Physiological responses of five Holm oak (Quercus ilex L.) ecotypes to seasonal climatic factor variations

In the Mediterranean type ecosystems air temperature is a very important environmental driver for photosynthetic capacity due to the interaction with environmental stressors. Extreme temperature values may significantly affect Mediterranean plant productivity and distribution. Quercus ilex L. is a deep-rooted evergreen species, widely distributed in the Mediterranean Basin. It seems to be limited in its southern range by summer drought and in altitude by climatic factors associated with low temperatures. The physiological adaptability of Q. ilex to high temperature is very important for its future persistence in the distribution area, taking also into consideration the forecasted increase of climate change-based aridity in the Mediterranean Basin. The adaptive response to temperature depend also on the intra-specific variations due to the presence of ecotypes in the Q. ilex population (i.e. ecotypic variation). Nevertheless, few studies have been carried out to compare physiological traits of ecotypes coming from different climatic conditions and growing in the same environment. Our goal was to analyse seasonal differences in the temperature response of five Q. ilex ecotypes from different Italian geographical areas (north to south gradient) in order to test if ecotypes maintained their specific physiological responses when grew all in the same environmental conditions and to evaluate which was the most adapted to global change among them. The study was carried out on 3-year-old saplings germinated from acorns collected in five sites from the north to the south of Italy and grown under the same climatic conditions. Measurements of gas exchange, biochemistry and chlorophyll fluorescence were carried out during wintertime, springtime and summertime to analyse the ecotypic responses to seasonal air temperature variations. Moreover, a net assimilation – stomatal conductance model was applied to ecotypes in order to analyse net assimilation rates in relation to their site of provenance. The results showed different ecotypic responses that reflected the climate of the native sites, particularly under sub-optimal temperature conditions. The ecotypes coming from the northernmost and the southernmost limits were the most sensitive to temperature variations. Our results give new insights regarding the shift of Q. ilex distribution throughout Italy with ecotypes more adapted to climate change defining new boundaries.