Restoring soil functions by means of cyanobacteria inoculation: Importance of soil conditions and species selection

In recent years, soil inoculation with cyanobacteria has become one of the most promising biotechnological strategies for restoring soil functionality in degraded drylands because of their critical role in increasing soil fertility and preventing erosion. Nevertheless, in order to fully exploit this biotechnology on a large scale, it must still be shown whether inoculated cyanobacteria are capable of developing in soils with different physicochemical properties, and new candidates adapted to desert conditions must be explored. To evaluate the potential of cyanobacteria for restoring soil functions of degraded dryland soils, in this laboratory study, we analyzed the effect of inoculating three native N-fixing species (Nostoc commune, Scytonema hyalinum, and Tolypothrix distorta), individually and as a consortium, on soil properties from three different semiarid ecosystems in southeast Spain. The biocrust colonization was monitored by determining chlorophyll a content (the typical surrogate used for biocrust biomass). Other methodologies, such as the analysis of soil spectral response and image classification were also applied for cover estimation of the biocrust. After 3 months, all inoculated soils showed cyanobacteria cover of up to 50%, lower albedo and higher chlorophyll a content. Cyanobacterial inoculation also improved soil functions, as they promoted a significant gain in total organic carbon and total nitrogen in all soils. Among inoculation treatments, Nostoc commune and the mixture of all three species promoted the most cyanobacteria coverage, chlorophyll content, and surface darkening, as well as organic carbon and total nitrogen gains in the soil, highlighting their excellent performance in biocrust development.