Cyanobacteria Inoculation Improves Soil Stability and Fertility on Different Textured Soils: Gaining Insights for Applicability in Soil Restoration

Abstract

Cyanobacteria are ubiquitous components of biocrust communities and the first colonizers of terrestrial ecosystems. They play multiple roles in the soil by fixing C and N and synthesizing exopolysaccharides, which increase soil fertility and water retention and improve soil structure and stability. Application of cyanobacteria as inoculants to promote biocrust development has been proposed as a novel biotechnological technique for restoring barren degraded areas and combating desertification processes in arid lands. However, previous to their widespread application under field conditions, research is needed to ensure the selection of the most suitable species. In this study, we inoculated two cyanobacterial species, Phormidium ambiguum (non N-fixing) and Scytonema javanicum (N-fixing), on different textured soils (from silt loam to sandy), and analyzed cyanobacteria biocrust development and evolution of physicochemical soil properties for 3 months under laboratory conditions. Cyanobacteria inoculation led to biocrust formation in all soil types. Scanning electron microscope (SEM) images showed contrasting structure of the biocrust induced by the two cyanobacteria. The one from P. ambiguum was characterized by thin filaments that enveloped soil particles and created a dense, entangled network, while the one from S. javanicum consisted of thicker filaments that grouped as bunches in between soil particles. Biocrust development, assessed by chlorophyll a content and crust spectral properties, was higher in S. javanicum-inoculated soils compared to P. ambiguum-inoculated soils. Either cyanobacteria inoculation did not increase soil hydrophobicity. S. javanicum promoted a higher increase in total organic C and total N content, while P. ambiguum was more effective in increasing total exopolysaccharide (EPS) content and soil penetration resistance. The effects of cyanobacteria inoculation also differed among soil types and the highest improvement in soil fertility compared to non-inoculated soils was found in sandy and silty soils, which originally had lowest fertility. On the whole, the improvement in soil fertility and stability supports the viability of using cyanobacteria to restore degraded arid soils.

Surface indicators are correlated with soil multifunctionality in global drylands

“…Biocrusts become more dominant in areas of increasing mean annual temperature and aridity, which could explain why increases in annual temperature, or declines in seasonal precipitation, were associated with positive effects of surface stability on soil multifunctionality, and C, N and P functions. Potential mechanisms accounting for greater stability include physical protection of the surface by lichens and bryophytes, capture of sediment by mosses and greater aggregate stability provided by fungal hyphae and extracellular polysaccharides in cyanobacterial sheath material (Chamizo, Mugnai, Rossi, Certini, & De Philippis, ). Intact surfaces might be expected to have a richer community of biocrust organisms that undertake a greater number of functions associated with mineralization of nutrients.…”

Spectral Response Analysis: An Indirect and Non-Destructive Methodology for the Chlorophyll Quantification of Biocrusts

“…Biocrusts' capacity to fix atmospheric carbon and nitrogen, as well as their role in all other key soil surface properties and processes, is mainly driven by the biomass of photosynthetically active organisms within the biocrust community [14] that have been demonstrated to be one of the best indexes of biocrust development [15,16]. Moreover, it is known that chlorophyll can be used to assess biocrust states in response to seasonal dynamics [17,18], anthropogenic disturbances [19,20], ongoing climate changes [21,22], and restoration activities [23,24]. For all these reasons, large efforts have been devoted during the past decades to obtain reliable measurements of biocrust chlorophyll concentrations [25][26][27].…”

Water Regulation in Cyanobacterial Biocrusts from Drylands: Negative Impacts of Anthropogenic Disturbance

“…This crust decreases hydraulic conductivity, limits infiltration, and favors the generation of runoff [82][83][84]. Cyanobacterial colonization on these soils usually enhances microtopography [29,41], improves soil aggregation and stability [22] and increases porosity [85,86], thereby enhancing infiltration. Thus, at the El Cautivo site, increased roughness in the more developed cyanobacterial biocrusts (Cc), in relation to the incipient ones (ICc), (Table 1) surely contributes to facilitate water percolation into the soil [29,41,85].…”

“…In this sense, Miralles-Mellado et al [85] found that pore occurrence in soils covered by cyanobacteria was related to EPS and the ability of filaments to adhere to one another and bind soil particles, and hence affect the soil's spatial organization. Besides, the capacity of cyanobacteria to secrete EPS compounds strongly increases organic carbon content [22,89] and water retention capacity of soils [90]. It has been shown that water holding capacity at field capacity can be 1.2 times higher (on silty loam soils, [31]) or from 2 to 4 times higher (on sandy soils, [85]) in soils with high than with low cyanobacterial cover.…”