Polysaccharidic matrix formation in induced biocrusts is affected by soil type and inoculated cyanobacterial species

The induction of biocrusts by inoculating soils with cyanobacteria has been proposed as a sustainable technique for restorating degraded areas owing to the role that cyanobacteria and the exopolysaccharides (EPS) they secrete play in improving soil properties. Nonetheless, only few studies have analyzed the characteristics of the EPS matrix excreted by cyanobacteria in soil crusts, so far only focusing on sandy soil textures. The objective of this study was to examine the characteristics of the EPS matrix induced under lab conditions by inoculating two cyanobacteria, Phormidium ambiguum (non N-fixing) and Scytonema javanicum (N-fixing), on four differently textured soils and to follow for 90 days the development of biocrusts, measuring their physical and ochemical features. Cyanobacteria inoculation led to biocrust formation in all soil types, especially in those with …. texture. SEM images showed that the biocrusts induced by P. ambiguum were characterized by a dense, entangled network of thin filaments enveloping soil particles, while those induced by S. javanicum consisted of bunches of thicker filaments grouped in between soil particles. S. javanicum promoted a higher release in the soil of the less condensed EPS fraction (LB-EPS), while P. ambiguum showed a higher release of the more condensed EPS fraction (TB-EPS). LB-EPSs were mainly composed of low MW molecules, while TB-EPSs were mainly composed of high MW molecules. The two EPS fractions showed a complex monosaccharidic composition (from 11 to 12 different types of monosaccharides), with glucose as the most abundant monosaccharide, in particular in the poorer soils poorer , characterized by lowerin organic C contents. Cyanobacteria inoculation also improved soil fertility, in particular in those soils that originally were less fertile. Our results point out that both the development of induced biocrusts and the characteristics of the EPS matrix are significantly affected by the cyanobacterial species inoculated and by the texture of the soil treated.