Surface morphology, leaf and cuticle thickness of four dwarf shrubs from a sub-Arctic heath following long-term exposure to enhanced levels of UV-B

In 1991 a field experiment was established in subarctic heathland at Abisko (68°35'N, 18°82'E), northern Sweden, to investigate the effects of enhanced UV-B (280–315 nm) radiation, simulating 15% ozone depletion, on plants in their natural environment. Leaves of the four dominant dwarf shrubs, the deciduous Vaccinium myrtillus L. and V. uliginosum L. and the evergreen V. vitis-idaea L. and Empetrum hermaphroditum Hagerup were examined after 7 years of UV-B treatment. SEM and ESEM were used to visualize surface features and to determine trichome density. Multiphoton laser scanning microscopy showed that UV-B absorbing compounds were localized in the trichomes of all species. Trichomes varied in size, number and distribution between the species. Enhanced UV-B reduced adaxial trichome density significantly (by approximately 25%) in only one species, V. uliginosum . This effect could be of importance for the UV-B absorbing potential of the adaxial epidermis of V. uliginosum . Epicuticular wax structures were found only on the abaxial surface of V. uliginosum and were unaffected by enhanced UV-B. The cuticular surfaces of all other species were smooth and featureless. Leaf thickness, adaxial and abaxial cuticle thickness varied between the species although there was no apparent effect of enhanced UV-B. It is concluded that long-term enhancement of UV-B has an effect on adaxial trichome density in V. uliginosum , but that there is no general effect on leaf morphology of the other species.     

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.     

Contrasting strategies for UV-B screening in sub-Arctic dwarf shrubs

The content and distribution of UV-absorbing phenolic compounds was investigated in leaves of three species of Vaccinium co-existing at a site in north Sweden. Vaccinium myrtillus L., Vaccinium vitis-idaea L., and Vaccinium uliginosum L. exhibit markedly different strategies, in terms of localization and content of leaf phenolics and in their responses to UV-B enhancement. Plants were exposed to either ambient radiation or to enhancement of UV-B corresponding to 15% (clear sky) depletion of stratospheric ozone for approximately 10 years prior to commencement of this study. Vaccinium myrtillus contained the highest concentration of methanol-extractable UV-B-absorbing compounds, which was elevated in plants exposed to enhanced UV-B. Fluorescence and confocal laser scanning microscopy showed that these compounds were distributed throughout the leaf, and were particularly concentrated in chlorophyll-containing cells. In V. vitis-idaea, most phenolic compounds were cell wall-bound and concentrated in the walls of the epidermis; this pool increased in response to UV-B enhancement. It is suggested that these two plants represent extreme forms of two divergent strategies for UV-B screening, the different responses possibly being related to leaf longevity in the two species. The response of V. uliginosum was intermediate between the other two, with high concentrations of cell wall-bound phenolics in the epidermis but with this pool decreasing, and the methanol-soluble pool tending to increase, after exposure to enhanced UV-B. One explanation for this response is that this plant is deciduous, like V. myrtillus, but has leaves that are structurally similar to those of V. vitis-idaea.     

Time to chill: effects of simulated global change on leaf ice nucleation temperatures of subarctic vegetation

We investigated the effects of long-term (7-yr) in situ CO(2) enrichment (600 μmol/mol) and increased exposure to UV-B radiation, the latter an important component of global change at high latitudes, on the ice nucleation temperatures of leaves of several evergreen and deciduous woody ericaceous shrubs in the subarctic (68° N). Three (Vaccinium uliginosum, V. vitis-idaea, and Empetrum hermaphroditum) of the four species of shrubs studied showed significantly higher ice nucleation temperatures throughout the 1999 growing season in response to CO(2) enrichment and increased exposure to UV-B radiation relative to the controls. The same species also showed a strong interactive effect when both treatments were applied together. In all cases, leaves cooled to below their ice nucleation temperatures failed to survive the damage resulting from intracellular ice formation. Our results strongly suggest that future global change on a decadal time scale (atmospheric CO(2) increases and polar stratospheric O(3) destruction) will lead to increased foliage damage of subarctic vegetation by severe late spring or early autumnal frosting events. Indeed, in support of our experimental findings, there is now some evidence that increases in atmospheric CO(2) concentration over the past three to four decades may already have acted in this manner on high-elevation arboreal plants in the Swedish Scandes. The implications for vegetation modeling in a future "greenhouse" world and palaeoclimate estimates from high-latitude plant fossils dating to the high-CO(2) environment of the Mesozoic are discussed.     

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.     

Vegetation shift from deciduous to evergreen dwarf shrubs in response to selective herbivory offsets carbon losses: evidence from 19 years of warming and simulated herbivory in the subarctic tundra

Selective herbivory of palatable plant species provides a competitive advantage for unpalatable plant species, which often have slow growth rates and produce slowly decomposable litter. We hypothesized that through a shift in the vegetation community from palatable, deciduous dwarf shrubs to unpalatable, evergreen dwarf shrubs, selective herbivory may counteract the increased shrub abundance that is otherwise found in tundra ecosystems, in turn interacting with the responses of ecosystem carbon (C) stocks and CO₂ balance to climatic warming. We tested this hypothesis in a 19‐year field experiment with factorial treatments of warming and simulated herbivory on the dominant deciduous dwarf shrub Vaccinium myrtillus. Warming was associated with a significantly increased vegetation abundance, with the strongest effect on deciduous dwarf shrubs, resulting in greater rates of both gross ecosystem production (GEP) and ecosystem respiration (ER) as well as increased C stocks. Simulated herbivory increased the abundance of evergreen dwarf shrubs, most importantly Empetrum nigrum ssp. hermaphroditum, which led to a recent shift in the dominant vegetation from deciduous to evergreen dwarf shrubs. Simulated herbivory caused no effect on GEP and ER or the total ecosystem C stocks, indicating that the vegetation shift counteracted the herbivore‐induced C loss from the system. A larger proportion of the total ecosystem C stock was found aboveground, rather than belowground, in plots treated with simulated herbivory. We conclude that by providing a competitive advantage to unpalatable plant species with slow growth rates and long life spans, selective herbivory may promote aboveground C stocks in a warming tundra ecosystem and, through this mechanism, counteract C losses that result from plant biomass consumption.     

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.     

Responses of alpine shrubs to simulated environmental change during three years in the mid-latitude mountain, northern Japan

Effects of artificial warming on phenology, individual leaf traits, vegetative growth, and reproduction of five alpine species (two deciduous and three evergreen shrubs) were investigated during three years in the mid-latitude alpine, northern Japan. Eleven open-top chambers (OTCs) were set up on a fellfield (1680 m a. s. l.) in the Taisetsu Mountains by which air temperature at plant height was increased by ca 2°C. Vaccinium uliginosum (deciduous shrub) showed earlier leaf emergence in every season and earlier flowering only in the first season in the OTCs. By contrast, acceleration of leaf emergence in the OTCs was not clear for other species, i.e. Arctous alpinus (deciduous shrub). Ledum palustre. V. vitis-idaea , and Empetrum nigrum (evergreen shrub). Both deciduous species showed longer leaf life-span in the OTCs every season. All evergreen species had higher leaf survival rates in the OTCs. indicating extension of leaf life-span. Leaf nitrogen concentration and leaf mass per unit leaf area (mg cm ⁻²) generally tended to decrease in the OTCs. Relationships between the individual leaf traits and cumulative air temperature during the leaf developing period were not clear. Total leaf production during the three seasons increased in the OTCs in A. alpinus. L. palustre. V. vitis-idaea , and E. nigrum. All evergreen shrubs showed larger shoot growth in the OTCs but both deciduous shrubs did not show significant changes. In contrast to the vegetative growth, deciduous shrubs produced more flowers in the OTCs. Fruit production was not influenced by the OTCs for all species. The extension of photosynthetic period in the OTCs may contribute to the larger vegetative growth or flower production.     

The impacts of UV-B radiation on the regeneration of a sub-arctic heath community

The effects of ultraviolet-B radiation on regeneration after disturbance of a natural sub-arctic heathland have been investigated. Areas of pristine dwarf shrub heath were denuded of all above ground biomass in 1992 and exposed to enhanced UV-B (simulating a 15% depletion of the ozone layer). The resulting regenerated stem and leaf growth parameters were measured after four years on three dwarf shrubs, Vaccinium myrtillus, V. uliginosum and V. vitis-idaea and the grass Calamagrostis lapponica; leaves of the three dwarf shrubs were also analysed for UV-absorbing compounds and carbohydrates. Regeneration irrespective of treatment was slow, with Empetrum hermaphroditum failing to regenerate at all. Vaccinium myrtillus showed the most rapid regeneration attaining much of its original biomass in four years. There was a significant interaction between UV-B and year of regeneration in V. myrtillus; annual stem length increment showed an initial stimulation of 75% under enhanced UV-B in the first year of regeneration while a reduction of 16% was observed in the fourth year. Both V. uliginosum and V. vitis-idaea showed a reduction in annual stem length increment as regeneration progressed with a greater than 50% reduction in stem increment in the fourth year of regeneration compared to the first. Vaccinium uliginosum also showed an initial reduction in stem length increment of 40% under enhanced UV-B. None of the species were affected by enhanced UV-B in terms of total regenerated stem and leaf biomass or UV-absorbing compounds in regenerated leaf tissue. Total leaf carbohydrate and the ethanol/water soluble fraction in V. uliginosum were significantly increased by 29% and 31% respectively under enhanced UV-B. This suggests either a stimulation of photosynthesis or a reduction in sink size for photo-assimilates. Results are discussed in the context of the extremely slow regeneration of sub-arctic heath communities and the implications of contrasting UV-B effects on the regenerative ability of different species.     

The effects of UV-B radiation on European heathland species

The effects of enhanced UV-B radiation on three examples of European shrub-dominated vegetation were studied in situ. The experiments were in High Arctic Greenland, northern Sweden and Greece, and at all sites investigated the interaction of enhanced UV-B radiation (simulating a 15% reduction in the ozone layer) with artificially increased precipitation. The Swedish experiment also involved a study of the interaction between enhanced UV-B radiation and elevated CO₂ (600 ppm). These field studies were supported by an outdoor controlled environment study in the United Kingdom involving modulated enhancement of UV-B radiation in combination with elevated CO₂ (700 ppm). Effects of the treatments on plant growth, morphology, phenology and physiology were measured. The effects observed were species specific, and included both positive and negative responses to the treatments. In general the negative responses to UV-B treatments of up to three growing seasons were small, but included reductions in shoot growth and premature leaf senescence. Positive responses included a marked increase in flowering in some species and a stimulation of some photosynthetic processes. UV-B treatment enhanced the drought tolerance of Pinus pinea and Pinus halepensis by increasing leaf cuticle thickness. In general, there were few interactions between the elevated CO₂ and enhanced UV-B treatments. There was evidence to suggest that although the negative responses to the treatments were small, damage may be increasing with time in some long-lived woody perennials. There was also evidence in the third year of treatments for effects of UV-B on insect herbivory in Vaccinium species. The experiments point to the necessity for long-term field investigations to predict the likely ecological consequences of increasing UV-B radiation.     

Niche differentiation with respect to light utilization among coexisting dwarf shrubs in a subarctic woodland

Summary Canopy structure, shoot design, and photosynthetic light recruitment were used to compare four coexisting dwarf shrub species with respect to light utilization. All four species showed different shoot designs which probably result in different light interception properties. Leaves of Vaccinium uliginosum showed the highest levels of photosynthetic light saturation but in situ the shoots of this species reached their maximum photosynthetic rate at the lowest photon flux densities. No consistent differences with respect to photosynthetic light responses were found between deciduous and evergreen species. At sites dominated by one of the deciduous species (Vaccinium uliginosum or V. myrtillus), the two evergreen species studied (V. vitis-idaea and Empetrum hermaphroditum) occurred in the understory, i.e., with their leaf distribution slightly below that of the deciduous species. Sites dominated by one of the evergreen species showed less vertical differentiation in leaf distribution between species.     

Mechanisms that limit pollinator range in Ericaceae

Studies were conducted in 2001-2003 at Valdai National Park (Novgorod region) and at the Zvenigorod biological station of Moscow State University. The morphology of flowers, flowering dynamics and composition of insect visiting flowers of Ericaceae species: Andromeda polifolia, Chamaedaphne calyculata, Ledum palustre, Oxycoccus palustris, Vaccinium myrtillus, V. uliginosum, and V. vitis-idaea L. were studied. Some species of insects visiting flowers were excluded from the list of pollinators on the basis of observation on their behavior. L. palustre was visited mainly by flies where as other investigated species were visited mainly by bumblebees. In some cases bumblebees were the only visitors of the investigated plants. Mechanisms that protect flowers from flies and short-tongued solitary bees visits and ensure a best pollination by bumblebees are various among different species of Ericaceae. Efficiency of nectary protection also differs among different plant species and is defined by particularities of their habitats and flowering phenology. As far as all species of this family during the flowering are dominants in typical habitats, a competition for the pollination with species of other families in most cases is megligible. Flowering periods of V. vitis-idaea and V. myrtillus in forest ecosystems overlapped weakly. Moreover, V. myrtillus is pollinated mainly by bumblebee queens where as pollinators of V. vitis-idaea are bumblebee workers, solitary bees and horse flies. The other investigated plant species inhabit only oligotrophic peat bogs. Thery are pollinated by bumblebees but periods of flowering are not overlapped and consequently follow one after another. L. palustre and V. uliginosum flower simultaneosly but they are pollinated by different pollinators.     

Leaf habit influences nitrogen remobilization in Vaccinium species.

The effect of N supply on plant growth and leaf demography of a deciduous and an evergreen Ericaceae was studied in relation to their internal cycling of N. Mature ramets of Vaccinium myrtillus (deciduous) and Vaccinium vitis-idaea (evergreen) were established in sand culture for 1 year with an adequate supply of a balanced nutrient solution. During one growing season, the plants were given two levels of N supply enriched with 15N and eight sequential destructive harvests were taken. Recovery of unlabelled N in the new shoot was used to determine the remobilization of N from storage. Initially, growth was unaffected by N supply. After May, High N enhanced growth for both species but the nature of their growth response differed. For both species, new shoot biomass and leaf number increased but root biomass production was affected for V. myrtillus only. Whole plant biomass production was similar for both species under High N, but was greater for V. vitis-idaea under Low N. The amount of N remobilized to support new shoot growth was similar for the two species and was independent of N current supply. N was remobilized predominantly from previous year leaves for V. vitis-idaea and from previous year stems and roots for V. myrtillus. The contribution of remobilization to new shoot N was similar for the two species, but depended on N supply. Remobilization was faster in V. myrtillus, but lasted longer in V. vitis-idaea. The results are discussed in relation to species growth in N-poor environments, focusing on the extent to which species-differences in the dynamic of N remobilization and growth may explain their adaptation to constant and/or changeable N supply.     

Effects of water and mineral nutrient supply on a deciduous and an evergreen dwarf shrub: Vaccinium uliginosum L. and V. vitisidaea L.

The effects of irrigation and fertilization on nutrient content, shoot growth and photosynthetic rate of the deciduous Vaccinium uliginosum L. and the evergreen V. vitis-idaea L. were studied in a field experiment at Abisko, Swedish Lapland. V. vitis-idaea responded to fertilization with a greater increase in leaf nitrogen, phosphorus and potassium concentrations, as well as with a relatively greater change in shoot growth than V. uliginosum . Also to irrigation did V. vitis-idaea respond more strongly. Decreased leaf longevity was indicated in both irrigated and fertilized plants of V. vitis-idaea . It is concluded that no general response pattern for evergreen and deciduous plants can be expected to emerge unless one also takes other plant characteristics, and also site characteristics, into consideration.     

Ambient UV-B radiation decreases photosynthesis in high arctic Vaccinium uliginosum

An UV-B-exclusion experiment was established in high arctic Zackenberg, Northeast Greenland, to investigate the possible effects of ambient UV-B on plant performance. During almost a whole growing season, canopy gas exchange and Chl fluorescence were measured on Vaccinium uliginosum (bog blueberry). Leaf area, biomass, carbon, nitrogen and UV-B-absorbing compounds were determined from a late season harvest. Compared with the reduced UV-B treatment, the plants in ambient UV-B were found to have a higher content of UV-B-absorbing compounds, and canopy net photosynthesis was as an average 23% lower during the season. By means of the JIP-test, it was found that the potential of processing light energy through the photosynthetic machinery was slightly reduced in ambient UV-B. This indicates that not only the UV-B effects on PSII may be responsible for some of the observed reduction of photosynthesis but also the effects on other parts of the photosynthetic machinery, e.g. the Calvin cycle, might be important. The 60% reduction of the UV-B irradiance used in this study implies a higher relative change in the UV-B load than many of the supplemental experiments do, but the substantial effect on photosynthesis clearly indicates that V.   uliginosum is negatively affected by the current level of UV-B.     

Climate change – Bad news for montane forest herb layer species?

Global warming presents a threat to plant species distributed at montane or alpine altitudes if the topography does not allow upward shifts in distribution ranges. Nevertheless, the species might also benefit from increasing temperatures and secondary effects on dominant species (e.g. bark beetle outbreaks or summer drought affecting the canopy species). As a consequence, disturbance frequency in montane forests might increase and light availability for herb layer species will increase. We addressed these interactions in a common garden experiment in Central Germany at different altitudes, representing cold and moist vs. warm and dry conditions. We investigated three montane species with different life forms, including a herb (Trientalis europaea), a grass (Calamagrostis villosa) and a dwarf shrub (Vaccinium myrtillus) under three shading treatments (3%, 28% and 86% of full sunlight). We hypothesized that montane species are at a disadvantage in the lowland, with the dwarf shrub suffering more than the grass. Furthermore, we hypothesized an antagonistic interaction of increased temperature and increased light conditions. While T. europaea and V. myrtillus showed only slightly responses to low altitude conditions, C. villosa displayed a nearly fifteen fold increase in biomass production, despite higher observed herbivory levels in the lowland. We failed to show an antagonistic effect of increased temperature and increased light availability, as all study species suffered from deep shade conditions and grew best under full light conditions at both sites. In conclusion, both improved temperature and light conditions might be principally beneficial for the investigated boreal species, in particular for the grass species C. villosa.     

Compensatory growth of two clonal dwarf shrubs, Arctostaphylos uva-ursi and Vaccinium uliginosum in a heavy metal polluted environment

The effect of artificial shoot clipping on the vegetative growth and sexual reproduction of the evergreen bearberry, Arctostaphylos uva-ursi, and the deciduous bog bilberry, Vaccinium uliginosum, was studied in the vicinity of a copper-nickel smelter in SW Finland. According to the research hypothesis, heavy metal induced shoot death breaks the apical dominance in the clones growing in a polluted environment. This causes activation of dormant axillary and adventitious buds and an increase in branching on the older parts of the stem. Regrowth after shoot death was studied by clipping off all the current-year shoots from experimental branches in autumn (1994) and spring (1995). Within-clone and between-clone control branches were used to test the data.Both species displayed a considerable ability to activate dormant meristems after the damage. Regrowth of the current shoots during the next growing season (1995) was about 80% compared to the within-clone control in both species after autumn clipping. Shoot clipping in early summer was more detrimental for both species, and the regrowth of A. uva-ursi was less than that of V. uliginosum. Differences in the storage reserves and source-sink mechanisms of carbon allocation between evergreen and deciduous species probably explain their distinct response. When the removed biomass was added to the living biomass of the branches, there was overcompensation in the total dry weight of A. uva-ursi after autumn clipping, and the weight was almost 90% of the control after spring clipping. The total dry weight of V. uliginosum also equalled that of the control when the removed biomass was added. No berries developed on either species in the year following the autumn treatment, because clipping removed all the flower buds. Spring clipping had no effect on the sexual reproduction of A. uva-ursi, but decreased the berry production of V. uliginosum. The degree of compensatory growth of both species was only slightly affected by the distance from the smelter. It is suggested that dormant bud activation, rapid regrowth and plastic branching contribute to the resistance mechanism to heavy metals.     

Seasonal development of cold stress resistance in several plant species at a coastal and a continental location in North Norway

Summary Samples of 17 plant species (one herb, dwarf shrubs and trees) were collected monthly throughout the winter 1976/77. Samples were frozen down to selected temperatures and hardiness was estimated by visual observations of oxidative browning and bud break. In most species hardiness rapidly increased from September to November and dehardening started in February–March. In six species (Betula pubescens Ehrh., Picea abies (L.) Karst., Salix caprea L., Sorbus aucuparia L., Vaccinium myrtillus L., V. vitis-idaea L.) hardening developed faster at the continental than at the coastal location. Differences in maximum hardiness between sampling locations were generally small and there were no real differences in dehardening of the plants between the locations. Both twigs and buds of Salix pentandra L. and Populus tremula L. survived liquid nitrogen in January–February.     

Decreased frost hardiness of Vaccinium vitis-idaea in reponse to UV-A radiation

The aim of this study was to investigate plant frost hardiness responses to ultraviolet (UV) radiation, since the few results reported are largely contradictory. It was hypothesized that functional adaptation of life forms could explain these contradictions. Dwarf shrubs and tree seedlings, representing both evergreen and deciduous forms, were tested (Vaccinium vitis-idaea, Vaccinium myrtillus, Pinus sylvestris, Betula pubescens and its red form f. rubra). The research was performed in Sodankyl?, Northern Finland (67°N), with enhanced UV-B- and UV-A-radiation treatments between 2002 and 2009. Plant frost hardiness was determined using the freeze-induced electrolyte leakage method in early autumn, during the onset of the frost hardening process. Additional physiological variables (malondialdehyde, glutathione, total phenols, C and N contents) were analyzed in V. vitis-idaea to explain the possible responses. These variables did not respond significantly to UV-radiation treatments, but explained the frost hardiness well (r2 = 0.678). The main finding was that frost hardiness decreased in the evergreen shrub V. vitis-idaea, particularly with enhanced UV-A radiation. No significant responses were observed with the other plants. Therefore, this study does not support the idea that enhanced UV radiation could increase plant frost hardiness.     

Growth and reproduction of the alpine grasshopper <Emphasis Type="Italic">Miramella alpina</Emphasis> feeding on CO<Subscript>2</Subscript>-enriched dwarf shrubs at treeline

The consequences for plant-insect interactions of atmospheric changes in alpine ecosystems are not well understood. Here, we tested the effects of elevated CO₂ on leaf quality in two dwarf shrub species (Vaccinium myrtillus and V. uliginosum) and the response of the alpine grasshopper (Miramella alpina) feeding on these plants in a field experiment at the alpine treeline (2,180 m a.s.l.) in Davos, Switzerland. Relative growth rates (RGR) of M. alpina nymphs were lower when they were feeding on V. myrtillus compared to V. uliginosum, and were affected by elevated CO₂ depending on plant species and nymph developmental stage. Changes in RGR correlated with CO₂-induced changes in leaf water, nitrogen, and starch concentrations. Elevated CO₂ resulted in reduced female adult weight irrespective of plant species, and prolonged development time on V. uliginosum only, but there were no significant differences in nymphal mortality. Newly molted adults of M. alpina produced lighter eggs and less secretion (serving as egg protection) under elevated CO₂. When grasshoppers had a choice among four different plant species grown either under ambient or elevated CO₂, V. myrtillus and V. uliginosum consumption increased under elevated CO₂ in females while it decreased in males compared to ambient CO₂-grown leaves. Our findings suggest that rising atmospheric CO₂ distinctly affects leaf chemistry in two important dwarf shrub species at the alpine treeline, leading to changes in feeding behavior, growth, and reproduction of the most important insect herbivore in this system. Changes in plant-grasshopper interactions might have significant long-term impacts on herbivore pressure, community dynamics and ecosystem stability in the alpine treeline ecotone.