Spatial relationship of landform surface features and biocrusts, and their effect on soil microbial biomass on an alluvial fan

The spatial cover of biocrusts represents a suitable habitat for the activity of soil microorganisms in semi-arid and arid regions. Microorganisms are one of the essential components of soil quality. Therefore, it is necessary to understand the processes of biocrust habitat formation in landforms and their mutual relationship with soil properties. We studied the spatial distribution of biocrusts and their effect on soil microbial biomass and carbon activity in a semi-arid alluvial fan in NE Iran. A total of 72 soil samples (using plots 0.25 m2) from the topsoil layers (0-5 cm) were collected along the alluvial fan in September 2020. Soil surface properties and microbial biomass in two categories of biocrust and non-biocrust were investigated in three classes of biocrusts coverage obtained by geostatistics. Our results revealed that biocrusts had a negative correlation with gravel coverage and elevation; in contrast, the suitable spaces for biocrusts growth were created by cobble clasts. The biocrusts have provided favourable conditions for soil microorganisms by altering the properties of the soil (such as increasing organic carbon, nitrogen and available phosphorus and decreasing pH), and thus they increased basal soil respiration and microbial biomass. Different microbial activities were led by the predominant type of biocrusts, as the chlorolichen crusts had the most significant effect on increasing the microbial biomass phosphorus while cyanolichen crusts increased the microbial biomass carbon. Moss and cyanolichen crusts increased microbial activity and respiration more than cyanobacteria crusts. Therefore, the soil quality has improved by biocrusts in semi-arid ecosystems. Landform surface features influenced the distribution of biocrusts. Biocrust cover provided suitable habitat for soil microorganisms. Different types of dominant biocrusts promoted different microbial activity.image