Biological soil crusts: Recent advances in our knowledge of their structure and ecological function

Biological soil crusts (BSCs) result from an intimate association between soil particles and cyanobacteria, algae, microfungi, lichens, and bryophytes. These crusts are widespread in many type of soils and in almost all plant communities where sunlight can reach the soil surface. However, BSCs are particulary dominant in environments with low productivity such as arid, semi-arid, alpine and polar areas. Biological soil crusts affect soil nutrient cycling, influence the local hidrological cycle, increase soil stability, and affect the establisment and performance of vascular plants. The knowledge on the biology, ecology and physiology of BSCs has substantially increased in recent years. However, there are important gaps in our knowledge concerning the influence of BSCs on biogeochemical cycles, particularly of phosphorus and carbon, as well as on many aspects related to biotic interactions among BSC components, and between these components and microorganisms, vascular plants and invertebrates. It is necessary to expand current research efforts to other parts of the world, as most studies have been conducted mainly in arid and semi-arid areas of USA, Israel, Australia and China. Of particular concern is the lack of studies from Central and South America, despite BSCs must be a key biotic component in countries such as Chile, Argentina, Peru and Mexico. With the aim of increasing the interest of the scientific community of Spanish-speaking countries about this important group of organisms, in this review we illustrate recent advances on the importance of BSCs to maintain the structure and functioning of those ecosystems in which they are present. We also highlight the main gaps in our knowledge on the ecology of these organisms, and discuss key areas for future research.