Exopolysaccharides synthesized by cyanobacteria residing in Induced Biological Soil Crusts increase stability and carbon organic content of desert sandy soils

The introduction of Biological Soil Crusts (BSCs) in degraded soils through inoculation-based techniques (IBTs) is considered a valid pathway to counteract soil-loss and to expand cultivable areas. BSCs introduce high amount of C in the soil as extracellular polysaccharides (EPSs), mostly produced by the crustal phototrophic fraction. IBTs using ex-situ cultured cyanobacterial biomass were reported to induce crust formation and represent an exploitable system to increase soil fertility. Such a technology was applied in Hobq desert, China, where different sites constituted initially by bare sandy soil were inoculated with a mixed culture of EPS-producing cyanobacteria. We investigated the effects of IBT in terms of soil C gain and phototrophic abundance. EPSs, extracted from the crusts, were analyzed for their monosaccharidic composition and molecular weight (MW) in order to investigate possible differences related with crustal development stage. Results showed that BSC induction led to a significant increase in soil total carbohydrate content and phototrophic abundance compared to control areas. EPSs showed to be constituted by moieties with different MWs and a notable complexity in terms of monosaccharidic composition, suggesting the major share of cyanobacteria in their synthesis. The outcomes of this study underline the potential of the IBT method in restoring Soil Organic Carbon content, and represent a first step in field studies regarding EPS dynamics in BSCs.