The nitrogen economy of mountain birch seedlings: implications for winter survival

1 Seedlings of mountain birch Betula pubescens ssp. czerepanovii were grown outdoors, under different environmental conditions, during their first growing season at Abisko, northern Sweden. Winter survival of seedlings was studied in relation to their growth and nitrogen (N) acquisition rate during the previous growing season.
2 Effects of fertilization and soil temperature on seedling growth and N acquisition were analysed in a factorial experiment including seven fertilizer levels and two temperature treatments. Effects of shading and neighbours ( B. p. ssp. czerepanovii and Empetrum hermaphroditum ) on seedling growth and N economy were evaluated in another experiment including five different neighbour interaction treatments.
3 An increase in either soil temperature or fertilization rate caused the birch seedlings to take up more N and grow faster. The relative growth rate and rate of N accumulation during the 12-week growing season were closely related to winter survival: at a relative growth rate of 2.0% and 3.8% day⁻¹, the winter survival of mountain birch seedlings was estimated to be 5% and 95%, respectively. This range corresponded to a relative N accumulation rate between 2.4% and 4.3% day⁻¹.
4 The relative N accumulation rate was clearly reduced by shading and by the plant–plant interactions studied. The effects of shading and birch neighbours but not of Empetrum on the rate of N accumulation could be explained by lower soil temperature.
5 Nutrient supply, soil temperature, vegetation shade and, presumably, allelopathy affect the N acquisition of first-year mountain birch seedlings, and thus also influence their winter survival. Soil temperature might be the major influence on the survival rate, due to its strong influence on the root N uptake rate.     

Circumpolar size variation in the skull of the arctic fox Alopex lagopus

Eleven skull and mandible dimensions were measured in arctic foxes, Alopex lagopus, from Fennoscandia, the Far East (Siberia), Baffin Island (Canada), Greenland, Jan Mayen and Svalbard (n=278), and comparisons with data from the literature were made, including samples from most parts of the species' circumpolar range. Significant differences between regions were found, notably Fennoscandian and Siberian foxes were larger than foxes from Greenland, Jan Mayen and Svalbard. Overall skull size was reduced with increasing latitude, which may indicate energetic constraints on body size in high latitudes due to a lower primary productivity.     

Movements and diving of bearded seal (Erignathus barbatus) mothers and pups during lactation and post-weaning

Eleven bearded seals (Erignathus barbatus) were tagged with satellite-linked dive recorders in Kongsfjorden, Svalbard, Norway, in May 1994. These animals included four mother-pup pairs and three single pups. The seals were tracked for 21–258 days. A total of ˜207,000 dives were recorded. Bearded seal mothers showed limited movements during the nursing and moulting periods. After weaning, the pups moved out of the tagging area and dispersed coastally. One pup left Svalbard and moved far offshore to Greenland and Jan Mayen. Bearded seal adults displayed a bi-modal dive behaviour, with peaks of activity that were shallower than 10 m or from 50 to 70 m. Most dives for adult seals (97%) were shorter than 10 min. Young pups performed dives that were shallower and shorter in duration than their accompanying mothers, but diving skills improved rapidly with age. Six of the seven pups dived deeper than 448 m by the time they were 2 months old. Analyses of movement data with respect to separation of mother-pup pairs suggest a lactation period of about 24 days. Accepted: 31 January 2000     

Litter of the hemiparasite<Emphasis Type="Italic"> Bartsia alpina</Emphasis> enhances plant growth: evidence for a functional role in nutrient cycling

Hemiparasitic angiosperms concentrate nutrients in their leaves and also produce high quality litter, which can decompose faster and release more nutrients than that of surrounding species. The impact of these litters on plant growth may be particularly important in nutrient-poor communities where hemiparisites can be abundant, such as the sub-Arctic. We tested the hypothesis that plant growth is enhanced by the litter of the hemiparasite Bartsia alpina, in comparison with litter of co-occurring dwarf shrub species, using a pot based bioassay approach. Growth of Betula nana and Poa alpina was up to 51% and 41% greater, respectively, in the presence of Bartsia alpina litter than when grown with dwarf shrub litter (Vaccinium uliginosum, Betula nana and Empetrum nigrum subsp. hermaphroditum). The nutrient concentrations of Betula nana plants grown with Bartsia alpina litter were almost double those of plants grown with dwarf shrub litter, and a significantly greater proportion of biomass was allocated to shoots rather than roots, strongly suggesting that nutrient availability was higher where Bartsia alpina litter was present. The presence of litter from dwarf shrubs, or the moss Hylocomium splendens, did not reduce the positive effect of Bartsia alpina litter on plant growth. E. nigrum litter did not appear to affect plant growth substantially differently from litter of other dwarf shrub species, despite earlier reports of its allelopathic action. The enhanced nutrient uptake and growth of plants in the presence of Bartsia alpina (and potentially other hemiparasitic species) litter could have important implications for communities in which it occurs, including enhanced survival of seedlings of co-occurring species and increased resource patchiness.     

Building an indicator to characterize the thermal conditions for plant growth on an Arctic archipelago,Svalbard

Plant growth in the Arctic is strictly dependant on thermal conditions. The purpose of our study is therefore to calculating temperature distributions on the Svalbard archipelago at a relatively high spatial resolution. The model is designed to reflect both the length of the growing season and the temperature sum for a given area (i.e. growing degree-days (GDD)). GDD on Svalbard is defined as the cumulative sum of positive mean daily temperatures in the months of June, July and August. The temperature distribution of GDD for the entire archipelago is calculated from both local and regional information. Local information is derived from data collected in a small area in northwestern Spitsbergen (Kongsfjorden) where a network of 45 thermal sensors recorded air temperatures for five years (2001–2005). A local GDD parameter is computed by a linear combination of elevation, valley depth and NDVI (normalized difference vegetation index). Then this local GDD is applied to the whole of Svalbard (GDD1) and refined stepwise by adding environmental variables such as cloud fraction, land surface temperature, sea surface temperature, distance to the ocean and number of snow-free days. Because the official network of climatological stations on Svalbard is not dense enough and sufficiently well-distributed across the archipelago to enable spatial interpolations for four years only (2011–2014), all outputs are statistically evaluated and adjusted using the values recorded at 9 (2011), 12 (2012) and 13 (2013–2014) meteorological stations (GDD_ref) and used as a set of evaluation data. The final model (GDD_mean), which is the mean of the annual models estimated by regression (GDD_est), performs well: the central parts of Spitsbergen, known for its comparatively high temperatures, contrast with the colder northern and eastern parts of the archipelago.     

Local variation in arctic fox abundance on Svalbard,Norway

Arctic fox (Alopex lagopus) numbers vary greatly, with cyclic fluctuations often associated with fluctuations in microtine rodents. However, in areas where small prey mammals are absent, such as Iceland and Svalbard, such cyclic fluctuations are lacking. Annual fluctuations in the density of the arctic fox population on the Brøggerhalvøya peninsula and Kongsfjorden region on Svalbard, Norway, were studied from 1990 to 2001 by using indices of fox abundance. All indices showed similar trends; fox numbers were low in 1990, increased until 1995 whereupon they decreased sharply, before increasing again and levelling off in 2001. Increasing numbers of foxes during the first part of the study paralleled increasing numbers of Svalbard reindeer (Rangifer tarandus platyrhynchus) carcasses in winter and increasing numbers of nesting barnacle geese (Branta leucopsis) in summer. This study shows that the number of arctic foxes varies greatly even in areas without fluctuating microtine rodents.     

Frugivory and seed dispersal by redwings Turdus iliacus in southwest Iceland

We studied consumption of wild fruits by redwings Turdus thacus coburnt at two sites on the southwest coast of Iceland, just prior to the autumn migration During this period the principal study site offers c 800000 fruits ha⁻¹ most of these are of Empetrum nigrum (c 90% of fresh weight), but fruits of Vaccimum uliginosum. Arctostaphylos uva-ursi, Vaccimum myrtillus and Rubus saxatilis are also present Redwings regularly consumed the fruits of all these species except R saxatilis At both study sites E nigrum fruits were the most important component of the redwing diet (70 - 80% of fruits ingested), followed by V uliginosum (c 20%) Neither species was consumed as predicted on the basis either of overall relative abundance of fruits or of relative frequency of occurrence of fruiting plants in two hundred 0 3 m² plots In another forty 0 3 m² plots, the number of E nigrum fruits consumed over a seven-day penod was not significantly correlated with the number of fruits initially present Empetrum nigrum seed width is positively correlated with fruit size, and the mean width of seeds in droppings suggests that redwings prefer large E nigrum fruits (which have a higher pulp-to-seed weight ratio) to small E nigrum fruits Despite the predominance of E nigrum, redwing droppings tend to contain a mix of seeds of different species, the most frequent combination being E nigrum and V uliginosum     

Topographic and altitudinal patterns in plant communities on European arctic islands

 Vegetation on Bear Island, Jan Mayen and Spitsbergen was investigated along altitudinal and topographic gradients in order to describe the main patterns in plant community distributions and compare them with those on the mainland. In a numerical classification the communities were distinctly differentiated; however, physiognomically similar Racomitrium and Sanionia communities dominated in most habitats on Bear Island and Jan Mayen. On Spitsbergen, moss-dominated communities prevailed in depression sites. High-altitude sites were occupied either by moss-dominated communities or by variable assemblages of fragmented moss cover and scattered vascular plants. Dwarf shrub and grass heaths that were common on the mainland did not occur on grazer-free Bear Island and Jan Mayen, and were confined to the lowest altitudes on Spitsbergen. The lack of grazers on Bear Island and Jan Mayen accounts in part for the differences in vegetation between the mainland and the islands. Received: 13 December, 1995/Accepted: 13 March, 1996     

Short-term effects of simulated environmental change on phenology, leaf traits, and shoot growth of alpine plants on a temperate mountain, northern Japan

In order to assess the responses of circumpolar and semicircumpolar plants growing around their southern distribution margins to artificial warming, we set up 11 open-top chambers (OTCs) on a fell-field (1680 m a.s.l.) in the Taisetsu Mountains, northern Japan. The OTCs increased mean air temperature by 1.3°C through the growing season (June–September) and extended the length of the growing season. We examined phenology and leaf traits of plants in the OTCs and control plots during the first season under artificial warming treatment using two deciduous and three evergreen species. Ledum palustre (evergreen shrub), Vaccinium uliginosum , and Arctous alpinus (deciduous shrubs) showed earlier leaf emergence and/or flowering in the OTCs. Deciduous shrubs had longer individual leaf longevity and an extended foliage period in the OTCs than in the control plots. There were no significant differences in specific leaf area and leaf size for many species between the OTCs and the control plots. Vaccinium vitis-idaea (evergreen shrub), L. palustre, A. alpinus , and Empetrum nigrum (evergreen shrub) had lower leaf nitrogen concentration in the OTCs than in the control plots, whereas it was higher in V. uliginosum . Only E. nigrum showed larger annual shoot growth in the OTCs. No clear differences in response to the warming effect were detected between evergreen and deciduous species in the first season. Circumpolar plants growing in temperate alpine regions may be more affected by season length rather than temperature itself.     

A study of Draba cacuminum (Brassicaceae)

A morphological analysis of the Scandinavian mountain endemic Draba cacuminum Elis. Ekman is presented, based on Scandinavian herbarium collections and a population sample from the Finse area, S Norway. It is compared with supposedly close relatives, especially D. norvegica Gunnerus, and is found to be a distinct species with infraspecies variation at two levels. The populations of southern and northern Scandinavia have been separated as subspecies, ssp. cacuminum and ssp. angusticarpa Elven ssp. nov., respectively, and there is also variation within the southern subspecies. A lectotype has been chosen for D. cacuminum , a revised distribution map is presented, and the ecology and phytogeography of the species is discussed. It seems to be a weak competitor, and its present very discontinuous area is assumed to be a remnant of one continuous or more probably two areas (in S Norway and N Scandinavia) in the late Weichselian.     

Seedling density and seedling survival in Alaskan cotton grass tussock tundra

Previous workers have suggested that reproduction by seedling establishment is less important in the maintenance of tundra vegetation than in temperate areas, but few quantitative data are available. Seedling densities were studied at 11 tundra sites in or near disturbed and undisturbed cotton grass tussock tundra in Alaska, and numerous seedlings were found. Examination of seedling age structures suggests that at least Ledum palustre and probably also Empetrum nigrum do replace themselves by seed in undisturbed tundra. Seedling densities vary greatly depending on the substrate available for establishment.     

Micro-site performance of evergreen and deciduous dwarf shrubs in a subarctic heath in relation to nitrogen status

The relationship between micro-site nitrogen status (total soil N conc., total vegetation N, and leaf N conc.) and performance (biomass) for two evergreen and two deciduous dwarf shrubs was studied in a subarctic heath. One deciduous species, Vaccinium uliginosum , dominated on sites having the highest vegetation nitrogen content and highest leaf nitrogen concentrations. The evergreen Empetrum hermaphroditum dominated on sites with a low total vegetation nitrogen content and low leaf nitrogen concentrations. Two other species, V. myrtillus (deciduous) and V. vitis-idaea (evergreen), showed intermediate patterns that were not clearly separated from either V. uliginosum or Empetrum . Soil nitrogen content showed no significant differences between micro-sites. Possible physiological reasons for the observed patterns are discussed.     

Summer food of the golden plover Pluvialis apricaria at Hardangervidda, southern Norway

Golden plover stomachs were examined through the breeding season al Hardangervidda, southern Norway. The main foods were Diptera larvae (in particular Tipula excisa ), adult Coleoptera (notably Otiorrhynchus dubius and Carabidae), and in May and August berries of Empetrum hermaphroditum. Also some larvae of Coleoptera and Lepidoptera were taken. Adult Coleoptera were considerably more common in the diet than expected from abundance data, while Araneae were unimportant as food in spite of a high abundance. The males take the major parental duties after hatching, allowing the females a more undisturbed feeding, supposed to be strongly advantageous for them due to close proximity of egg-laying and the start of the postnuptial moult. This is reflected in the diet: in July males showed a larger tropic diversity, and ate more adult insects and less insect larvae than the females.     

Effects of enhanced UV-B radiation and elevated carbon dioxide concentrations on a sub-arctic forest heath ecosystem

An experiment is described which studies the effects of enhanced UV-B radiation (simulating a 15% reduction in the Ozone layer) and elevated atmospheric concentrations of CO₂ (600 ppm) on the dwarf shrub layer of a sub-arctic forest heath ecosystem at Abisko, North Sweden. The experimental treatments were first applied in 1993, and have covered most of the snow-free season (late May to early September) 1993–1995. Effects of the treatments on the four dwarf shrub species have been recorded largely using non-destructive measures (Vaccinium uliginosum, Vaccinium myrtillus – deciduous species and Vaccinium vitis-idaea and Empetrum hermaphroditum – evergreen species). Effects of the treatments on stem growth and leaf thickness have so far been small, although CO₂ treatments initially stimulated stem extension in Vaccinium myrtillus 1993 and depressed growth in V. vitis idaea in 1994 and E. hermaphroditum during 1995. UV-B treatments stimulated fruit production in V. myrtillus in both 1994 and 1995, but there was no effect on reproductive phenology. There were also marked effects of UV-B treatments on insect herbivory in the deciduous dwarf shrubs; with leaf area loss being greater than the control in the UV-B treatment in V. myrtillus and less in V. uliginosum. The results point to the possibility of important effects of the treatments on physiological and chemical processes within the plants. The ecological results of such effects may not be immediately apparent, but may be far reaching, pointing to the need for long-term in situ experimentation in predicting the effects of these global change variables.     

Arctic alpine vegetation change over 20 years

Recent arctic warming experiments have recorded significant vegetation responses, typically an increase in shrub cover and a loss of species richness. We report similar changes in vegetation along an arctic mountainside in northern Sweden over 20 years. During this time mean annual temperature increased by 2.0 °C, and growing season temperature by 2.3 °C. Growing season length increased by 28% at the bottom of our study area, in birch forest, and by 175% on the mountaintop. Neither total vegetation cover nor the cover of bare ground changed. One common dwarf shrub, Empetrum hermaphroditum , and two common forbs, Viola biflora and Geranium sylvaticum , increased in abundance over time, but no common species moved up the gradient. Species richness declined significantly over time, with an average loss of two species per 50 cm × 100 cm plot. The richness of herbaceous species at intermediate altitudes decreased significantly with increasing shrub cover. In spite of large changes in temperature, the type and magnitude of vegetation change along this mountainside were relatively modest and consistent with those from wide-spread warming experiments.     

气候变化对我国7种植物潜在分布的影响

利用CART(分类和回归树)模型及A2和B2气候情景,模拟分析气候变化对瘿椒树、岩高兰、延龄草、星叶草、天麻、蝟实和秃杉分布范围及空间格局影响.结果显示:气候变化下,就目前适宜分布范围,瘿椒树呈增加趋势,其它植物呈缩小趋势;就新适宜及总适宜分布范围,蔚实、延龄草和瘿椒树呈增加趋势,星叶草和岩高兰呈减小趋势,天麻和秃杉在...     

Population dynamics of Empetrum hermaphroditum (Ericaceae) on a subarctic sand dune: Evidence of rapid colonization through efficient sexual reproduction

The importance of sexual reproduction for clonal plant species has long been underestimated, perhaps as a consequence of the difficulty in identifying individuals, preventing the study of their population dynamics. Such is the case for Empetrum hermaphroditum, an ericaceous species, which dominates the ground vegetation of subarctic ecosystems. Despite abundant seed production, seedlings are rarely observed. Therefore, prevalent seedling recruitment on a subarctic dune system provided an opportunity to study the population dynamics and spatial pattern of the colonization phase of this species. We established a 6-ha grid on the dune systems that extended from the shoreline to the fixed dunes and mapped and measured all E. hermaphroditum individuals in the grid. Moreover, we sampled 112 individuals just outside the grid to identify any allometric relationship between the size and age of the individuals, which allowed us to reconstruct population expansion. The overall size structure suggests that the population is still expanding. In the last 50 yr, E. hermaphroditum advanced more than 200 m in the dune system. Expansion started in the 1960s simultaneously at different distances from the shoreline. Colonization did not proceed gradually from the fixed dune toward the shoreline but instead individuals established earlier in the troughs between the dunes, with an increasingly clumped spatial pattern as the population filled in with time.     

Prevalence of antibodies against Toxoplasma gondii in polar bears (Ursus maritimus) from Svalbard and East Greenland

Serum samples from 419 polar bears (Ursus maritimus) from Svalbard and the Barents Sea (collected 1990-2000) and 108 polar bears from East Greenland (collected 1999-2004) were assayed for antibodies against Toxoplasma gondii using the modified agglutination test. Antibody prevalences were 3.6% among cubs dependent on their mothers and 21.4% among subadults and adults. Among subadults and adults there was an interaction between population and sex, with similar prevalences among females (Svalbard = 19.5%, Greenland = 18.0%), but a high frequency among Svalbard males (28.7%) as compared to Greenland males (5.8%). The pattern was also significant after correcting for differences in age distribution. The sex-population interaction term is believed to be connected to area- and sex-specific feeding ecology. The prevalences of antibodies against T. gondii in Svalbard and Greenland were high compared to previously reported findings in polar bears from Russian and Alaskan areas.     

Alpine and Arctic tundra shrub populations show similar ontogenetic growth trends but differing absolute growth rates and lifespan

The majority of terrestrial primary production is performed by plants, the ontogenetic growth trends of which significantly influence biomass and carbon dynamics. Here, we present a study of ontogenetic trends in primary (apical) and secondary (stem thickening) growth of plants in Arctic (Svalbard, Norway) and alpine (Krkonoše, Czechia) populations of the black crowberry (Empetrum nigrum), the dominant plant species of certain tundra communities. The environmental conditions in alpine areas are more favourable for plant growth than those in the High Arctic, where temperatures are lower, there is less precipitation and soils are shallower, among other differences. These differences were clearly reflected in significant distinctions in absolute growth rates and shrub age between the populations under study. However, we found almost no divergence in ontogenetic growth trends between the populations (based on ring width measurements made from the base to the top of plants, known as serial sectioning). In both populations, primary and secondary stem base growth decrease over the course of ontogeny whereas secondary stem top growth and basal area increment increase. No significant differences in the slope of the trends were found in either primary or secondary stem base growth. Trends of the growth ratio between basal area increment and primary growth revealed neither absolute nor relative differences between the populations. Ontogenetic trends in the shrubs analysed were surprisingly stable despite the prominently dissimilar environmental conditions. Empetrum plants have adapted to the different environments by altering their absolute growth rate only. This adaptation has probably also resulted in the different longevity of plants constituting the study populations, confirming the theory that slower-growing plants live longer. Primary growth and secondary stem base growth seem to be more basic characteristics of plant growth compared to basal area increment and secondary growth at the apex because the latter two seem to be dependent on the absolute growth rate.     

Effects of plant leachates from four boreal understorey species on soil N mineralization, and white spruce (Picea glauca) germination and seedling growth

BACKGROUND AND AIMS: Natural regeneration of white spruce (Picea glauca) after disturbance has been reported to be very poor. Here a study was made to determine whether C compounds released from understorey species growing together with white spruce could be involved in this regeneration failure, either by (1) changing soil nutrient dynamics, (2) inhibiting germination, and/or (3) delaying seedling growth. METHODS: Foliage leachates were obtained from two shrubs (Ledum palustre and Empetrum hermaphroditum) and one bryophyte (Sphagnum sp.) with high phenolic compound concentrations that have been reported to depress growth of conifers in boreal forests, and, as a comparison, one bryophyte (Hylocomium splendens) with negligible phenolic compounds. Mineral soil from a white spruce forest was amended with plant leachates to examine the effect of each species on net N mineralization. Additionally, white spruce seeds and seedlings were watered with plant leachates to determine their effects on germination and growth. KEY RESULTS: Leachates from the shrubs L. palustre and E. hermaphroditum contained high phenolic compound concentrations and dissolved organic carbon (DOC), while no detectable levels of C compounds were released from the bryophytes Sphagnum sp. or H. splendens. A decrease in net N mineralization was determined in soils amended with L. palustre or E. hermaphroditum leachates, and this effect was inversely proportional to the phenolic concentrations, DOC and leachate C/N ratio. The total percentage of white spruce germination and the growth of white spruce seedlings were similar among treatments. CONCLUSIONS: These results suggest that the shrubs L. palustre and E. hermaphroditum could negatively affect the performance of white spruce due to a decrease in soil N availability, but not by direct effects on plant physiology.