Theoretical and applied knowledge of plant water relations to minimise water needs of green roofs

The implementation of green roof systems in drought prone areas is an urgent need in the frame of nature-based solutions for adaptation of urban areas to ongoing climate changes. However, installation of green roofs in hot and dry regions is difficult because of challenges associated with plant survival and sustainable water use in irrigation systems. Here, we present a brief overview of basic concepts of soil-plant water relations as based on principles of irreversible thermodynamics. We highlight how the definition of critical substrate- and species-specific water potential (free energy of water per unit molar volume) levels, with specific reference to the turgor loss point, can inform: (i) the production of substrates with high amounts of water available to plants, (ii) the selection and introduction in green roofs of plant species with higher drought tolerance, and (iii) the design of deficit irrigation systems based on monitoring of substrate water potential targeted at minimising water supply while maximising some of the plant- and substrate-specific technical performances.