Soil restoration by cyanobacteria inoculation: relationship between cyanobacterial polysaccharidic matrix and soil properties

Inoculation of soils with cyanobacteria is proposed as a sustainable biotechnological technique for restoration of degraded areas in drylands due to the important role that cyanobacteria and the exopolysaccharides (EPS) they secrete play in the environment. Cyanobacterial EPS increase the soil organic carbon pool and improve aggregation and porosity, thus favoring infiltration and water retention and improving soil water status and soil fertility. Cyanobacteria filaments and their EPS strongly increase soil stability, improving soil resistance to wind and water erosion. Cyanobacteria inoculation was demonstrated to artificially determine the development of biocrusts. So far, only a few studies have explored the relationships between the characteristics of the cyanobacterial polysaccharidic matrix, the development of artificially inoculated biocrusts, and their effects on soil properties. This information is crucial to select the most suitable cyanobacterial candidates for restoration of damaged dryland areas. The objective of this study was to examine the growth curve of two cyanobacteria species, Phormidium ambiguum (non N-fixing) and Scytonema javanicum (N-fixing), and the effects of their inoculation on biocrust development and soil properties in different textured soils, under laboratory conditions. The macromolecular and chemical characterization of the polysaccharidic matrix developed by both species on the inoculated soils was also analyzed. Cyanobacteria inoculation led to a more significant improvement in soil fertility properties in the soils with initially lower physico-chemical quality. S. javanicum promoted a higher increase in soil organic carbon and nitrogen content, likely associated to the higher amount of water-soluble EPS synthesized by this species, while P. ambiguum was more effective in increasing soil surface resistance, likely associated to the larger amount of EPS less soluble and with a higher degree of condensation synthesized by this cyanobacterium. Our results highlight the importance of the cyanobacterial polysaccharidic matrix for biocrust development and its role in improving soil properties and functions.