A Latitudinal Cline in Leaf Inclination of Dryas octopetala and Implications for Maximization of Whole Plant Photosynthesis

Mean leaf inclination of the arctic and alpine shrub Dryas octopetala is a function of latitude and this functional relationship is consistent with a model that maximizes photosynthesis of the total plant canopy.     

High diversity of root associated fungi in both alpine and arctic <Emphasis Type="Italic">Dryas octopetala</Emphasis>

Background  

Dryas octopetala is a widespread dwarf shrub in alpine and arctic regions that forms ectomycorrhizal (ECM) symbiotic relationships with fungi. In this study we investigated the fungal communities associated with roots of D. octopetala in alpine sites in Norway and in the High Arctic on Svalbard, where we aimed to reveal whether the fungal diversity and species composition varied across the Alpine and Arctic regions. The internal transcribed spacer (ITS) region of nuclear ribosomal DNA was used to identify the fungal communities from bulk root samples obtained from 24 plants.     

AFLP markers reveal high clonal diversity and extreme longevity in four key arctic-alpine species

We investigated clonal diversity, genet size structure and genet longevity in populations of four arctic‐alpine plants (Carex curvula, Dryas octopetala, Salix herbacea and Vaccinium uliginosum) to evaluate their persistence under past climatic oscillations and their potential resistance to future climate change. The size and number of genets were determined by an analysis of amplified fragment length polymorphisms and a standardized sampling design in several European arctic‐alpine populations, where these species are dominant in the vegetation. Genet age was estimated by dividing the size by the annual horizontal size increment from in situ growth measurements. Clonal diversity was generally high but differed among species, and the frequency distribution of genet size was strongly left‐skewed. The largest C. curvula genet had an estimated minimum age of c. 4100 years and a maximum age of c. 5000 years, although 84.8% of the genets in this species were <200 years old. The oldest genets of D. octopetala, S. herbacea and V. uliginosum were found to be at least 500, 450 and 1400 years old, respectively. These results indicate that individuals in the studied populations have survived pronounced climatic oscillations, including the Little Ice Age and the postindustrial warming. The presence of genets in all size classes and the dominance of presumably young individuals suggest repeated recruitment over time, a precondition for adaptation to changing environmental conditions. Together, persistence and continuous genet turnover may ensure maximum ecosystem resilience. Thus, our results indicate that long‐lived clonal plants in arctic‐alpine ecosystems can persist, despite considerable climatic change.     

Effects of temperature elevation on a field population of Acyrthosiphon svalbardicum (Hemiptera: Aphididae) on Spitsbergen

A manipulation experiment was carried out on a field population of the aphid Acyrthosiphon svalbardicum near Ny Ålesund, on the high arctic island of Spitsbergen, using cloches to raise temperature. An average rise in temperature of 2.8 deg. C over the summer season markedly advanced the phenology of both the host plant Dryas octopetala and the aphid. Advanced aphid phenology, with concomitant increases in reproductive output and survival, and successful completion of the life-cycle led to an eleven-fold increase in the number of overwintering eggs. Thermal budget requirements in day degrees above 0°C were calculated for key life-cycle stages of the aphid. Temperature data from Ny Ålesund over the past 23 years were used to calculate thermal budgets for the field site over the same period and these were compared with the requirements of the aphid. Each estimated thermal budget was then adjusted to simulate the effect of a +2, +4, and –2deg. C change in average temperature on aphid performance. This retrospective analysis (i) confirms that the life-cycle of A. svalbardicum is well suited to exploit higher summer temperatures, (ii) indicates that the annual success of local populations are sensitive to small changes in temperature and (iii) suggests that the aphid is living at the limits of its thermal range at Ny Ålesund based on its summer thermal budget requirements.     

Experimental warming increases herbivory by leaf‐chewing insects in an alpine plant community

Climate warming is predicted to affect species and trophic interactions worldwide, and alpine ecosystems are expected to be especially sensitive to changes. In this study, we used two ongoing climate warming (open‐top chambers) experiments at Finse, southern Norway, to examine whether warming had an effect on herbivory by leaf‐chewing insects in an alpine Dryas heath community. We recorded feeding marks on the most common vascular plant species in warmed and control plots at two experimental sites at different elevations and carried out a brief inventory of insect herbivores. Experimental warming increased herbivory on Dryas octopetala and Bistorta vivipara. Dryas octopetala also experienced increased herbivory at the lower and warmer site, indicating an overall positive effect of warming, whereas B. vivipara experienced an increased herbivory at the colder and higher site indicating a mixed effect of warming. The Lepidoptera Zygaena exulans and Sympistis nigrita were the two most common leaf‐chewing insects in the Dryas heath. Based on the observed patterns of herbivory, the insects life cycles and feeding preferences, we argue that Z. exulans is the most important herbivore on B. vivipara, and S. nigrita the most important herbivore on D. octopetala. We conclude that if the degree of insect herbivory increases in a warmer world, as suggested by this study and others, complex interactions between plants, insects, and site‐specific conditions make it hard to predict overall effects on plant communities.     

Low host specificity of root‐associated fungi at an Arctic site

In High Arctic ecosystems, plant growth and reproduction are limited by low soil moisture and nutrient availability, low soil and air temperatures, and a short growing season. Mycorrhizal associations facilitate plant nutrient acquisition and water uptake and may therefore be particularly ecologically important in nutrition‐poor and dry environments, such as parts of the Arctic. Similarly, endophytic root associates are thought to play a protective role, increasing plants' stress tolerance, and likely have an important ecosystem function. Despite the importance of these root‐associated fungi, little is known about their host specificity in the Arctic. We investigated the host specificity of root‐associated fungi in the common, widely distributed arctic plant species Bistorta vivipara, Salix polaris and Dryas octopetala in the High Arctic archipelago Svalbard. High‐throughput sequencing of the internal transcribed spacer 1 (ITS1) amplified from whole root systems generated no evidence of host specificity and no spatial autocorrelation within two 3 m × 3 m sample plots. The lack of spatial structure at small spatial scales indicates that Common Mycelial Networks (CMNs) are rare in marginal arctic environments. Moreover, no significant differences in fungal OTU richness were observed across the three plant species, although their root system characteristics (size, biomass) differed considerably. Reasons for lack of host specificity could be that association with generalist fungi may allow arctic plants to more rapidly and easily colonize newly available habitats, and it may be favourable to establish symbiotic relationships with fungi possessing different physiological attributes.     

Environmental constraints on the growth,photosynthesis and reproductive development of Dryas octopetala at a high Arctic polar semi-desert,Svalbard

Opportunities exist in high Arctic polar semidesert communities for colonisation of unvegetated ground by long-lived clonal plants such as Dryas octopetala. This can be achieved by lateral spread of vegetative ramets, or by sexual reproduction and seedling recruitment. The objectives of this study were (1) to determine whether these two means of proliferation show differential sensitivity to contrasting components of the abiotic environment (temperature, soil nutrient and water availability) and (2) to evaluate the potential for D. octopetala to respond to climate change by an increase in cover and biomass in polar semi-desert communities. Factorial environmental manipulations of growing season temperature, soil nutrient and water status were conducted over 3 years at a polar semi-desert community in Svalbard, Norway (78°56.12N, 11°50.4E) and both clonal and sexual reproductive performance, together with instantaneous net photosynthesis (P_n), were recorded during the third season (1993). D. octopetala capitalised rapidly on an amelioration in the availability of inorganic nutrients (N, P and K) by an expansion in leaf area and biomass supported by increased P_n per unit leaf weight, and by apparent luxury uptake of nutrients (particularly P). Several facets of sexual reproductive development and seed viability were markedly improved by elevated temperatures or soil nutrient availability. Thus although D. octopetala is a long-lived clonal plant, with many traits characteristic of stress resistance syndrome, it showed considerable phenotypic plasticity in response to environmental manipulations. The results support the hypothesis that clonal growth confers survival potential during unfavourable years, together with the ability to capitalise on nutrient flushes and recycle nutrients internally. Continued investment in sexual reproduction ensures that seed setting is successful during favourable years, even if these occur infrequently. Cimate warming in the high Arctic could thus result in changes in the cover, biomass and the relative significance of clonal versus sexual proliferation of D. octopetala (and thus the genetic diversity of the population) but the long-term responses will probably be constrained by lack of available nutrients.     

Experimental ecology of Dryas octopetala ecotypes

Summary Growth, survival and reproduction of adult plants from three reciprocally-transplanted populations of Dryas octopetala were followed over a seven year period, from 1979 to 1986. The two most different ecotypes, from snowbed and fellfield environments, were strongly selected against in extreme foreign environments via differential growth, survival, and reproduction. The more phenotypically-plastic ecotype from the snowbed experienced rapid, early mortality on the fellfield, prior to morphological adjustment, but no mortality in the last five years of the experiment. The less plastic fellfield ecotype showed no mortality for the first three years followed by a steady decline in numbers for the next four years. The ecotypic difference in plasticity may account for the contrasting mortality patterns. A population of plants with intermediate morphology was intermediate in fitness in extreme environments, but showed no superiority in its home site, suggesting that it is not a locally-adapted population. Natural selection maintains genetic differences between snowbed and fellfield populations in the face of gene flow. However, based on the response of intermediates, there appear to be limits to the degree to which selection can fine-tune adaptation along environmental gradients.     

Leaf carbon isotope discrimination and vegetative responses of Dryas octopetala to temperature and water manipulations in a High Arctic polar semi-desert,Svalbard

Integrative ecophysiological and vegetative responses of Dryas octopetala were measured in response to field perturbations of temperature, precipitation and their interactions in a polar semi-desert in Svalbard, Norway (79°N, 12°E). Leaf carbon isotope discrimination (), total leaf nitrogen concentration and leaf development were determined for photosynthetic leaves collected during the last week of August 1991, after one season of manipulations. Individual leaf weight and the total mass of leaf tissue were significantly lower when water was added, irrespective of temperature regime. Leaf carbon isotope discrimination and estimated long-term c _i/c _avalues (the ratio of CO₂ concentration in leaf intercellular spaces to that in the atmosphere) were significantly higher under all three field manipulation treatments, and was significantly reduced when Dryas was grown under drought conditions in a related greenhouse study. Nitrogen concentrations of plants from the field experiment were significantly lower under warmed conditions regardless of water regime. Our results indicate that changes in environmental conditions in high arctic settings will result in alterations of Dryas leaf gas exchange, as expressed by increases in carbon isotope discrimination, which may be accompanied by shifts in leaf nitrogen content and leaf biomass.     

Epidermal UV-screening of arctic and alpine plants along a latitudinal gradient in Europe

This study reports epidermal UV-transmittance in field-grown leaves of ecotypes of six species at three sites along a latitudinal UV-B gradient from Arctic Svalbard, via southern Norway to the French Alps for the years 1999–2001. Unexpectedly, Arctic populations had just as high epidermal UV-screening as alpine populations from lower latitudes. Dryas octopetala was the only species that significantly increased epidermal screening with increasing natural UV-B. Most species, however, showed clear differences in transmittance between years.Under controlled conditions in a growthroom, no ecotypic differences with respect to epidermal UV-B screening were found in Arctic and alpine ecotypes of Oxyria digyna, either in the absence or presence of UV-B radiation. Furthermore, UV-B transmittance in the absence of UV-B radiation in the growthroom was as low (5–6%) as in field-grown plants, indicating a high constitutive screening. Analysis of UV-B-absorbing phenolic compounds in O. digyna displayed no difference between the French Alps and Svalbard ecotypes, while the S. Norway ecotype contained significantly higher amounts of screening compounds. The qualitative analysis showed that the French Alps ecotype had a different composition of flavonoids compared with the two others, and that the ratio between di- and monohydroxylated flavonoids increased from south to north.     

The history of Dryas octopetala L. in eastern Fennoscandia

The information available concerning the Late-Quaternary history of Dryas octopetala L. in eastern Fennoscandia is surveyed. It is evident that Dryas has been an important component of the treeless periglacial vegetation which existed along most of the perimeter of the Weichselian glacier c. 10,000 B.P., marked by the Salpausselkä-Kuittijärvi-Tromsø-Lyngen end moraine arc. Dryas has not been as common in the archipelago of southern Finland, west of about 28°E long. Disjunctive recent localities inside the area still glaciated during the early Flandrian (Pre-boreal period) are relics of an immigration contemporaneous with the advance of light birch forests.     

Les flavonoides du Dryas octopetala

Two proanthocyanidins and seven flavonoids are present in the leaves of Dryas octopetala. They have been identified as procyanidin, propelargonidin, quercetin, kaempferol, isorhamnetin, corniculatusin, sexangularetin, limocitrin and gossypetin. Plant samples from both French and Norwegian sites were identical in their flavonoid composition.     

Molecular Diversity of nifH Genes from Bacteria Associated with High Arctic Dwarf Shrubs

Biological nitrogen fixation is the primary source of new N in terrestrial arctic ecosystems and is fundamental to the long-term productivity of arctic plant communities. Still, relatively little is known about the nitrogen-fixing microbes that inhabit the soils of many dominant vegetation types. Our objective was to determine which diazotrophs are associated with three common, woody, perennial plants in an arctic glacial lowland. Dryas integrifolia, Salix arctica, and Cassiope tetragona plants in soil were collected at Alexandra Fiord, Ellesmere Island, Canada. DNA was extracted from soil and root samples and a 383-bp fragment of the nifH gene amplified by the polymerase chain reaction. Cloned genotypes were screened for similarity by restriction fragment length polymorphism (RFLP) analysis. Nine primary RFLP phylotypes were identified and 42 representative genotypes selected for sequencing. Majority of sequences (33) were type I nitrogenases, whereas the remaining sequences belonged to the divergent, homologous, type IV group. Within the type I nitrogenases, nifH genes from posited members of the Firmicutes were most abundant, and occurred in root and soil samples from all three plant species. nifH genes from posited Pseudomonads were found to be more closely associated with C. tetragona, whereas nifH genes from putative alpha-Proteobacteria were more commonly associated with D. integrifolia and S. arctica. In addition, 12 clones likely representing a unique clade within the type I nitrogenases were identified. To our knowledge, this study is the first to report on the nifH diversity of arctic plant-associated soil microbes.     

The arctic fox Alopex lagopus in Fennoscandia: a victim of human-induced changes in interspecific competition and predation?

After a marked decline at the beginning of the 1900s, the arctic fox Alopex lagopus population in Fennoscandia has remained at a very low level. We suggest that the main cause for the population crash was winter starvation caused by (1) over-hunting of reindeer Rangifer tarandus populations, and thus reduced carcass availability in the mountains, and (2) increased interspecific competition for these carcasses because of increased invasion of red foxes Vulpes vulpes from lower altitudes. The failure of arctic fox populations to recover, despite increasing reindeer populations in the mid 1900s, can be explained by a concurrent strong increase in red fox numbers. Analyses of countywide hunting statistics from Norway 1891–1920 suggest that there actually was an increase in red fox numbers in the period of arctic fox decline, and that the increase in reindeer populations from the 1920s to the 1950s was accompanied by a new increase in red fox numbers. We conclude that restoring arctic fox populations most likely will require a substantial and lasting reduction of red fox populations.     

Vegetation responses to rapid climatic changes during the last deglaciation 13,500–8,000?years ago on southwest And?ya, arctic Norway

The late-glacial vegetation development in northern Norway in response to climate changes during the Aller?d, Younger Dryas (YD), and the transition to the Holocene is poorly known. Here we present a high-resolution record of floral and vegetation changes at lake Lusvatnet, south-west And?ya, between 13500 and 8000 cal b.p. Plant macrofossil and pollen analyses were done on the same sediment core and the proxy records follow each other very closely. The core has also been analyzed using an ITRAX XRF scanner in order to check the sediment sequence for disturbances or hiatuses. The core has a good radiocarbon-based chronology. The Saksunarvatn tephra fits very well chronostratigraphically. During both the Aller?d and the Younger Dryas time-periods arctic vegetation prevailed, dominated by Salix polaris associated with many typically arctic herbs such as Saxifraga cespitosa, Saxifraga rivularis and Oxyria digyna. Both periods were cold and dry. Between 12450 and 12250 cal b.p. during the Younger Dryas chronozone, the assemblage changed, particularly in the increased abundance of Papaver sect. Scapiflora and other high-Arctic herbs, suggesting the development of polar desert vegetation mainly as a response to increased aridity. After 11520 cal b.p. a gradually warmer and more oceanic climate initiated a succession to dwarf-shrub vegetation and the establishment of Betula woodland after 1,000 years at c. 10520 cal b.p. The overall late-glacial aridity contrasts with oceanic conditions in southern Norway and is probably related to sea-ice extent.     

Testing the potential of the dwarf shrub Dryas octopetala L. for dating in dendrogeomorphology

Dendrochronology has been applied around the world over decades to reconstruct historical geomorphological events and climatic conditions. Traditionally, this research has been conducted using trees (conifers as well as broad-leaved trees) but, in the last few decades, several shrub and dwarf shrub species have also been shown to be useful for dendrochronological purposes. This study assesses the potential of mountain avens (Dryas octopetala L.) to provide accurately dated information about past debris-flow events. The study site, the Marlt-Graben debris-fan, is located in South Tyrol (Italy). 119 shrubs from three debris-flow tracks were analyzed. The longest radius of each sample was measured and cross-dated to build two chronologies for each debris-flow track, one for each leveé. Correlations between these chronologies and precipitation and temperature data from five climate stations located in the proximity of the study site were calculated. The cross-dating procedure was complex, but a strict grouping of the samples, based on the specific leveés of the tracks, enabled the construction of mean chronologies for each of the individual slopes. Although the development of a mean chronology for the study area was unsuccessful, the cross-dated ages of the single shrubs allowed us to reconstruct debris-flow events by utilizing the minimum age method. The low climate correlations suggest that micro site conditions strongly influence the growth of this dwarf shrub. Although the results of this study suggest that Dryas octopetala may provide useful dendroecological information, additional information about its growth dynamics is required before this potential can be fully realized.     

Non-leguminous root nodules in Japan

Summary Among plants native to Japan, nodule formation is confirmed in 14 species and varieties of Alnus, 10 of Elacagnus, 2 of Myrica and 1 of Coriaria, in a number of instances for the first time. Plants of 20 foreign species, in 8 genera, which bear nodules in their native countries, were raised in the nursery in Tokyo; only species of Alnus, Myrica and Ceanothus formed nodules. No nodules were found on native plants ofDryas octopetala var.asiatica. In a trial extending over 12 years evidence was obtained that the growth ofPinus thunbergii was benefited by underplanting withMyrica rubra, a result attributed to nitrogen fixation in the root nodules of the latter species. In the attempted isolation of the endophytes from the nodules of Alnus and other non-legume Angiosperms, although actinomycetes peculiar to the host species were usually obtained from the nodules, none of the isolates induced nodules in re-inoculation tests. Also from Podocarpus nodules actinomycetal and bacterial strains were commonly isolated; re-inoculation tests with these are in progress.     

Inocybe praetervisa group – A clade of four closely related species with partly different geographical distribution ranges in Europe

Sequence data from a broad geographical region and different habitats show that the Inocybe praetervisa clade is comprised of four closely related species. These species of section Marginatae are characterized by having nodulose spores and a stipe that is abundantly pruinose only in the upper half. Inocybe praetervisa occurs in Southern Europe in mountainous mixed coniferous forests, and is not confirmed from Northern Europe. Inocybe rivularis occurs in northern boreal forests up to the lower alpine zone, associated with Betula in moist habitats, and is not confirmed from Southern Europe. Inocybe taxocystis is confirmed as a later synonym of I. favrei. The species has a wide geographical distribution range in Europe, mainly restricted to the alpine zone and moist soils, associated with Salix herbacea. Inocybe arctica is here described as a new species. It occurs in the arctic and higher alpine zones, associated with Dryas octopetala, Salix polaris, S. reticulata and S. herbacea. All species except I. arctica are shown to have an intercontinental distribution range and are confirmed from North America. Sequence data suggest the occurrence of one additional species in the alpine zone of China. A key to the species in the I. praetervisa group is provided.     

Within-population spatial variation in pollinator visitation rates, pollen limitation on seed set, and flower longevity in an alpine species

Pollen limitation through insufficient pollen deposition on stigmas caused by too infrequent pollinator visitation may influence the reproductive outcome of plants. In this study we investigated how pollinator visitation rate, the degree of pollen limitation, and flower longevity varied spatially among three sites at different altitudes within a population of the dwarf shrub Dryas octopetala L. in alpine southern Norway. Significant pollen limitation on seed set only occurred at the mid-elevation site, while seed set at the other sites appeared to be mainly resource limited, thus indicating a spatial variation in pollen limitation. There was no association between the spatial variation in the extent of pollen limitation and pollinator visitation rate to flowers. However, pollinator visitation rates were related to flower longevity of Dryas; sites with low visitation rates had long-lived flowers and vice versa. Thus, our results suggest within-population spatial co-variation between pollinator visitation rates, pollen limitation, and a developmental response to these factors, flower longevity.     

Phytochemical profiles and antioxidant potential of four Arctic vascular plants from Svalbard

Environmental stress in the Arctic region leads to damage in plant membranes as a result of oxidation processes. To withstand these stress conditions, plants are expected to produce antioxidants that differ from phenolics. Here, we investigated the chemical composition and antioxidative activities of four Arctic flowering plant species (Dryas octopetala, Carex rupestris, Silene uralensis and Deschampsia alpina.) through in vitro measurements of the free radical scavenging activities (FRS), inhibition of lipid peroxidation (ILP) and trolox equivalent antioxidant capacities (TEAC). D. octopetala exhibited the highest ILP (76.45?%) and FRS (86.58?%) activities. The TEAC values were higher than those of the Trolox vitamin E standard in all four species. Overall, the antioxidative activity was highest in D. octopetala, followed by C. rupestris, S. uralensis and D. alpina. Electrospray ionization tandem mass spectrometric (ESI–MS/MS) analysis of methanolic extracts of these plants revealed the presence of organoselenides, linear alkylbenzenesulfonates (LAS) and oligosaccharides, some of which are reported as antioxidants in the literature. Hence, it is likely that the antioxidant activities exhibited by these plants are not only related to the production of phenolics. This is the first report of the antioxidant potential of four Arctic flowering plants and the presence of selenides in D. octopetala and S. uralensis, and the production of LAS in C. rupestris. Our findings suggest that these plants can be used as nutraceutical sources of selenium and as biomarkers for environmental pollution.