Plasticity of physiological and morphological leaf traits in two endangered Apennine plant species in response to different altitudes

One of the predicted consequences of global climate change is the movement of plant species to higher elevations and latitudes as the climate to which they are adapted is displaced (1). A drastic decrease of the distribution area or even extinction of plant species can be the consequence of migration processes towards higher altitudes. Populations may persist in their current areas and withstand environmental changes if they have adaptive capacity (2). Recent studies indicate substantial adaptive potential as reflected by high heritability estimates for traits likely to be selected (3). Nevertheless, there is little information on the adaptive potential in environments that are particularly threatened by climate change such as high altitude mountain areas. The aim of this research was to analyze leaf morphological and physiological traits plasticity of two populations of Crepys pygmaea L. subsp. pygmaea and Isatis apennina Ten. ex Grande growing at different altitudes on the Gran Sasso Massif. C. pygmaea and I. apennina are two perennial rhizomatous species distributed in South Europe and included in the Red List of the Italian Flora, as low risk (LR) species for Abruzzo (4) where they grow on slopes with unstable limestone screes. We addressed the question whether altitudinal variations in their morphological and physiological traits could be indicative of their future adaptive potential to survive to global warming. Our results underline significant differences in morphological and physiological traits of C. pygmaea and I. apennina growing at different altitudes on the Gran Sasso Massif, at both population and species level. At population level, leaf mass area (LMA) is significantly lower for both C. pygmaea and I. apennina populations growing at the highest altitude (2,310 m and 2,350 m, respectively) than for the populations growing at the lowest altitude (2,250 m and 2,310 m, respectively). Leaf tissue density (LTD) has the same LMA trend providing a protective function through leaf transpiration limitation thus favouring the efficiency of water for photosynthesis. At the species level, our results underline that C. pygmaea has a significantly higher plasticity index (PI) of both physiological and morphological leaf traits than I. apennina. Moreover, the populations of both the species growing at the lowest altitude have a significantly higher PI than the populations growing at the higher altitude underlining their potential of moving up in response to the hypothesised air temperature increasing. The results, on the whole, underline that global warming could drive C. pygmaea and I. apennina to higher altitudes in the Gran Sasso Massif, with C. pygmaea being favored as it has the higher PI. Further researches, including long-term monitoring are needed to establish the competitive capacity of C. pygmaea and I. apennina with other species from the same area which might migrate from the lowest to the highest altitudes on the Gran Sasso Massif.