In arid and semi-arid environments, soils are very fragile. Their degradation rapidly reduces the biological potential and disrupts the ecological and socio–economic balance. Living within a few millimetres of the soil surface, biocrusts are organised into communities of biota and play an important role in soil stability and preservation. They are mainly composed of cyanobacteria, lichens, mosses, fungi, eukaryotic algae and other heterotrophic bacteria. Soil–biocrusts interaction is therefore very important and a good knowledge of this interaction allows a better management of soils, especially in arid and semi-arid environments. Thus, the link between cyanobacteria species and physicochemical parameters and soil mineralogy was studied in two geomorphological zones of northeast of Iran. Cyanobacteria are the main photosynthetic component of biocrusts. Samples were collected in summer along a linear transect by using 50 x 50 cm quadrates for each study zone. Individual mineral soil particles were analysed by scanning electron microscopy (SEM). The amounts of Na, K, Ca and Mg as well as electrical conductivity and soil organic carbon are higher in the presence of biocrusts (Takhte Soltan site) than in their absence (Sabzevar Playa site). Biocrusts increased levels of organic carbon, pH, calcium carbonate, exchangeable sodium and potassium percentages. Results indicated that soil properties regarding soil organic carbon, CaCO3 and amount of clay changed among biocrust sand bare soils. This research considers further attention to biocrusts because of their multiple ecosystem roles and their importance in the constitution of dryland ecosystems.

Keywords