Local adaptation in two Apennine plant species along a narrow altitudinal gradient

A recent bioclimatic envelope study on 1,350 European plants underlines that species from mountain areas might be disproportionably sensitive to climate change, and southern mountain regions are predicted to experience particularly severe species losses (Lenoir et al. 2010 J. Veg. Sci. 21: 949964). We analysed morphological and physiological traits of Crepys pygmaea L. subsp. pygmaea and Isatis apennina Ten. ex Grande growing at different altitudes (2,250, 2,310 and 2,350 m a.s.l.) on the Gran Sasso Massif (Italy) and included in the Red List of the Italian Flora as low risk (LR) species for Abruzzo. At population level our results underline that leaf mass area (LMA) is 14% lower for C. pygmaea and I. apennina populations growing at the highest altitude than those at the lowest one. Leaf tissue density (LTD) has the same LMA trend decreasing by 22% from the highest to the lowest altitude. LMA can be considered an index of the construction cost of the protective structures per unit of leaf area and is associated to carbon assimilation. Thus, the lowest LMA and LTD at the highest altitude may be justified by the highest photosynthetic rates (PN) than those at the lowest altitude as a result of a low internal resistance to CO2 transfer. Both C. pygmaea and I. apennina have the highest PN in July, when leaves are fully expanded, decreasing by 17% in C. pygmaea and 30% in I. apennina, respectively, in August during flowering, and by 50 and 38%, respectively, in September at the beginning of the senescence phase. One of the predicted consequences of global change is the movement of plants to higher elevations and latitudes as the climate to which they are adapted is displaced (Jump and Peuelas, 2005. Ecol. Lett. 8: 1010-1020). Phenotypic plasticity is likely to play a crucial role in allowing plant species to persist in their environments (Vitasse et al., 2010 Funct. Ecol. 24: 1211- 1218) buffering the effects of climatic change (Theurillat and Guisan, 2001 Climatic Change 50: 77-109). C. pygmaea and I. apennina are able to respond to environmental changes along the narrow altitudinal gradient through a high morphological (PIm) and physiological (PIp) phenotypic plasticity index. In particular, PIm and PIp are 0.35 and 0.50, respectively in C. pygmaea and 0.30 and 0.38, respectively in I. apennina. The high phenotypic plasticity index underlines the potential of the two wild populations at the lowest altitude to move up in response to the hypothesised air temperature increase. Global warming could drive C. pygmaea and I. apennina to higher altitudes in the Gran Sasso Massif, C. pygmaea being favored by the highest PIm and PIp. Considering that mountain ecosystems are centers of important areas for biodiversity conservation (Nogues-Bravo et al., 2007 Global Environ. Chang. 17: 420-428) knowledge of life history traits of threatened species is important to assess their response to global warming, in particular, when wild populations number and size are small (Gratani et al., 2011 Photosynthetica 49: 65-74).