Dottorato in BIOLOGIA AMBIENTALE ED EVOLUZIONISTICA

Titolo della tesi: Intraspecific variability of multiple Mediterranean plant functional traits in response to aridity

Summer Drought is a recurring event in the Mediterranean region, although its occurrence is undergoing an increase both in duration and intensity due to Climate Change. Plants mainly perceive aridity through water stress and heath intensity, which drive in them both physiological and morphological responses. The former allow for quick responses to temporary variations, while the latter allow each individual to adopt an optimized form to resist its local environment. This intraspecific variation (ITV) is reflected by plant functional traits, and with this PhD thesis we attempt to address how local climate heterogeneity can affect drought-related trait variability, ultimately influencing drought resistance. This project was conduced on three neighbouring populations from central Italy, chosen along an aridity gradient to maximize climate heterogeneity while minimizing distances. Several co-occurring Mediterranean plant species were gradually analysed to determine whether: 1) they would present significant ITV between populations in situ, 2) they would present significant ITV between provenances among seedlings grown in a Common Garden, and 3) seedlings grown in Common Garden would be differently affected by an experimentally induced water stress. These objectives were designed to gradually overcome the limitations of each study, ultimately trying to respond to the question “can local climatic heterogeneity shape plants responses to drought?”. The first layer of this project served to determine the presence of significant between-populations ITV, which was observed in a multivariate space of multiple drought-related plant functional traits. The main limitation of this study was that it wouldn’t allow to distinguish between plasticity and adaptations, the two main possible sources of variations between groups. The second layer served to overcome this limitation by introducing seedlings grown in a common environment, and allowed us to determine which species were inheriting locally adapted functional traits and which species were simply relying on phenotypic plasticity to respond to local environments. We also took advantage of this study to address the issue of local homogeneity, the assumption that close-by groups would share similar ecological characteristics, arguing that environmental heterogeneity can drive adaptation at the scale of tens of Kilometres. The last layer of this project was designed to determine whether the local adaptations we described would induce different physiological responses to drought conditions. For this, we subjected the same seedlings of two species grown in common garden to an experiment of induced water stress, and we observed significantly different responses between plants hailing from wet and arid provenances for one species. Given these results, we conclude that climate heterogeneity can induce significant ITV in Mediterranean plants at local scale, significantly affecting drought resistance in some instances.