UV radiation affects the biochemical, physiological and morphological responses of plants. The effect is most pronounced at high altitude, such as alpine regions, and low latitude environments. The effect of UV radiation is impacted by different environmental conditions including temperature. We examined the response of the alpine plant Saxifraga hostii Tausch subsp. hostii growing at two altitudes (montane, 1100 m a.s.l. and alpine, 1500 m a.s.l.) in the Slovenian Alps. Selected ecophysiological, anatomical and pigment analyses along with measurements of the leaf optical properties were carried out during the growing season from July to September. Plants were grown under two different UV levels, near-ambient UV (UV) and reduced UV (UV-) radiation, and temperature conditions were monitored at both altitudes. Saxifraga hostii exhibited high photochemical efficiency of photosystem II and stomatal conductance under near-ambient UV radiation in August, which indicates that it is a well-acclimated plant. In September, photochemical efficiency was higher under reduced UV at the alpine altitude which together with a lower photosynthetic pigment content indicate delayed senescence for plants growing under reduced UV. Most leaf tissue thicknesses were not affected by UV radiation and altitude difference. There was a trend of increased stomatal density and reduced stomatal length on both leaf surfaces under near-ambient UV in August. However, there was no effect of UV attenuation or location at the alpine or montane site on the content of UV-B absorbing compounds, which implies the plant's tolerance of UV-B radiation. Saxifraga hostii leaves showed high absorption in the UV spectrum at higher altitudes, as shown by their optical properties. This study shows that Saxifraga hostii is well-acclimated to ambient UV radiation and to the environmental conditions at both altitudes. The effect of UV radiation is impacted by site conditions and this produces diverse plant responses, which contribute to the specific functional traits of Saxifraga hostii in the high-altitude environment.

Alpine plants are exposed to demanding environmental conditions, such as high ultraviolet (UV) and photosynthetic radiation, extreme temperatures, drought, and nutrient deficiencies. Alpine plants adapt and acclimate to harsh conditions, developing several strategies, including biochemical, physiological, and optical responses. However, alpine plants’ survival strategies are hardly researched due to time-consuming and complex experimental conditions, which are supported by scarce studies. Our study focused on the functional traits of the alpine plant Alchemilla monticola Opiz (hairy lady’s mantle) growing at two different altitudes (1500, 2000 m a.s.l.) and two different UV exposures per altitude. Near-ambient (UV) and reduced (UV-) UV radiations were provided by using two sorts of UV absorbing filters; temperatures were monitored hourly. The experimental plots were located at Tegoška Gora, Karavanke, Slovenia. Functional traits: physiological, biochemical, and optical characteristics were recorded three times during the growing season. A. monticola showed high maximum photochemical efficiency at both altitudes throughout the season, which confirms good adaptation and acclimatization of the plant. Furthermore, significantly higher maximum photochemical efficiency at the subalpine altitude coincided with significantly higher UV absorbing compounds (UV AC) contents at the subalpine compared to the montane altitude in August. A. monticola manifested high UV AC contents throughout the season, with significantly increased synthesis of UV AC contents in the subalpine conditions in August and September. The stomatal conductance rate increased with altitude and was correlated mostly to a lower temperature. A. monticola leaves did not transmit any UV spectrum, which corresponded to high total UV AC contents. The leaf transmittance of the photosynthetic spectrum increased at the subalpine altitude, while the transmittance of the green and yellow spectra increased under the reduced UV radiation in the autumn. A. monticola’s high photosynthetic spectrum transmittance at the subalpine altitude in the autumn might therefore be due to subalpine harsh environmental conditions, as well as plant ontogenetical phase.

This paper reports a study of the strategies in Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.) for coping with enhanced UV-B radiation. Trees, as plants in general, possess diverse systems which respond to UV-B radiation. Changes in physiology, biochemistry and morphology have been observed in trees under enhanced UV-B radiation. The efficiency of trees’ UV-B protective systems depends on plant characteristics and state of development as well as can be correlated with the UV-B dose and the environmental conditions. The two tree species were exposed outdoors to enhanced UV-B simulating 17% ozone depletion for three years during which time, selected parameters were monitored. Selected physiological parameters were monitored three times a year on beech leaves and three needle age classes of spruce. Spruce and beech exhibited great variability in the amounts of chlorophyll, methanol-soluble UV-B and UV-A absorbing compounds, and optimum quantum yield of photosystem II. The effects of UV-B radiation also varied with needle and leaf development stage and interaction with environmental conditions. Enhanced UV-B radiation triggered responses in both trees and a reduced negative effect of UV-B radiation on spruce photochemical efficiency was observed during prolonged drought. The results show high UV-B tolerance of both tree species and indicate the complexity of plant response to UV-B, involving multilevel interactions with environmental factors and thus emphasizes the necessity of long-term investigations on trees in a natural ecosystem.

Trees as a perennial growth form require time to evolve the complex response to enhanced ultraviolet-B radiation (UV-B), and this might lead to slow but important changes in forest ecosystem structure and function. Long-term outdoor experiments on trees however are few in number. The available published results suggest that broadleaf and conifer trees may show different response strategies to enhanced UV-Bradiation. The long-term outdoor experiments indicate species- and season-specific differential responses in tree secondary metabolism, photosynthesis, water relations, and growth and development.

Alpine plants have evolved strategies to survive harsh conditions, which include high UV and visible radiation, extreme temperatures, dryness and lack of nutrients. Survival strategies include biochemical, physiological and morphological responses, which are scarcely studied because of the time-demanding and complex experimental conditions. We researched functional traits in the alpine plant common rockrose Helianthemum nummularium subsp. grandiflorum growing under ambient UV-B and reduced UV-B radiation at different altitudes (1600 and 2000 m a.s.l.) of mount Vogel in the Slovenian Alps. Leaf anatomy, pigments and optical properties were investigated at the beginning and at the end of the growing season. Plants showed high constitutive UV-absorbing compounds content (UV-AC) throughout the season. Most leaf thickness parameters were not altered according to UV and altitude conditions. Leaves did not transmit any UV spectrum, in agreement with high UV-AC. High photosynthetic spectrum transmittance at alpine altitudes was due to complex biochemical and anatomical responses to these conditions, rather than to UV radiation. Unchanged chlorophyll content of H. nummularium could be related to shrub life form, where leaves shade out high UV and PAR irradiance as well as contribute to lower leaf temperature. This study shows the complexity of alpine plant response, where specific characteristics of plant species should not be overlooked.