ABSTRACT
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 Tegoska 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.
ABSTRACT
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.
