Cohabiting native Fraxinus ornus and alien Ailanthus altissima differ in their ecophysiological responses and functional traits.
Fraxinus ornus cohabits with the alien species Ailanthus altissima, which is invasive throughout Europe and North America. This work studied ecophysiological response of two cohabiting species and their leaf and bark traits to contribute to understanding A. altissima invasiveness. We compared the radiation-use and water-use efficiency following 6 months of good water supply as opposed to a pronounced water shortage in two cohabiting species. Leaf anatomical properties were studied, and their differences in leaf and bark biochemical and optical properties were examined. The two species differed significantly in leaf morphology, but less so for leaf biochemistry. This latter differed more in comparison from two precipitation levels within the same species. Compared to F. ornus, the A. altissima leaves were thicker, with thicker epidermal and palisade layers, and less numerous, but larger, stomata. A. altissima had higher effective photochemical efficiency and maintained a more favourable water potential despite higher stomatal conductance with high precipitation, meanwhile there were no significant differences of ecophysiological responses in low precipitation. There were only small differences between the two species for the leaf optical properties, while they differed significantly for the bark optical properties. We show that pigments have an important role in defining bark reflectance, and that differences in bark spectral signatures provide a basis for the distinction between these two species for remote sensing.