# Cyanobacterial Potential for Restoration of Loess Surfaces through Artificially Induced Biocrusts
## 4 Discussion
### Particle Trapping and Stabilization by Cyanobacteria
Even though large pores between the particles hinder the spreading of the filaments [56], organic bonds between distant particles [51; 56] reduce the space between them and allow cyanobacteria to spread more quickly and easily. Clogging the large pores with fine particles could also facilitate the spread of colonies while keeping the particles immobilized. The airborne particles in loess landscapes are the source of essential mineral nutrients for the biocrust organisms [9]. Since in this experiment the addition of nutrient medium did not occur more than once a month, the loess particles were probably the main source of mineral nutrients. Weathering of immobilized particles through mineral dissolution is the mechanism by which mineral nutrients are acquired. As observed in this study, weathering was promoted by both TB-EPS and amorphous EPS, in and around the contact zone with the particles (Figure 9A-C). The precipitation of minerals on the EPS surface was also observed in this study. Furthermore, the precipitation of minerals in the contact zone between EPS and particles led to the formation of organomineral structures which improved the binding capacity of EPS to the particles. The same structures, referred to as cement between EPS and particles, were earlier described by [PERSON] et al. [40] and [PERSON] et al. [110]. We also observed that mineralized EPS structures surround and immobilize particles in the subcrust layer of induced biocrusts (Figure 9D), thereby improving the cohesion of the biocrust. Certainly, the organomineral structures observed in this and previous studies, allow a permanent immobilization, aggregation and stabilization of the loess particles [10; 51]. Strain Selection Criteria and Perspectives on the Application of Cyanobacteria in the Restoration of Exposed Loess Sediments  
Criteria for the selection of strains to be used as inoculum in the restoration of disturbed land surfaces should include information on as many strain characteristics as possible to ensure the formation of sustainable biocrusts that are effective in sediment stabilization. In this study, we investigated various characteristics, including toxin, biomass and polysaccharide production and the interaction between cyanobacterial colonies and loess particles. The strains used in this study were isolated from biocrust samples taken from loess sediment surfaces in Serbia, which meets the need to use native species to avoid the possible introduction of alien or invasive taxa [111]. Previous analyses of desert biocrusts indicated the potential of terrestrial cyanobacteria to produce cyanotoxins. [PERSON] et al. [112] identified cyanotoxin presence in desert biocrusts, which was later confirmed by [PERSON] et al. [113; 114] and [PERSON] et al. [115]. The studies showed that desert biocrusts from Qatar contained microcystins, anatoxin-a(S), beta-N-methylamino-L-alanine (BMAA), 2, 4-diaminobutyric acid (DAB), and N-(2-aminoethyl) glycine (AEG). In addition, possible traces of microcystins were detected in two Iranian BLCs at a concentration of a few ng/g detected using a protein phosphatase inhibition assay, while the _Artemia salina_ mortality test indicated the presence of toxicity in one sample [110]. Toxicity assessment is a necessary step in the selection of cyanobacterial strains for land restoration because of the observed toxins. In this study, none of the strains tested caused mortality higher than 50% of the brine shrimp larvae, which condones their use in the practice of land restoration. Ease of cultivation and efficiency in biomass production may be preferred in selection of strains for restoration. In our study, the strain _Nostoc_ sp. L5 achieved the highest biomass after seven weeks of cultivation in BG11 N+ medium and could therefore be a strain of choice for field application. However, species with a high biomass production under culture conditions may not perform equally well under natural conditions, and this may apply in particular to strains cultivated in BG11 N+ medium.