Menyanthes Research Articles

Nutrient dynamics in a floating mat and pond system with special reference to its vegetation

AbstractChemical properties of waters and their seasonal changes were studied in Mizorogaike Pond, a system of pond and floating mat. The following six sites including contrasting habitats and water conditions were monitored to assess nutrient dynamics in the system: 1) a pool on the mat, 2) margin of a Sphagnum cuspidatum community, 3) an artificial ‘well’ (water layer beneath the floating mat), 4) a Menyanthes trifoliata community in a hollow, and 5) & 6) two sites in the open water. On the floating mat, the water around the Sphagnum community had lower pH values, while that in the M. trifoliata community had higher pH values. This difference was related to the influence of flood water, the extent of which was determined by the microtopography. Seasonal changes in water chemistry on the mat suggested that pond water flooding the mat in late autumn and winter is important for the nutrient supply to the mat surface vegetation in this system. Water chemistry of the ‘well’ suggested that the diffusion of inorganic nitrogen occurs from beneath the peat layer. Two types of cluster analysis based on the mean values for chemical variables and the patterns of fluctuation in these variables were performed. The six sites were classified into similar groups which were identified by water type (pool, hollow, well and open water) by both types of analysis. The results showed that a common kind of perturbation should operate in determining the status of nutrient dynamics in the various water types.

日本海西部沿岸地域の更新世中期以降の植生変化

In the eastern and middle San-in districts, on the southern coast of the Western Japan Sea, the following floral change is recognized since the middle Pleistocene.There were three types of flora during the middle Pleistocene. First was the interglacial flora composed of cool temperate forest elements such as Fagus crenata, Quercus sp., Cryptomeria japonica, etc., and a pollen assemblage which is predominated by Fagus or represented by Fagus and Cyptomeria. Second is the glacial flora composed of subarctic elements as Picea jezoensis, Tsuga diversifolia, Menyanthes trifoliata, etc., and pollen assemblage represented by Pinus Subgen Haploxylon and Picea. Third is the interstadial flora composed of pollen assemblages represented by Picea and Cyptomeria.During the late Pleistocene, a fourth type of flora appeared, composed of warm temperate forest elements with pollen assemblages containing Cyclobalanopsis. Moreover, some species occur in each type of flora: Pinus koraiensis occurs in glacial flora, Lagerstroemia pollen in interglacial and Buxus microphylla var. japonica and Pseudotsuga japonica in interstadial. By means of pollen analysis, the latest Pleistocene and Holocene pollen zones are clearly identified as follows.Quercus and Alnus PZ: before about 10, 000y.B.P.Quercus and Aphananthe-Celtic PZ: about 10, 000 to 9, 000y.B.P.Fagus and Tsuga PZ: about 9, 000 to 7, 000y.B.P.Pinus and Abies PZ: about 7, 000 to 5, 500y.B.P.Cyclobalanopsis and Castanopsis PZ: about 5, 500 to 2, 400y.B.P.Gramineae PZ: about 2, 400y.B.P. to presentCryptomeria Subzone: about 2, 400y.B.P. to about A. D. 700Typical Subzone: about A. D. 700 to 1, 500Pinus Subzone: about A. D. 1, 500 to later than 1, 900Pinus and Cyptomeria Subzone: later than A. D. 1, 900 to present.

The paleoecology of a peatland complex in continental western Canada

The development of the present day vegetation, water chemistry, and landform features of a peatland complex in northeastern Alberta, Canada, was studied through analyses of macrofossils, peat stratigraphy, and inferred profiles. The Mariana Lakes peatland (55°54′N, 112°04′W) contains two geographical areas and four landform features (open lake basin, closed lake basin, water tracks, and forested Sphagnum islands). The surface vegetation was classified using TWINSPAN into four vegetation groups: (i) shrubby, open forest of Salix pedicellaris and Carex paupercula, (ii) closed Picea mariana forest, (iii) Sphagnum lawns of Sphagnum fallax, and (iv) Sphagnum carpets of Sphagnum subsecundum and Menyanthes trifoliata. Within the peatland complex, surface water chemistry ranges from a pH of 3.6 to 6.3, reduced conductivity of 0 to 232 μS, calcium content of 1.1–15.6 mg/L, and magnesium content of 0.6–2.8 mg/L. Peat macrofossils analyzed quantitatively were arranged (by TWINSPAN) into six macrofossil assemblages and were correlated to peat calcium content. Inferred pH profiles derived from linear regression transformations, and inferred-moisture profiles derived from a weighted moisture index, describe natural acidification and water levels. The mean initial inferred pH was at 5.6 ± 0.2, and mean initial inferred moisture indexed at 3.1 ± 0.2. Mean present day inferred pH is 4.9 ± 0.7, and mean moisture is 2.8 ± 0.6. Organic deposition at Mariana Lakes began about 8200 years BP in the closed lake basin. Filling-in of the lake basin produced a floating mat that upon enclosure developed into a poor fen. Paludification of the upper fen began about 6000 years BP, subsequent to terrestrialization in the lake basin, and progressed in a downslope direction. By 2960 years ago the entire drainage path was paludified.

The vegatation, surface water chemistry and peat chemistry of moderate-rich fens in central Alberta, Canada

The non-forested fens of the Athabasca area in central Alberta, Canada are characterized by their surface water and peat chemistry. Correlations between vegetation and chemical gradients are examined. The primary vegetation gradient is from stands dominated byDrepanocladus vernicosus, Meesiatriquetra, Menyanthes trifoliata, andCarex chordorrhiza to those dominated byBrachythecium mildeanum, Drepanocladus aduncus, Carex aquatilis, andDrepanocladus polycarpus. This vegetation gradient reflects a chemical gradient of increasing pH, magnesium, sodium, sulphur, organic nitrogen, and phosphorus in the fen water and increasing magnesium, iron, and phosphorus in the fen peats. Potassium and sodium in the fen peats show a decreasing trend along the vegetation gradient. A second gradient from shrub-moss vegetation to sedge-moss vegetation is significantly correlated with microtopography and an increase in nitrate content in the spring (May) waters. The fen waters in this study are in the 5.3–7.1 pH range, with specific conductance of 18–240μS. The calcium contents of the waters averages 19.5–22.1 mg/l and that of magnesium averages 4.3–5.3 mg/l in spring and fall, respectively. The subsurface fen peats are characterized by mean calcium contents of 17,426 mg/kg and magnesium contents of 1,719 mg/kg. Organic nitrogen, nitrate, and ammonium content in the spring and fall waters average 1,967–2,395 μg/l, 3.1–9.8 μg/l, and 16.8–88.9 μg/l, respectively.

Heterostyly and gene-flow in Menyanthes trifoliata L. (Menyanthaceae)

NIC LUGHADHA, E. M. & PARNELL, J. A. N., 1989. Heterostyly and gene-flow in Menyanthes trifoliata L. (Menyanthaceae).Menyanthes trifoliata is shown to be a self-incompatible heterostylous species with a suite of associated pollen and gynoecium dimorphisms. These features may promote legitimate pollination. Analysis of a natural population showed substantial pollen inviability, a preponderance of illegitimate pollen on stigmas and a possible asymmetry of pollen flow. Mean pollen travel was estimated as 2.6 m by counting legitimate grains on stigmas whose distance from the nearest source of legitimate pollen was known. Direct field and laboratory measurement indicated mean seed travel of <0.2m. The density of flowering spikes varied greatly within the studied colony of Menyanthes, with a mean of 0.93 m-2. Using suitable corrections the genetically effective density was estimated as between 0.04 and 4.4 m-2. Crossing experiments indicated that Menyanthes is fully outcrossed (r=1). The neighbourhood area was estimated as 10–15 m2 while neighbourhood size ranged from less than one to sixty-five. Some published neighbourhood estimates are revised with the results for Menyanthes being at the lower end of the range. If the genetically effective density were estimated more accurately, neighbourhood estimates would likely be lower still. It is concluded that what is generally referred to as a population of Menyanthes, may actually represent many evolutionary units.

Plant Production, Decomposition, and Carbon Efflux in a Subarctic Patterned Fen

Measurements of plant biomass and primary productivity, plant-tissue decomposition, and gas flux were made at sites representing strings, flarks, and pools in a strongly patterned fen near Schefferville, northern Quebec. Biomass and production were strongly related to the position of the water table, with biomass ranging from an average of 190 g m-2 on the strings to 7 g m-2 in the pools. Scirpus cespitosus shoots and Chamaedaphne calyculata leaves decomposed slowly at both string and pool sites, losing 25 to 35% of their mass after 3 yr. In contrast, Menyanthes trifoliata, characteristic of the deeper pools, lost 80%7 of its mass after 3 yr. Carbon dioxide dominated the gas flux at the string site, but there were significant fluxes of methane at the flark and pool sites (7-8 g m-2 yr-'). A carbon budget, based on production and gas flux, suggested that the string site gained carbon at about 40 g m-2 yr-', whereas the flark site (with the water surface very close to the peat surface) lost about 15 g m-2 yr-' and the pool site (with the water surface about 25 cm above the peat surface) showed a very small loss (about 2 g m-2 yr-'). The results show that differential rates of plant production, combined with differences in the rates of plant tissue decomposition and methane efflux, contribute to the expansion of the flark/pool morphology at the present time.

Weitere Untersuchungen zur Verteilung und Struktur der Bitterstoffe vonMenyanthes trifoliata

Comparison of the methanolic extracts from leaves, stems, and rhizomes of MENYANTHES TRIFOLIATA L. by TLC showed that the main compounds are dihydrofoliamenthin, menthiafolin, and loganin, whereas foliamenthin was lacking. The monoterpene carboxylic acid of dihydrofoliamenthin was determined to be a derivative of nerol and the configuration of carbon 7 of the secoiridoid skeleton was shown to be beta by spectroscopic evidences.

Variation in tissue element concentration in mire plants over a range of sites

Elements in surface peat and ground water were estimated on seven mire sites in central and north Sweden. The variation in tissue clement concentration was studied in eleven plants occurring on the studied sites. The elements estimated were: N, P, K. Ca, Mg, Fe, Mn, Zn, Al, Cu, Mo, Na, S, B, and Si. The species studied were; Carex diandra, Carex limosa, Carex rostrata, Epilobium palustre, Menyanthes trifoliate, Pedicularis palustris, Rumex acetosa, Saxifraga hirculus, Scirpus hudsonianus, Stellaria crassifolia and Tofteldia pusilla. In surface peat over the range of sites, the variation in total concentrations of nitrogen and phosphorus was six and tenfold, respectively. The variation in total concentration of potassium was four‐fold. Extractable concentrations of these three elements showed an even greater variation between sites. Over the range of sites, the variation in tissue element concentration was larger in roots than in above‐ground parls. In above‐ground parts, floral parts varied less in tissue element concentration than did stems and leaves. The largest variation in tissue element concentration was found in Carex rostrata and Menyanthes trifoliata. The smallest variation was found in Saxifraga hirculus. Tissues of the rich fen species Saxifraga hirculus and Stellaria crassifolia had the lowest concentrations of heavy metals. The correlation between substrate element concentration and tissue concentration differed both between tissues and species. Concentrations of N, P and K in tissues of the Carex species were highly correlated with the concentrations of these elements in the substrate, while N, P and K concentrations in tissues of the herbaceous species, especially Saxifraga hirculus. correlated less well.

Heterostyly, homostyly, and long-distance dispersal of Menyanthes trifoliata to Greenland

An old report of homostyly in Menyanthes trifoliata L. in Greenland has been used as supporting evidence for the generally accepted hypothesis called Baker's law of long-distance dispersal. Measurements of flowers from both Denmark and Greenland throw considerable doubt on the existence of homostyly in this species. Several reports and observations suggest that seeds of M. trifoliata are frequently brought to Greenland by a few species of birds, especially geese, and that its seeds have great buoyancy in water.

Content of Phenolic Acids in Leaves of Menyanthes trifoliata

Content of Phenolic Acids in Leaves of Menyanthes trifoliata

Chemical composition of the reindeer summer and winter food

Semi-domesticated reindeer eat dur ing the per iod of snow cover main ly l ichen (Cladina spp.), w h i c h they must dig for in the snow. In the southern part of the F inn i sh reindeer herding area reindeer can also eat arboreal lichens (Alectoria and Bryoria spp.) and frozen Descbampsia flexuosa hay. D u r i n g summer reindeer feed on over 350 species of various plants, mainly sedges (Carex spp.), cottonsedges (Eriopborum spp.), shrubs, numerous grass and herb species and leaves f rom trees. The chemical compos i t ion of reindeer food was studied dur ing summer 1983 in 88 sampling areas in the reindeer herding area of F in land . The nutri t ive value of g rowing tundra plants, sedges and grasses is very high and reindeer always select the highest quali ty forage available. The reindeer's summer food contains usually about 2 2 % crude fibre and 15% crude protein i n D M . The crude prote in content varied in different areas and was 7.1 to 16.3% of D M in D. flexuosa, 8.5 to 18 .2% in Equisetum fluviatile; 9.3 to 21 .7% in E. sylvaticum; 8.9 to 14.7% in Carex spp. ; 10.6 to 16.2% in Epilobium angustifolium; 9.4 to 15.2% in Menyanthes trifoliata; 10.3 to 2 5 . 5 % in Potentialla palustris; 11.3 to 23 .0% in leaves of Betulapubescens; 10.1-to 14.7% in B. nana; 15.2 to 19.3% in B. tortuosa; 9.3 to 20 ,2% in Salix pbylicifolia and 6.6 to 14.9% in S. lapponum. The crude protein content varied in different areas and was 2.4. to 4 . 0 % of D M in Cladina rangiferina; 2.2 to 4 . 6 % i n C . mitis; 2.2 to 3 .3% in C . stellaris; 2.0 to 3.2 in Cetraria nivalis and 4.3 to 8.0% in Stereocaulon spp. The mean of crude fibre content was 38 .8% of D M in C . rangiferina; 3 0 . 1 % in C. arbuscula; 39 .8% in C . stellaris and 6.4% in Cetraria nivalis. Lichens contained on average 1.4 to 3 .3% of D M crude fat and 0.4 to 1.8% of D M sugar. Lichens contained few minerals or trace elements. W h e n lichens are digested, negative balances of protein and minerals occur. However , l i chens contain large amounts of easily digestible sugar (mainly l ichenin and isol ichenin) , enabling the reindeer to get the energy they need qu i ck ly in winter. 96 Rangifer, 1986, N o . 1. Appendix

RECONSTRUCTION AND INTERPRETATION OF THE LOCAL VEGETATIONAL SUCCESSION OF A LATEGLACIAL DEPOSIT FROM USSELO (THE NETHERLANDS), BASED ON THE ANALYSIS OF MICRO- AND MACROFOSSILS

Analysis of plant micro- and macrofossils from a sequence from Usselo (The Netherlands) allows a detailed reconstruction of local developments during a period of more than one and a half millennia, starting before the Bølling period and lasting till the end of the Allerød period. The sequence started in an oligotrophic shallow pool with a very low organic production in a barren sandy landscape. An early phase with Gloeotrichia type may be connected with the ability of N-fixation of these blue-green algae. This capacity may have initiated nutrient availability. Characeae played an important role on the initially sandy substrate. These pioneers opened up the site for other aquatics and helophytes, e.g. Potamogeton alpinus, Carex rostrata, Phragmites australis, Equisetumfluviatile, followed by Menyanthes trifoliata, Myriophyllum spicatum and various Carex species. This sequence indicates a gradual eutrophication of the site, accompanied by an increase in production of organic matter (interrupted during the Older Dryas), as substantiated by the organic/inorganic ratio of the substrate. The tendency towards eutrophication ended when the vegetation at the mire surface lost its contact with the ground water. The sequence ended with a vegetation type dominated by Sphagnum and the occurrence of oligotraphentous Thecamoeba. These changes in local vegetation are explicable without resort to temperature fluctuations. The nutrient status of the habitat, and the water level (the latter influenced by sand and organic sediment deposition) were apparently the most important factors in the vegetation succession.

The vegetation and water chemistry of four oligotrophic basin mires in northwestern Ontario

Four small oligotrophic basin mires on the Precambrian Shield were quantitatively analyzed for vegetation patterns and surface water and groundwater chemistry. Mean concentrations of ions in the surface waters of all vegetation stands indicate these mires to be characterized by low calcium content (0.6–1.9 mg Ca L−1), low corrected conductivity (12–31 μmho cm−1 (1 mho = 1 S)), and relatively high pH (4.0–5.7). Mire 224 is dominated by Chamaedaphne calyculata, Scheuchzeria palustris, and Carex oligosperma. The surface water mean determinations are Ca, 1.10 ± 0.51 mg L−1; Mg, 0.57 ± 0.2 mg L−1; corrected conductivity, 16.7 ± 4.2 μmho cm−1; and pH 4.37. Abundance patterns of the dominant Carex species can be correlated with pH of the surface water of the mire. Mire 239 is characterized by Smilacina trifolia, Ledum groenlandicum, and Carex trisperma. The mean surface water determinations are Ca, 1.53 ± 0.36 mg L−1; Mg, 0.59 mg L−1; corrected conductivity, 21.2 ± 2.0 μmho cm−1; and pH 4.0. Significant differences in pH, Ca, and Mg occur between the interior and edge portions of this bog. Water chemistry from portions burned in 1974 showed no difference from unburned portions. The vegetation of mire 661 contains a sequence of communities positioned relative to the inflow streams, with a Myrica gale – Alnus rugosa community followed by a zone dominated by Picea mariana then a Larix laricina zone and then by an open Sphagnum papillosum – Menyanthes trifoliata lake edge zone. More ombrotrophic areas are dominated by Sphagnum fuscum. Ca, Mg, and Fe concentrations, pH, and corrected conductivity were reduced through this sequence. Comparison of weekly samples of water entering and leaving this mire in 1981 showed a reduction of Ca, Mg, SO4, NO3 N, alkalinity, and pH.

Geology and paleoecology of a mid-Wisconsin peat from the Queen Charlotte Islands, British Columbia, Canada

A peat bed on east-central Graham Island of the Queen Charlotte Islands occurs within a nonglacial fluvial succession that is both overlain and underlain by glacial deposits. Radiocarbon dates of 27,500 ± 400 and 45,700 ± 970 yr B.P. at the top and base of the peat, respectively, indicate that it was deposited during the mid-Wisconsin nonglacial interval. The peat is the first documented mid-Wisconsin organic deposit in northern coastal areas of British Columbia. Three local pollen zones are represented. The lowest zone (PM-1) is restricted to sandy silt directly underlying the dated peat. Very high Cyperaceae and moderate Poaceae pollen percentages characterize zone PM-1, and a variety of other herbs are common, suggesting an open landscape rather than a forested one. The middle zone (PM-2) is characterized by abundant pollen of Picea, Tsuga mertensiana, and Cyperaceae, and also contains pollen of Abies, a genus now absent from the Queen Charlotte Islands. Graham Island probably had extensive forests at this time, but abundant pollen and macrofossils of Cyperaceae and emergent aquatics such as Hippuris vulgaris, Veronica scutellata, Potentilla palustris, and Menyanthes trifoliata indicate that there also were open wetland areas. Zone PM-3 also contains abundant arboreal pollen. Large amounts of Sphagnum spores and Selaginella selaginoides megaspores indicate succession of the wetland area at the sample site to a peat bog. Paleoecological analysis of the data suggests that subalpine vegetation elements were depressed by at least 400 m, probably due to a cooler climate. Probable modern analogs in southeastern Alaska and the presence of Abies (probably A. amabilis) indicate that precipitation was higher on eastern Graham Island during the mid-Wisconsin than at present.

Sauerstoffkonsum und Versorgung der Rhizome von Acorus Calamus L., Glyceria maxima (Hartmann) Holmberg, Menyanthes trifoliata L., Phalaris arundinacea L., Phragmites communis Trin. und Typha latifolia L.

Acorus Calamus L., Glycerya maxima (Hartmann) Holmberg, Menyanthes trifoliata L., Phalaris arundinacea L., Phragmites communis Trin. and Typha latifolia have lacunar Systems which allow efficient O2 transport from the surface air to the rhizomes. O2 is supplied mainly by transport through the shoot. The O2 content of the surroundings and, therefore, the O2 uptake through the surfaces of the rhizomes have no influence on the internal O2 concentration. When the rhizomes are detached the internal O2 concentration decreases to the limit of detection despite the air saturated environment. The rate of the O2 decrease is temperature and species dependent.

A late holocene deposit under the Westfriese Zeedijk near Enkhuizen (Prov. of Noord-Holland, The Netherlands): Palaeoecological and archaeological aspects

A Late Holocene lake and peat deposit preserved under the sea dike near Enkhuizen was examined by means of an analysis of both microfossils and macroscopic remains of plants and animals. The hypothesis that the abandonment of Bronze Age settlements in eastern West-Friesland was caused by a rise of the water table was confirmed. This hydrological change was most probably concomitant with the shift towards a more oceanic climate at the Subboreal/Subatlantic transition. The local succession, from the time that the rising of the water table led to a shallow fresh-water pool (viz., ca. 2850 B.P.) until the formation of Sphagnum peat (at ca. 1900 B.P.), could be reconstructed in detail. The gyttja deposited in the initial phase of the section was formed in stagnant, shallow, eutrophic and alkaline water, as is indicated by the presence of some representatives of the Zygnemataceae, Cyanophyceae and Diatomeae. The invertebrates also point to shallow water with a dense stand of vegetation and eutrophic conditions, judging by the presence of Eurycercus lamellatus, Simocephalus sp. and Moina sp. (Cladocera). During the phase in which the open water was gradually filled in by vegetable litter, especially Carex riparia, Lycopus europaeus and Equisetum fluviatile played a prominent part. Subsequently the mesotraphentous Menyanthes trifoliata could settle. The peat deposition continued until the surface had been raised high enough in relation to the water table to permit the establishment of Salix, Thelypteris and Lychnis flos-cuculi. From the subsequent birch carr the succession proceeded to a Sphagnum bog in which Ericaceae played a part. Late Medieval habitation on the oligotrophic bog, which probably began in the eleventh or twelfth century A.D., is reflected, among other things, by the presence of pollen of Secale cereale and Centaurea cyanus and of seeds of Plantago major and some other weeds. The drainage required for habitation and agriculture will have caused subsidence and oxidation of the peat in West-Friesland. In combination with the continuing rise of the sea level during the Late Holocene, this resulted in an increased influence of the sea (in the section this is shown by the occurrence of Salicornia europaea, Puccinellia distans, Triglochin maritima and Foraminifera). A dike was built to protect the cultivated area. In addition to pollen and seeds, more than 100 taxa of other micro- and macrofossils were identified, of which 39 hitherto unrecognized or incompletely known “Types”, predominantly from the gyttja, are described and figured. Among the fossils described are fungal and algal spores, spores of Riccia cf, sorocarpa (Hepaticae), invertebrates, and some Types of unknown origin.

Macrofossils in an interglacial peat deposit at Kap København, North Greenland

Examination two peat samples collected at Kep København, Peary Land, Northgreenland, revealed the presence fo fossils of Betula nana, Menyanthes trifoliata and other plants which do not occur as fao north today. likewise, remains fo Cladocera (e.g. Alonella excisa), beetles (e. g. Gyrinus opacus and Bembidion grapi) and other animals, none of which live in the area today, are present. The occurrence of these fossils, coupled with a radiocarbon date giving an infinite age, suggest that the peat is an interglacials deposit.

Vegetation structure and diversity components of a Fraser estuary tidal marsh

Vegetation data from a predominantly freshwater-influenced tidal marsh in the Fraser River estuary are analysed to investigate different properties of community structure. Three main vegetation zones are recognized, dominated respectively by Carex lyngbyei, Festuca arundinacea, and Menyanthes trifoliata. The zones occupy parts of the marsh which differ primarily in hydrological regime: the Carex zone occurs in regularly flooded and drained areas, mainly along tidal creeks; the Festuca zone occurs on infrequently flooded levees; the Menyanthes zone occurs in areas of impeded drainage, mainly between tidal creeks.Principal components analysis and reciprocal averaging gave similar results except for a 90° rotation of ordination axes. The combined results from cluster analysis and ordination give a useful summary of the marsh vegetation structure. The evaluation of various diversity measures including species richness, species density, beta diversity, and species evenness provided a useful basis for making comparisons and helped to focus attention on factors influencing community development.

STUDIES IN THE VEGETATIONAL HISTORY OF MID‐WALES

SUMMARYStratigraphic and pollen evidence is presented from a mire site on the eastern side of the main Cambrian watershed of central Wales. A complex basin contains Late Devensian lake sediments overlain by Flandrian organic detritus muds. Organic lake muds were replaced by swamp and carr vegetation on the north and west of the site, but the south‐east basin continued as a lake until relatively recent times (the last 200 years). Final colonization of the lake was by a floating raft of Carex rostrata, Menyanthes trifoliata and Sphagnum cuspidatum, on which the present sphagnum‐dominated vegetatiiin has developed. Such schwingmoor mire types are uncommon in Britain and this is a particularly good example.Pollen analysis of the Flandrian lake sediments provides information concerning vegetational history. Interesting early Flandrian records are of Hippophäe rhamnoides. Linum bienne and Fumaria. Pinus sylvestris has low pollen levels in the early Flandrian, unlike many western sites. It is suggested that sites having high values may have Pinus as a local mire colonist. The Ulmus decline is very marked and is accompanied by evidence of cultivation. This is the first evidence of cereal growing in early Neolithic times in Central Wales. Higher in the profile Cannabis saliva assumes importance, possibly as a result of Iron Age/Roman cultivation.

Abscisic acid and the after-effect of water stress on stomatal opening potential

Summary Isolated leaves of ecologically different plants (mesophytes: Pisum sativum L., Helianthus annuus L., Vicia faba L.; hygrophytes: Tradescantia × andersoniana Ludw . et Rohw. , Menyanthes trifoliata L. and Mentha aquatica L.) were wilted for a short time, so that the fresh weight was reduced to 80–60 % of that of the original. Subsequently they were transferred to water for recovery. During the stress period and during the time of recovery, the stomatal pore size and the abscisic acid (ABA) content of the leaves were measured. A delay in the opening reaction of the stomata relative to the recovery of leaf turgor was observed with the mesophytes. The duration of this after-effect of stress on stomatal opening was directly correlated with the ABA level. The ABA level increased two-to five-fold during the stress period and decreased after the stressed leaves had been transferred to water. The application of (±)-ABA to stressed leaves for a duration of one hour after the transfer to water prolonged the duration of stomatal closure, the prolongation being dependent on the concentration applied. The applied ABA increased the ABA level of the leaf and this level decreased subsequently in the same manner as did the natural ABA level. In the hygrophytes investigated, the stomatal opening was not delayed relative to recovery of leaf turgor, and the ABA level did not increase in response to water stress but remained constant ( Menyanthes ) or decreased ( Tradescantia, Mentha ). It is concluded that the after-effect of wilting on stomatal opening is caused primarily by the increased level of ABA. The possible importance of the delay of stomatal opening in the stress physiology of mesophytic and hygrophytic plants is discussed.