Spatial heterogeneity of Cladonia rangiformis and Erica spp. induces variable effects on soil microbial communities which are most robust in bare-soil microhabitats

Abstract. Biological soil crust (BSC) is an essential part of arid and semiarid regions; however information concerning the spatial heterogeneity of the interactions between crust, plants and soil microbes is limited. Sampling was confined to an area either covered with Erica spp. shrubs interspaced by crust cover (Cladonia rangiformis) or uncovered by crust. Along a straight line of 100 cm from the base of the shrubs towards their periphery and at successive distances of 20 cm, soil samples were collected once. The biomass, the composition and the network of interactions among the members of the soil microbial communities as well as the activity of soil enzymes involved in the C, N and P cycle were estimated. Crust coverage exerted a significant allelopathic negative effect on soil microbial biomasses due to the leaching of lichen's antimicrobial substances. In contrast, the crust effect on enzyme activity was positive, probably due to the amelioration of soil abiotic conditions. The distance from the base of Erica spp. affected the total microbial and bacterial biomass, with lower values at the base of the shrubs. The composition of microbial communities between the different sampling points exhibited significant dissimilarities. Network analysis revealed that in uncrusted soils the most connected microbial network was at samples collected from a distance of >60 cm (bare soils), while in crusted soils this was at samples collected at the base of shrubs. We concluded that microbial biomass showed limited response to spatial heterogeneity, while the composition and the topology of interactions among the microbial members reflected a heterogeneous soil environment existing on a small spatial scale in Mediterranean areas. The microbial community in bare soil appeared to be the most robust against future disturbances.