Due to global warming, in addition to higher temperatures, extreme weather events will also occur more frequently in the future, which will have a considerable impact on agriculture. In addition, longer periods of heat will lead to progressive desertification. Irrigation during hot spells cannot be guaranteed, so ideally the water must be kept in the soil for longer. In this project, the scientific and process-technical foundations are to be created to be able to use phototrophic biofilms to improve water retention in the soil and for the rehabilitation of degraded land. Phototrophic biofilms consist, among other things, of phototrophic microorganisms that are present in a self-produced matrix that protectively surrounds the cells. This matrix consists of extracellular polymeric substances (EPS). At present, however, there is a lack of in-depth understanding of the adaptation mechanisms of phototrophic biofilms and of the swelling and shrinking behaviour during periodic de- and rehydration, which is essential for water retention. Within the proposed project’s scope, phototrophic biofilms are to be screened and characterised with regard to their drought tolerance. An important aspect here is the ability of anhydrobiosis. Anhydrobiosis is the ability to regain full vitality after complete dehydration. Furthermore, the kinetics of the swelling (water uptake) and shrinking (water release) behaviour of the phototrophic biofilms is of interest, as well as the influence of the self-produced EPS on this behaviour. In order to characterise the phototrophic biofilms during periodic rehydration and dehydration and to understand the mechanisms behind this, the biofilms will be cultivated in aerosol-based photobioreactors in a surface-associated manner and the influence of temperature and drying stress on the swelling and shrinkage behaviour will be investigated. Furthermore, a correlation between biofilm morphology (layer thickness, surface roughness, void distribution) and desiccation tolerance will be established, generating extensive knowledge on water uptake, storage and release of phototrophic biofilms. It is known that some biofilms form voids that can be filled with water more quickly when rehydrated. It is to be investigated how drying condition, void distribution and water retention will influence the mechanical properties of the biofilm. Investigations of the biofilms in the rheometer will provide important insights into elasticity and viscosity as well as resistance to (shear) and their adhesive forces. In a final work package, the previously gained knowledge will be used to produce biofilms adapted to optimised water storage.