UV radiation and temperature effects on functional traits in Helianthemum nummularium subsp. grandiflorum at the alpine and montane site in the Slovenian Alps

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, wherespecific characteristics of plant species should not be overlooked.