We studied the selected anatomical and physiological characteristics of the plant (Saxifraga hostii), which thrives in various microclimate conditions at the altitude gradient in the western Julian Alps in the Kobariski Stol. Alpine plant Saxifraga hostii Tausch subsp. hostii was studied at two altitudes (montane, 1095 m a.s.l.; subalpine, 1504 m a.s.l.). Plants were grown under two different UV exposures, ambient UV (UV) and reduced UV (UV-) radiation and temperature was monitored at both altitudes. Physiological measurements, and morphological analyses were carried out during the growing season, between June and September 2016. High photochemical efficiency under both UV regimes and altitudes was observed, showing a well acclimated plant. The higher transpiration under ambient UV-B at the subalpine altitude compared to the montane altitude could be due to a synergistic effect of UV and other climatic factors such as temperature and relative humidity. Most leaf anatomical characteristics failed to respond to differences in UV dose or altitude. Saxifraga hostii has at the subalpine altitude on both sides of the leaf smaller stomatal length and higher stomatal density compared to the montane altitude, where the stomatal length is bigger and the stomatal density is lower. This study proves that UV exposure can contribute to the induction of tolerance of other environmental stresses at the subalpine altitude. UV radiation interacts with temperature regime, as well as with other environmental factors, and this evokes diverse plant responses, which together contribute to the adaptation and acclimation of Saxifraga hostii to the alpine environment. These days field studys are rare, therefore is a need for further multifactorial UV-B exposure studies whereby plants are simultaneously or sequentially exposed to UV-B and other environmental variables, and plant responses are measured at all organisation levels.
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