Desert biocrust was highly specialized communities composed of cyanobacteria, green algae, lichens, mosses, bacteria, and microfungi (Chock et al., 2019). Desert biocrust might be classified as cyanobacterial crusts, lichen crusts, or moss crusts based on their successional stage and dominant components (Antoninka et al., 2016; Bustos et al. 2022; Chiquoine et al., 2016; Kidron, 2015; Zheng et al., 2011). The organisms comprising biocrusts could adapt to extreme environmental conditions such as high temperature, salinity, low precipitation, strong irradiation, and desiccation (Felde et al., 2018; Hui et al., 2022; Ji et al., 2019; Rao et al., 2012; Zhao et al., 2016), they could also fix mobile sand dunes as well as alter topsoil moisture and resistance to wind and water erosion, improve carbon and nitrogen fixation and nutrient cycling, resulting in improvement of the surrounding environment and regulation of soil microbe abundance and community diversity (Aranibar et al., 2022; Drahorade et al., 2022). Additionally, desert biocrust could improve soil fertility through mineral chelation, dust entrapment, and metabolism, which is beneficial to invertebrates and reptiles, as well as vascular plants (Rajnoch et al., 2022; Sinsabaugh et al., 2015; Strong et al., 2013; Zhang et al., 2015; Zheng et al., 2018; Zhou et al., 2016;). Accordingly, desert biocrusts were considered a solution for the restoration of degraded desert soil.
Natural self-recovery of desert biocrust to a stable succession state could take several decades to millennia although the self-recovery of desert biocrust in desertification land happened all the time (Chock et al., 2019), the colonization of vascular plants usually occurred after biological crusts improved the topsoil environment, it could take a long time, the natural recovery of desert biocrusts from disturbance taken especially long and was highly variable from place to place (Giraldo-Silvaet al., 2019; Lan et al., 2014). In addition, changes in climatic conditions (temperature and precipitation) have a great impact on the growth of desert biocrust. The occurrence of extreme weather tends to inhibit soil respiration in biocrusts (Ayala-Nino et al., 2022; Guan et al., 2021). Many researchers had conducted experiments investigating the rapid artificial induction of biocrusts through the use of moss and cyanobacteria (Kidron et al., 2015). Chen et al. (2006) constructed man-made desert algal crusts in Inner Mongolia, China, by inoculating Microcoleus vaginatus onto unconsolidated sand dunes. Wang et al. (2013) also tested the feasibility of mixed cyanobacterial inoculation with straw checkerboards and automatic-sprinkling microirrigation techniques in desert areas. The soil fertility and microenvironment of the topsoil improved as cyanobacterial crusts developed (Park et al., 2017). Different soil substrates also affect the colonization of artificial biocrusts. Zhao et al. (2021) successfully cultivated artificial biocrusts in field conditions by broadcasting natural cyanobacteria and cyanobacteria-lichen crust fragments. They found that left-over soils from dredged irrigation channels and abandoned farmlands can provide a good substrate to culture desert biocrusts inoculum material. Although the aforementioned studies provide some useful information regarding artificial biocrust generated using cyanobacteria, it was still unclear how efficiently cultured biomass of cyanobacteria could be used for artificial biocrust formation. Because extremely large numbers of desert biocrust cells should be cultured in the laboratory or by other equipped facilities to induce artificial biocrusts in a large area, the amounts of desert biocrust biomass that were sufficient to induce the formation of biocrusts strong enough to prevent destructive stresses in the field should be determined.
During artificial propagation of desert biocrust, growth-favoring environmental conditions were often helpful to rapidly form the biocrust (Hui et al, 2018, 2014, 2012; Park et al., 2017; Tao et al., 2021). Thus, these conditions might be used for later application in the field where environmental factors are variable and sometimes are harsh (Bu et al., 2017). Some artificial propagation methods of desert biocrust were developed and confirmed that they were practical (Antoninka et al., 2016; Szyja et al., 2018; Zhang et al., 2021). Therefore, developing the artificial propagation methods towards wider and larger-scale field applications was widely anticipated.
Many chemical agents, such as organic polymers, had been investigated for sand stabilization because they play an important role in increasing sand stability and protecting sand particles against wind erosion. To prevent wind and water erosion in arid or semiarid areas, sand-fixing agents such as polymerized by the monomer of vinyl acetate (PVIN), polyvinyl alcohol, poly (aspartic acid), and polyacrylamide have been used. These chemical agents were normally less expensive than physical (mechanical) and vegetative materials (Ma et al., 2016), and effective at fixing sand particles in the short term but are not reliable and sustainable in the long term due to microbial degradation (Rozenstein et al., 2014), exposure to strong UV radiation, and temperature fluctuations in the field (Hui et al., 2014, 2012). Conversely, biocrust formations were more appropriate for fixing sand and restoring damaged soil in arid areas. However, it will take several years, or even a few decades, to induce biocrust formation in nature depending on environmental conditions during the initial stage. The combined application of biological materials and chemical agents could accelerate biocrust formation under natural conditions compared to the application of individual cyanobacteria or chemical agents. The biological and chemical agents could physically fix fine sand particles in a short period, which was crucial to desert algae settlement for biocrusts induction on bare sand soils, while also increasing water availability for desert algae crust growth due to their high water-absorbing capacity (Hui et al., 2018; Park et al., 2017; Shi et al., 2016). Thus, the double action of the sand-fixing material could enable more rapid induction and stable formation of biocrusts than the application of desert algae crust alone under natural conditions. Moreover, the combined application of sand-fixing material with desert biocrust could overcome the defects associated with sand-fixing material during field trials.
China was one of the most vastly desertification countries in the world, there was 2.63 million km2 of desertified land, which accounted for 27.3% of the total national territory. The lack of water resources and precipitation, high water dissipation severely restrict the ecological model and process of desert ecosystem (Cheng et al., 2022). Efforts to counter desertification had been initiated over the past few decades; however, only a small improvement had been arrived. This was of great concern, as desertification was the leading problem inhibiting development in China, especially in northern and northwestern China. At present, researches on rapid cultivation of moss crust in China and elsewhere mainly focus on indoor tissue culture, artificial repair of wild biological crust and influencing factors. Recently, several artificial cultivation methods of desert biocrust were developed, confirming that the technology of rapid artificial inoculation of biocrusts was practical (Antoninka et al., 2016; Wu et al., 2013). The propagation of biocrusts often performed some particular growth responses under variable environmental conditions. Can the artificial biocrust prepared with different materials and methods survive and grow under different combined inoculation application and water supply? The present studies were conducted to induce biocrust formation through the use of biological sand-fixing material and to facilitate stable and rapid formation of biocrust. The biological sand-fixing material added attapulgite were applied as a sand-fixing and water-retaining agent under early stage of biocrust succession. The inoculation of biological sand-fixing materials was conducted to investigate the effects of inoculation times and water supply in order to evaluate the feasibility of application and potential methods for cultivation of biological sand-fixing material for promoting establishment of desert biocrusts.