Bioreceptivity of Living Walls: Interaction between Building Materials and Substrates, and Effect on Plant Growth

Bringing nature into urban areas is largely recognized as one of the multiple benefits of green walls. Among the existing types of living walls, those made from durable building materials have a longer lifespan and require less maintenance than many typical green wall systems. In that context, there is a need to study the bioreceptivity of materials, i.e., their ability to host living organisms. This paper presents a novel method to study the bio-receptivity of materials, by enhancing the biological and physicochemical exchanges in different mixtures of crushed materials and substrates, and by measuring their effect on plant growth. For this experiment, we crushed and sieved four different building materials (3 types of concretes and 1 brick) to increase their contact surface. We then mixed them with substrate with or without compost additions. The mixtures were used as growing media for the cultivation of two wild mural plant species in a glasshouse. Plant growth and the physicochemical evolution of the mixtures were monitored for one year. The study shows the physical and chemical differences between the building materials, their interactions with substrate composition, and their effect on plant growth. Two main results appeared: (i) high pH (>8) was the major constraint against plant growth (ii) compost addi-tions significantly compensated for adverse characteristics of the materials. Assuming that higher plant growth is associated with better bioreceptivity, this experiment introduces a quantitative method that could contribute to the evaluation of the agronomic properties of building materials. The results allow us to make recommendations for Living wall and Technosol design.