# Cyanobacterial Potential for Restoration of Loess Surfaces through Artificially Induced Biocrusts
## 4 Discussion
### Particle Trapping and Stabilization by Cyanobacteria  
After 10 months and 37 simulated dust storms that dispersed loess particles over the well-developed cyanobacterial biofilm in the experimental chamber (Figure 3A), a several millimeter-thick biocrust was formed (Figure 3B). Simultaneously, a layer of loosely aggregated loess particles formed in the control chamber (Figure 6C,D). Early-stage cyanobacterial crusts usually make a smooth crusted surface, while pinnacled crusts are usually formed by lichens and mosses [38, 105]. Due to the smooth surface they made, cyanobacterial crusts are regarded as having a lower potential for dust capturing, unlike lichen and mosses [38]. However, we observed several different morphologies of biocrusus including smooth, curled, and pinnacled biocrusts, of which the latter two have an increased surface for capturing the dust particles. Assessment of species composition in different morphotypes of biocrusts formed in this study will be the next step in studying the cyanobacteria-particle interactions. Furthermore, this study confirmed the ability of dry cyanobacterial biocrusts to reactivate their metabolic activity after wetting (Figure 5). The metabolic response to wetting is also reflected in the increased concentration of Chl \(a\) (Figure 10). It is known that cyanobacterial biocrusts can survive even under the extremely dry conditions of the Negev desert (<87 mm precipitation annually), protecting the surface from erosion and supporting the accumulation of dust particles by using the dew alone as a water source [106]. In some cases, biocrust cyanobacteria need, however, liquid water to reactivate their photosynthetic metabolism [107]. A bigger volume of biocrusts was also observed in the wet state (Figure 5), which is in line with the ability of biocrust cyanobacteria to swell rapidly up to 10 times their dry volume [108]. A more dense biological cover over the sediment observed during wet periods results from the cyanobacterial ability to follow water and glide to the biocrust surface during the wet events and to the deeper layers of biocrusts during dry periods [63]. Biocrusts have an important function in dust deposition [109], through dust particle trapping, accumulation, and consequently stabilization [9, 10]. The potential of biocrusorganisms to trap airborne particles is already known [38; 106; 110]. Cyanobacteria trap the particles mechanically through their filaments and by sticky EPSs [41]. Experiments in this study showed that the trapping of particles highly depends on the morphology of cyanobacterial colonies. Particles were either trapped within the network of cyanobacterial filaments and their tubular EPS (TB-EPS) or adhered onto the carpet-like superficial layer of amorphous cyanobacterial colonies and their slimy EPS. The same style of particle trapping was also observed by [PERSON] et al. [110] in the BLCs from North Iran. Our study also confirmed earlier observations of [PERSON] et al. [40] on cyanobacterial ability to form pinnacles. In our experiment, cyanobacteria formed pinnacles that rose above the biocrust surface and increased their roughness, which could significantly contribute to particle trapping. According to [PERSON] et al. [38], the morphology of biocrusts controls the amount of dust accumulation, where biocrusts with higher surface roughness enable higher accumulation of dust. Our observations on the mechanism of particle immobilization of coarser and finer particles are in line with earlier findings [40; 41; 110]. Coarser particles were mostly surrounded by the filament network, or covered by the amorphous EPS, while the finest particles were sticking to the EPS surface. We also observed that the filaments spread between the nearby particles, creating an organic bond between the adjacent loess particles (Figure 8A,D, arrow 1).