Intimate Association
Where climatic conditions are harsh or disturbances reduce common plant coverage, biological soil crusts (BSCs) are established. These BSCs are groups of photosynthetic organisms like algae, mosses and lichens, that live within and on top of soil surfaces and co-occur with bacteria and fungi. As a skin, BSCs cover up to 12% of the Earth’s land surface from deserts to polar environments \cite{Rodriguez_Caballero_2018}. With their root- and rope-like structures, and by the excretion of sugar-containing glue-like substances, BSCs bind soil particles and stabilise surfaces against erosion. BSCs are therefore considered to be ecosystem engineers (Figure 1).