Salix Herbacea Research Articles

Plants as Mosaics: Leaf-, Ramet-, and Gender-Level Variation in the Physiology of the Dwarf Willow, Salix arctica

Plant ecophysiological investigations often fail to account for age-specific, tissue-or organ-specific, or life-history-specific effects on overall performance. To address this issue, aspects of gas exchange and water relations of a deciduous and dioecious dwarf willow, Salix arctica, were examined. The degree of physiological variation that occurred as leaves aged was investigated, within and among vegetative and reproductive ramets of a plant's canopy, and between the sexes. Significant differences were observed in rates of photosynthetic carbon assimilation, dark respiration and stomatal conductance, as well as in bulk tissue water relations of leaves at different ages, between reproductive and vegetative ramets within an individual, and between male and female individuals (...)

Stomatal density responds to the glacial cycle of environmental change

Examining the response of stomatal density to past changes in atmospheric CO$\_{2}$ concentration helps us to understand how plants adapted to palaeoenvironmental change, and so helps in predicting their response to future global environmental change. Stomatal density is an important physiological parameter that underpins the productivity of terrestrial vegetation by affecting both rate of carbon uptake and water use efficiency. Previous work on temperate tree species showed a decrease in stomatal density in response to a 60 p.p.m.v. increase in atmospheric CO$\_{2}$ concentration over the past 200 years. However, such a short timespan largely excludes the genetic component of plant adaptation to change in CO$\_{2}$ concentration. We present the first record of stomatal density from fossil leaves extending over 140 ka. Our record for the arctic-alpine dwarf shrub Salix herbacea L. extends back to the penultimate glacial stage, spanning two intervals when atmospheric CO$\_{2}$ concentration was considerably lower (by ca. 170 p.p.m.v.) than at present. Our results demonstrate a decrease in stomatal density in response to long-term increases in atmospheric CO$\_{2}$ concentration, and are in accordance with previous short-term observations and experiments. This implies that relaxation of the stress imposed by low atmospheric CO$\_{2}$ concentration has enabled terrestrial plants to exhibit an adaptive response to the other limiting factor of water availability by reducing stomatal density and hence improving water use efficiency.

Variations in the stomatal density of salix herbacea L. under the changing atmospheric CO 2 concentrations of late- and post-glacial time

The rapidly rising CO 2 concentration of the past 200 years has been shown to be accompanied by a fall in stomatal density in the leaves of temperate trees. The present study attempts to investigate the relationship of atmospheric CO 2 change and stomatal density in the arctic-alpine shrub, Salix herbacea , over the longer time span of 11 500 years offered by fossil leaves from post-glacial deposits. Comparisons of fossil material from Scotland and Norway are made with leaves from living populations growing in Austria, Greenland and Scotland. The Austrian material, from an altitudinal gradient between 2000 and 2670 m above sea level, gives added comparison of contemporary differences of CO 2 partial pressure with altitude. The results of our investigation indicate, rather surprisingly, that the rising CO 2 concentration of the past 11 500 years has been accompanied by an increase in the stomatal density of S. herbacea in contrast to the shorter-term observations on the herbarium material of temperate trees. The most likely explanation appears to centre on the temperatures and water availability of the early postglacial environment overriding the effect of the lower CO 2 regime. However, the scale of the time interval involved may also be significant. Natural selection over the 11 500 year period concerned may have favoured a different response to what is, in effect, an acclimatory response observed in trees within the period of rapid CO 2 rise of the past 200 years.

Intraspecific variation in the water relations of Salix arctica, an arctic-alpine dwarf willow

The seasonal and diurnal water relations were investigated within arctic and alpine populations of the dwarf willow Salix arctica. Marked differences that were habitat dependent (e.g. xeric vs. mesic) occured both within and between the populations. The environmental variables that most affected plant water balance and the bulk tissue water relations were soil water potential (Ψsoil) and the leafto-air water vapor pressure gradient (Δw), however, low soil temperature (<4.0° C) also had a marked effect in the wet to mesic habitats. The effects of declining Ψsoil and increased ‡w were most pronounced in the plants growing in xiric habitats in both populations. Stomatal response to increased ‡w was two-fold greater in alpine versus arctic plants and is hypothesized to have arisen in response to more frequent exposure to the higher evaporative conditions of alpine existance. Seasonal fluctuations in the osmotic potential closely followed changes in Ψsoil, suggesting that these were active rather that passive changes. Additionally, plants from xeric habiats had a lower bulk tissue elastic modulus (more elastic tissues) in both arctic and alpine populations. The osmotic and elastic properties enhanced turgor maintenance over a broad range of leaf water potentials and during periods when ‡w was high. Turgor maintenance also correlated to continued transpiration despite fluctuations in soil and atmospherically induced water deficits. Arctic habitats have a shorter growing season, lower soil temperatures due to the presence of permafrost, but higher soil water potentials and lower leaf-to-air vapor pressure gradients than alpine habitats. The observed variation in patterns of stomatal conductance and in values of tissue water relations characteristics between arctic and alpine populations of S. arctica is hypothesized to have arisen in response to these different environmental regimes which represent different selective regimes that occur along the arctic-alpine environmental continuum inhabited by this wide ranging species.

Patterns of water use and the tissue water relations in the dioecious shrub, Salix arctica: the physiological basis for habitat partitioning between the sexes

Within the high arctic of Canada, Salix arctica, a dioecious, dwarf willow exhibits significant spatial segregation of the sexes. The overall sex ratio is female-biased and female plants are especially common in wet, higher nutrient, but lower soil temperature habitats. In contrast, male plants predominate in more xeric and lower nutrient habitats with higher soil temperatures that can be drought prone. Associated with the sex-specific habitat differences were differences in the seasonal and diurnal patterns of water use as measured by stomatal conductance to water vapor and the bulk tissue water relations of each gender. Within the wet habitats, female plants maintained higher rates of stomatal conductance (g) than males when soil and root temperatures were low (<4° C). In contrast, within the xeric habitats, male plants maintained higher g and had lower leaf water potentials Ψleaf at low soil water potentials and a high leaf-to-air vapor pressure gradient (Δw) when compared to females. Female plants had more positive carbon isotope ratios than males indicating a lower internal leaf carbon dioxide concentration and possibly higher water use efficiency relative to males. Tissue osmotic and elastic properties also differed between the sexes. Male plants demonstrated lower tissue osmotic potentials near full tissue hydration and at the turgor loss point and a lower bulk tissue elastic modulus (higher tissue elasticity) than female plants. Males also demonstrated a greater ability to osmotically adjust on a diurnal basis than females. These properties allowed male plants to maintain higher tissue turgor pressures at lower tissue water contents and Ψsoil over the course of the day. The sex-specific distributional and ecophysiological characteristics were also correlated with greater total plant growth and higher fecundity of females in wet habitats, and males in xeric habitats respectively. The intersexual differences in physiology persisted in all habitats. These results and those obtained from growth chamber studies suggest that sex-specific differences have an underlying genetic basis. From these data we conjecture that selection maintaining the intersexual differences may be related to different costs associated with reproduction that can be most easily met through physiological specialization and spatial segregation of the sexes among habitats of differing conditions.

A Wisconsinan interstadial arctic flora and insect fauna from Clarksburg, southwestern Ontario, Canada

Radiocarbon dating and sedimentological, pollen, plant macrofossil, and insect analyses were performed on a subtill organic deposit in southwestern Ontario, Canada. Stratigraphic relationships and minimum radiocarbon dates suggest a Middle Wisconsinan age. The sedimentary sequence indicates a fluvial environment with a rising base level as an approaching ice-front dammed and produced a deepening proglacial lake. Eventually ice covered the site for much of Late Wisconsinan time. The fossil plants and insects indicate an open-ground, treeless landscape comparable to modern low to high arctic environments in Canada. The beetle fauna is dominated by members of the sub-genus Cryobius, and is associated with fossils of dwarf shrubs, Salix herbacea and Dryas integrifolia, and herbs such as Saxifraga oppositifolia.

Influence of Climate and Age on Annual Shoot Increment in Salix Herbacea

(1) Shoots of the dwarf shrub Salix herbacea were collected from three alpine snow-bed sites in northern Sweden. Multiple regression analysis was used to examine the importance of shoot age, mean monthly temperature and precipitation in determining annual shoot increment. (2) Shoot age accounted for 39-48% of the within-shoot variation in length of the annual stem segments, which showed a logarithmic decline throughout the life-span of the shoot. (3) Climatic variables contributed little to the total variation in annual increment. However, temperatures during the intense snow-melt period (May and June) during the year before growth, accounted for about 80% of the between-year variation in two of the three samples. This suggests that growing season length limits the carbohydrate stores available for the following year's shoot increment.

Pollen analysis of postglacial sediments from Eildun Lake, District of Mackenzie, N.W.T., Canada

Sediment from Eildun Lake, located at 63°8.6′N, 122°46.5′W in the northern boreal forest, was cored to a depth of 268 cm and analyzed for pollen content. Pollen percentages and 14C dates suggest a vegetational sequence extending back over 11 000 years. The sequence begins with a discontinuous herb tundra dominated by Artemisia and Gramineae. This was succeeded by a shrub tundra dominated by dwarf birch and willow. Poplar had invaded by approximately 10 700 BP to form a dwarf birch – poplar groveland or forest tundra. Between approximately 10 300 and 7510 BP spruce replaced poplar as the dominant tree, although still forming a forest tundra. Boreal forest, including tree birch and alder, became established shortly after 7510 BP and has persisted since then with very little change. Pinus pollen has increased in percentage, particularly during the last 2400 years, reaching its Holocene maximum at the present day. The percentages attained indicate the presence of pine trees regionally though not in the near vicinity of Eildun Lake.

Chromosome numbers of flowering plants from northern Norway and Svalbard

Chromosome numbers of 25 taxa of flowering plants from northern Norway and Svalbard are reported. Four species and one subspecies, Carex halophila F. Nyl. (2n = ca. 78), C. stenolepis Less. (2n = ca. 80), Salicorniapojarkovae N. Sem. (2n = 36), Alnus incano (L.) Moench ssp. kolaensis (Orlova) Love (2n = 28), and Saxifraga svalbardensis D. O. Øvstedal (2n = ca. 64), have not been studied karyologically before. Chromosome numbers of four additional species are reported for the first time from Norway; those of another six species for the first time from northern Norway. The hybrid Salix herbacea L. (2x) x 5. polaris Wahlenb. (6x) is proved tetraploid and may be fertile. A possible hybrid between Saxifraga hyperborea R. Br. and S. rivularis L. was revealed.

Ectomycorrhizal fungi of Salix rotundifolia III. Resynthesized mycorrhizal complexes and their surface phosphatase activities

Pure culture isolates were obtained from fungi fruiting in the vicinity of dwarf willows at Barrow and Cape Simpson, Alaska. Four of these isolates and one isolate from Maryland were tested for their ability to form ectomycorrhizae with cuttings of Salix rotundifolia under controlled environmental conditions. Isolates of Entoloma sericeum, Hebelomapusillum, and Cenococcum geophilum from Barrow and Cape Simpson, Alaska all formed typical ectomycorrhizae with S. rotundifolia, while an isolate of C. geophilum from a temperate ecosystem (Maryland) did not.All of the ectomycorrhizae synthesized with S. rotundifolia, plus uncolonized roots, demonstrated an ability to hydrolyze p-nitrophenyl phosphate at a pH of 4.7. The acid phosphatase activity of E. sericeum ectomycorrhizae was from 10 to 40 times as great as that demonstrated by other mycorrhizal and nonmycorrhizal roots on a surface area basis.

Alpine lichen-dominated communities in Alberta and the Yukon

Alpine lichen-dominated vegetation is described with emphasis upon floristic composition, quantitative structure, and distribution of lichen communities. Macrolichens and vascular plants were quantitatively sampled using stratified random quadrats (10 cm × 40 cm) in 40 stands (30 m × 5 m) in west-central Alberta and north central Yukon Territory. Comparable acid and basic substrates, and glaciated and unglaciated sites were sampled in each region. Bray-Curtis and reciprocal averaging ordinations were used to analyze vegetation data. For both macrolichens and vascular plants, floristic similarity is greater within each region than on equivalent substrates in different regions. Three alpine macrolichen communities are described in each region which exhibit pronounced regional differences. Cetraria tilesii and Thamnolia subuliformis characterize driest sites in both regions, while Cetraria cucullata indicates mesic habitats. Cladonia spp. dominate acidic Yukon sites; Stereocaulon alpinum and Peltigera aphthosa characterize equivalent Alberta habitats. Vascular plant communities are dominated by Dryas integrifolia and D. octopetala in Alberta and Yukon areas, respectively, with dwarf willow and heath in acidic, mesic sites. Distribution of alpine communities of macrolichens and corresponding vascular plants is more strongly correlated with substate pH and moisture, than with glaciation history. Comparison with other northern studies suggests that these macrolichen communities may be found throughout the Canadian Cordillera where equivalent habitats are present.

MODERN POLLEN SAMPLES FROM WEST GREENLAND AND THE INTERPRETATION OF POLLEN DATA FROM THE BRITISH LATE‐GLACIAL (LATE DEVENSIAN)

SummarySamples of the modern pollen rain, some from lake sediment and some from moss polsters, were taken in two regions of West Greenland in which the climate is respectively low arctic continental and low arctic oceanic: (1) round the head of Söndre Strömfjord at 67° N; and (2) the south‐west of Disko Island at 70° N. The vegetation has been described and analysed by Böcher (1954, 1959, 1963). In Region 1 where the vegetation is a mosaic of xerophilous grassland with Artemisia borealis (steppe) and Betula nana heath, mean pollen percentages from 11 polsters corresponded quite closely with percentage cover for those taxa in the vegetation. Polsters from steppe could be distinguished from heath polsters by higher values for Artemisia in steppe and Ericales (Ledum, Empetrum, Vaccinium, Rhododendron) in heath, but Betula nana and grasses, with the highest values in both pollen and vegetation, showed no consistent difference between polsters of different origin‐presumably showing good pollen dispersal. In four lake samples B. nana was over‐represented by pollen values and Artemisia had a lower mean than in terrestrial samples. In Region 2 where the vegetation is a more oceanic heath in which B. nana is infrequent and Artemisia absent, the pollen samples differ from those of Region 1 in consistently higher values for Cyperaceae and lower values for Gramineae and B. nana: Artemisia is here represented by only the same few grains as the exotic taxa Pinus and Picea. When compared with vegetation cover in Region 2, sedges and B. nana appear to be over‐represented in pollen samples, especially from lakes, and Salix herbacea and the herbs of snow‐bed and heath‐mat communities to be under‐represented.These findings can be used in interpretation of Late Devensian pollen spectra which lack arboreal pollen, and make it probable that: (i) samples from the earliest Late Devensian pollen zones represent an oceanic dwarf‐shrub vegetation in which there was more Salix herbacea and fewer sedges than pollen values suggest; (ii) Betula nana did not at any time form an appreciable part of the vegetation cover; and (iii) Artemisia pollen values provide an index to local vegetation cover, which implies a vegetation mosaic correlated with snow cover during the period of the Loch Lomond Advance (c. 11000 to 10500 B.P.).

Paleobotany of Wisconsinan interstadials, eastern Great Lakes region, North America

This study concerns the pollen and plant macrofossils from Mid-Wisconsinan Interstadial sites within the Wisconsinan ice margin in eastern North America. The time period covered is from about 55,000 years BP to 22,500 years BP, an interval much longer than the postglacial. Sediments examined are principally those of large lakes deposited in the Erie and Ontario basins during intervals of ice retreat. The Port Talbot I Interval (from about 55,000 to 50,000 years BP) in the Erie basin is characterized by pollen assemblages alternating from Pinus-dominated zones to ones with abundant Pinus, Quercus, and nonarboreal pollen. These assemblages are interpreted as indicating relatively warm and dry conditions. Mean July temperatures fluctuated between 15 and 21°C. During the succeeding Port Talbot II Interval and Plum Point Interstadial, in both the Erie and Ontario basins, pollen assemblages are characterized by dominant Pinus and Picea. Characteristic macrofossils include needles of the boreal Picea and Larix and leaves of species with a more northerly distribution, such as Dryas integrifolia, Betula glandulosa var. glandulosa, Vaccinium uliginosum var. alpinum, and Salix herbacea. These fossil assemblages are interpreted as indicating cooler and moister conditions in a forest-tundra environment. Mean July temperatures fluctuated between 10 and 15°C during the Port Talbot II Interval and Plum Point Interstadial.

Energy Budget and Growth during the Development of Melasoma collaris (Coleoptera)

Ingestion, egestion, production (growth) and respiration were determined for all developmental stages of the Chrysomelid beetle Melasoma collaris L. fed Salix herbacea L. Gross efficiency of growth (100 x growth/ingestion) for the three larval instars were 32, 31, and 22, totally 24% (energy); and 26, 27, and 20, totally 21 % (dry weight). Assimilation efficiency (100 x assimilation/ingestion), based on collections of excrement, was 76, 77, and 65 % (energy) in the larval instars. Respiration calculated from the energy ingested, egested and stored as growth, was about 2-6 times higher than measured by respirometers.

MODERN POLLEN RAIN STUDIES IN ICELAND

SUMMARYThe relationship between modern pollen rain and the floristic composition of vegetation was studied for six vegetation types in Iceland, viz. fell‐field, Rhacomitrium heath, grassland with dwarf‐shrub, dwarf‐shrub heath, mires within dwarf‐shrub heath, and a Salix herbacea‐ dominated slope. The results suggest that the vegetation types examined can be characterized, to some degree, by their modern pollen rain.

Late Pleistocene floras from Earith, Huntingdonshire

A pit in fluviatile gravel of the River Ouse at the western edge of the East Anglian fenland has exposed several richly organic beds of Last-glacial age. A radiocarbon date of 42 000 years from one bed confirms the terrace stratigraphy in placing the beds in a fairly early part of the Weichselian. The organic beds are succeeded by cryoturbation phenomena and ice wedge casts, indicating a severely cold climate with permafrost. The beds represent former pools on the flood-plain into which plant detritus was washed from the surroundings, chiefly by melt water in the spring. Pollen is sparse, but the macroscopic plant remains indicate a vegetation dominated by dwarf willows, accompanied by many herbs of base-rich, open habitats. Identification of the macrofossils is discussed and comments are made on the ecology and taxonomy of important species. The flora contains a mixture of northern and southern distributional types, the southern including species requiring a July mean temperature approaching 16 °C. Halophytes are frequent, and four species are considered to be obligate halophytes and to demonstrate the presence of salt in the substrate. The plant mixtures are explained as a result of the peculiarly open habitats of the glacial landscape and of the climate, which appears to have had warm summers and very cold winters, with a mean annual temperature slightly below 0 °C, resulting in discontinuous permafrost.

LATE-GLACIAL POLLEN AND PLANT MACROFOSSILS FROM SPIDER CREEK, SOUTHERN ST. LOUIS COUNTY, MINNESOTA

Paleobotanical analyses of basal sediments in the Spider Creek drainageway, southern St. Louis County, Minnesota, suggest a late-glacial tundra vegetation which was rapidly invaded by boreal forest at the beginning of the postglacial period. The tundra is inferred mainly from plant macrofossils which include leaves, seeds, or fruits of such arctic plants as Dryas integrifolia, Salix herbacea, Vaccinium uliginosum var. alpinum, Juncus balticus, Arenaria cf. humifusa, Rhododendron lapponicum, Stellaria humifusa type, Potentilla nivea, and Carex capillaris. The pollen diagram (Pl. 1) shows a late-glacial sequence typical of northeastern Minnesota, with high abundances of nonarboreal pollen, Picea, and Cyperaceae. The beginning of the postglacial period is marked by a sudden disappearance of all arctic macrofossils and a concomitant appearance of Picea and Larix needles. On the pollen diagram arboreal pollen and Picea increase in abundance, Cyperaceae decreases, and Betula forms a prominent peak. Correlation with other pollen diagrams from northeastern Minnesota indicates that the late-glacial sediments were deposited between 12,000 and 10,500 years ago. Pollen and plant-macrofossil analyses indicate that boreal forest covered all but northeastern Minnesota during this time; environmental conditions apparently were not suitable for a forest cover there during the early stages of glacial retreat.

Late-Weichselian conditions in south eastern Britain: organic deposits at Colney Heath, Herts

Peat erratics in gravel at Colney Heath, near St Albans, have been shown to have a radio-carbon age of 13560 years ± 210. Detailed pollen analyses, identifications of macroscopic plant remains and identifications of Bryophyta are now presented and linked with reports upon Coleopteran remains already published. These results are shown to be closely similar to those of other river terrace deposits of the region including the Lea Valley Arctic Plant Bed, the Barnwell Station Plant Bed, and stages of the Nazeing (Lea Valley) deposits. Radiocarbon dates place all these within the late Weichselian and it appears that all were formed and preserved by temporary and local changes in the valleys, rather than as a result of general climatic shift. They may be taken to reflect the general late-Weichselian fauna and flora that persisted south of the ice-sheets in Britain during the later part of the last glaciation, and they are the antecedent stage to the now well-known late-Glacial Period. The late-Weichselian vegetation of this region was apparently without woodland, although dwarf shrubs including arctic birch and dwarf willows were abundant, there was a considerable variety of dry-land plants, including many heliophytes and plants of open ground, and aquatic and marsh plants were present in abundance and variety. The plant lists include many of strongly northern or arctic alpine range, but there are already present a few species with decidedly southern range, as well as many widely ranging species. A few species of both oceanic and continental range are also present. The plant evidence accords with that from the animal remains.

On the Peri-Glacial Flora of Jæren. With Notes on the Morphology of the Salix Pollen Grain

In 1935 I published a pollen spectrum from Brondmyra (Jaeren) about which I in 1950 (p. 37) wrote that it had been interpreted as indicating extreme snow-patch vegetation dominated by Salix herbacea «and that interpretation has not been challenged so far». However, no one could realise more lively than I have done myself, that the interpretation was based upon rather indirect evidence, and that a re-examination of the spectrum in question would be desirable. Pollen analysis has made some progress since 1935 (when many workers still did not distinguish between Salixand Artemisia pollen), and the more acute morphological analysis of to-day might give information which was then concealed. I feel that if a pollen analyst should contribute to a presentation volume to our senior glaciologist, few themes could be more appropriate than this pollen spectrum from the edge of the vanishing Ice Age glacier — provided the former interpretation can still be retained.

Some Scottish mountain rust fungi

Infection experiments were performed with Melampsora epitea from Saxifraga hypnoides , and with Melampsora epitea var. reticulata from Saxifraga aizoides to ascertain the uredo-, and the teleutospore hosts. The experiments showed that the rust on S. hypnoides infects Salix herbacea and some of its hybrids. The rust on Saxifraga aizoides infected only Salix reticulata . The uredo paraphyses produced on Salix reticulata were larger than those for typical Melampsora epitea but fitted those of M. epitea var. reticulata . The uredo paraphyses on Salix herbacea and hybrids were typical of Melampsora epitea. M. arctica and M. alpina are considered indistinguishable from M. epitea . Observations show that M. epitea var. reticulata may perennate as mycelium in the Saxifraga host and the relation of this habit to dispersal and distribution in the field is mentioned.