typical AMF structures (arbuscules, vesicles) whereas others like the members of the Chenopodiaceae, Salicornia europaea, Suaeda maritima or Camphorosma annua, are not. The vegetation of the gypsum rock is totally different, but several plants are also strongly colonized there. The number of spores in samples from the saline and sodic soils examined is rather variable, but high on average, although with an apparent low species diversity. Spore numbers in the soil adjacent to the roots of plants often, but not always, correlate with the degree of AMF colonization of the plants. As in German salt marshes [Hildebrandt et al. (2001)], the dominant AMF in the Hungarian saline and sodic soils is Glomus geosporum. All these isolates provided nearly identical restriction fragment length polymorphism (RFLP) patterns of the internal transcribed spacer (ITS) region of spore DNA amplified by polymerase chain reaction (PCR). Cloning and sequencing of several PCR products of the ITS regions indicated that ecotypes of the G. geosporum/ Glomus caledonium clade might exist at the different habitats. A phylogenetic dendrogram constructed from the ITS or 5.8S rDNA sequences was nearly identical to the one published for 18S rDNA data (Schwarzott et al. 2001). It is tempting to speculate that specific ecotypes may be particularly adapted to the peculiar saline or sodic conditions in such soils. They could have an enormous potential in conferring salt resistance to plants.