Delaying drought-driven leaf cell damage may be the key trait of invasive trees ensuring their success in the Mediterranean basin

Invasive alien species (IAS) threaten the biodiversity richness of the Mediterranean basin, a drought-prone region. However, our knowledge on the adaptive strategies of IAS for facing Mediterranean drought summers is still incomplete. The aim of the present study is to compare the water relations and the critical relative water content (RWC) values leading to loss of cell rehydration capacity of two Mediterranean basin IAS (i.e., Ailanthus altissima (Mill.) Swingle and Robinia pseudoacacia L.) versus two co-occurring native species (i.e., Fraxinus ornus L. and Quercus pubescens Willd.). Study IAS showed higher values of water potential at turgor loss point and osmotic potential at full turgor, lower values of modulus of elasticity and leaf mass area but higher photosynthesis rate, even during the summer, with respect to the Mediterranean native species. These findings supported the hypothesis that IAS are characterized by a resource acquisitive strategy coupled with a safety-efficiency trade-off, compared with Mediterranean native species. However, similar leaf RWC thresholds leading to loss of cell rehydration capacity were recorded in the two groups of species. Moreover, IAS showed higher saturated water content and capacitance values compared with the co-occurring species. Overall, our results suggest that the success of Mediterranean IAS is driven by their ability to delay dehydration damage of mesophyll cells during Mediterranean summer drought, thereby supporting their distinctive high carbon assimilation rate.

Automated summary

Invasive alien species threaten biodiversity richness in the drought-prone Mediterranean basin. This study compares the water relations and critical relative water content (RWC) values of two Mediterranean invasive species (Ailanthus altissima and Robinia pseudoacacia) with two co-occurring native species (Fraxinus ornus and Quercus pubescens). The invasive species exhibited higher water potential and osmotic potential but lower elasticity and leaf mass area, while maintaining a higher photosynthesis rate. However, both invasive and native species exhibited similar leaf RWC thresholds leading to loss of cell rehydration capacity. Our findings suggest that the success of Mediterranean invasive species is driven by their ability to delay dehydration damage during summer drought, supporting their high carbon assimilation rate.