Variation in leaf traits of an Apennine grass Sesleria nitida along a narrow altitudinal gradient at Mount Terminillo (Italy)

The forecasted increase of air temperature could determine the reduction of alpine habitat and loss of many European high-mountain plants (Pauli et al., 2012. Science 336: 353-355) and an increasing number of studies show altitudinal range shifts for mountain species for alpine ecosystems. The current rate of global warming might be too rapid for natural migration to successfully deliver species to suitable habitats. Thus, knowledge on alpine species response to temperature changes can provide insights into our standing how these plants are responding to current and future warming (Shen et al., 2009. J Plant Ecol 2: 207-216). The genus Sesleria Scop. constitutes a complex group of similar and closely related taxa distributed mostly throughout Europe (Kuzmanovi et al., 2009. Bot Serb 33: 51-67). The species Sesleria nitida Ten. grows in Italy from 600 to 2000 m a.s.l. in the central and southern Apennine (Pignatti, 1982. Flora d’Italia. Edagricole). The aim of this research was to analyze morphological and physiological traits of S. nitida growing at different altitudes at Mount Terminillo (42 28’ 28” N, 13 00’ 24” E, Italy) on calcareous rocky slopes. We addressed the question if altitudinal variations in morphological and physiological traits could be indicative of their future adaptive potential to global warming. The results underline a significant variation among morphological and anatomical traits with an increased specific leaf mass area (LMA) and leaf thickness (Lt) in response to variations in microsite from the low altitude (L, 1100 m a.s.l.) toward the top (T, 1895 m a.s.l.). The reduced leaf area and the increased Lt associated to the largest lateral xilem vessels size in T than in L favor the hydraulic conductivity. A higher hydraulic conductivity is adaptive in habitats with high irradiance as it allows water transport rate from roots to the foliage for photosynthesis (Barigah et al., 2006. Tree Physiol 26: 1505-15 16; Nardini et al., 2012. Tree Physiol 32: 1434-1441). The photosynthetic rates (Pn) are 18% higher in L than in T where the temperature is, on an average, 3C lower than in L, associated to a stronger wind and high irradiance causing a condition of physiological aridity. Leaf respiration shows an opposite Pn trend with 28% higher rates in T than in L. An important role to the strategy of S. nitida to the natural habitat is leaf rolling which increases in altitude. Leaf rolling reduces leaf transpiration through changes in both stomatal conductance and leaf area. The plasticity index sensu Valladares (0.27, mean value of morphological, anatomical and physiological traits of the two monitored populations) is higher compared to other mountain species (Carpenter et al. 1980. Can J Bot 59: 1393-1396) thus, reflecting S. nitida capability to maintain function under diverse environmental conditions. The results on the whole suggest that S. nitida may sustain the air temperature increasing by shifting toward higher elevation, accordin to Jump and Penuelas 2005 (Ecology Letters 8: 1010-1020) and Gratani et al. 2012 (Photosynthetica 50: 15-23) for other species.