Int. J. Environ. Sci. Technol. (2016) 13:2521–2532 DOI 10.1007/s13762-016-1074-4 REVIEW Potentials of the microalgae inoculant in restoration of biological soil crusts to combat desertification A. Lababpour1 Received: 29 December 2015 / Revised: 1 July 2016 / Accepted: 12 July 2016 / Published online: 20 July 2016 Ó Islamic Azad University (IAU) 2016 Abstract The world is presently faced to the many application of the microalgae inoculant is an encouraging calamities, mainly the increased and rapidly developing aspect for accelerating the BSC recovery of the arid and environmental changes, soil degradation as an example of semi-arid areas. However, further researches will help to such environmental problems which is correlated with the establish and consolidate the potential of the microalgae destructive effects of the sandstorms. Biological soil crust cells and their application in desertification programs in (BSC), a main component of soil, has various environ- large scales and in accordance with principles and mental functions including reduction in the erosion by requirements mandated by economic standards. increasing soil stability and providing a sanctuary for the growth of the taxa and vascular plants communities. Keywords Biotechnological productivity Á Destruction of BSC, which naturally can be recovered Erosion control Á Microalgal mat Á slowly in a long time processes, contributes to the deser- Soil community restoration Á Soil health tification and other environmental catastrophes. Therefore, accelerating the BSC recovery both the quality and the quantity of the crust development, especially in the desert Introduction areas, is of the prime interest. Recent advances in the BSC restoration have provided an immense potential for emu- Biological soil crust (BSC) has been the subject of interest of lating the natural restoration methods mainly through scientist from different science sectors, governments, com- providing soils with inoculant. This paper reviews the munities, and international organizations such as United present restoration-based procedures for the biological soil Nations (UNCCD 2015). The main reasons for such a high crust restoration practice. The main landmarks are pre- interest in BSC are the function, the vital role that it plays in the sented and highlighted including strain(s) selection and environment, along with the impacts that its disturbance would development, mass biomass production, inoculum prepa- have on human life which threatens both the current, and the ration, soil inoculation, soil augmentation, nurseries, and future lives on earth (UNCCD 2015). BSC is commonly crust succession monitoring and control. The review also defined as the outer cohesive thin horizontal ground cover, introduces several successful case studies in the USA and which is associated along with the living constituent that plays a the Republic of China. Thereafter, the paper briefly docu- vital ecological supporting roles such as protecting and stabi- ments the future directions of the research and technolo- lizing the soil against water and wind erosive forces, especially gies. Development of a restoration system through the in the arid and semi-arid areas (Mor-Mussery et al. 2015). Annually, a large scale and increasing amounts of environmental disturbances happen because of the direct or & A. Lababpour indirect disturbances in the global soil crust (Rosentreter [email protected] et al. 2007). Several factors that cause BSC disturbances include climate change, soil degradation, desertification, 1 Department of Industrial and Environmental Biotechnology, National Institute of Genetic Engineering and Biotechnology, vegetation depletion, drought, and low precipitation (i.e., Tehran 14965-161, Iran rainfall) are among such factors. Loss of BSC and its 123 2522 Int. J. Environ. Sci. Technol. (2016) 13:2521–2532 destruction results in loss of its ecological functions lead- Ecology of BSC ing to the environmental consequences such as sand storms, reduction in soil stability, reduction in nitrogen and Often, the term BSC is referred to a consortium of auto- carbon fixation, water-related activities and effects on other trophic and heterotrophic living organisms in the outer soil microorganisms, and vascular plants will occur. The layer of the soil surface. They may also be called cryp- ultimate consequences of these destructive events may togamic, cryptobiotic (Clegg 2001), microbiotic, micro- affect health, economic and other aspects of human life, or phytic, and micropgytic soil crusts or soil- and rock-surface in the worse scenario, there may not be any chance of communities (SRSCs) (Pointing and Belnap 2012). Struc- adjustment left forever (Field et al. 2010). Both the natural turally, BSC consists of numerous kind of species includ- causes and human activities are the principal drivers of the ing prokaryotic cyanobacteria (Brostoff et al. 2005), processes of BSC degradation and desertification. In this diatoms, eukaryotic microalgae (Cardon et al. 2008), regard, artificial restoration of the BSC may help to put an lichen, mosses, fungi (Grishkan et al. 2015), liverworts, end and help the management of the desertification. bacteria (Mengual et al. 2014a), and other taxa. BSC may The various ecological functions of the BSC have been be subdivided based on its biotic components such as evidenced (Abdel-Raouf et al. 2012) through many func- cyanobacteria and microalgae crust (Karsten and Holzinger tions that have been attributed to the BSC in practice 2014a, b), lichen crust (Wu et al. 2011), mosses crusts, including soil erosion reduction and control (Belnap et al. fungi crust, and bacterial crusts (Wang et al. 2007). Table 1 2003). BSC performs its influence by aggregating uncon- represents some of the genera and species of the BSC solidated soil particle both by the physical net and/or by community. Geographically, BSC occurs in various areas releasing chemical substances such as polysaccharides and extreme habitats of the earth surface such as arid, hot, (Abdel-Raouf et al. 2012). This function is partly executed and cold desserts with a thickness ranging from few mil- by fixing the atmospheric carbon and nitrogen (Bu et al. limeters to several centimeters (Belnap et al. 2001). 2013) and stabilization of the chemical elements such as However, the community types and proportional amounts chromium in the soil (Belnap et al. 2003), thereby influ- of the biological components of the crusts vary in different encing soil organic and inorganic nutrient materials (Bel- ecosystem and climates (Pietrasiak et al. 2013). nap and Harper 1995). Further, BSC has a role in retaining The natural sequences of BSC community succession soil moisture, so improving soil hydraulic conductivity generally include the development of cyanobacteria and (Belnap et al. 2003) and soil infiltration. BSC improves microalgae, lichen and mosses, which is followed by other vegetation by helping germination of the seeds and inhi- organisms and vegetation (Belnap et al. 2001). Figure 1 bition of the weed, as well as protection against UV shows the stages of the BSC succession. Once a mat of (Belnap et al. 2003; Lan et al. 2014a). BSC also has been these organisms has become established, the diversity of used as an indicator of ecological integrity (Bowker et al. species increases through different succession stages and 2006). steps toward completion of the process (Bowker et al. The objective of this review article is to present a 2006). Therefore, in developing engineered plans and comprehensive review of the role of BSC and to provide a methods for BSC restoration, all succession steps such as summary of the present methods of the BSC engineering, field practice should be considered to meet the desired crust BSC restoration, and the challenges that might be formation. encountered in this respect. The review mainly focuses on the crust microalgae as effective pioneer microorganisms in the restoration of the BSC. In addition, the main crust Conventional systems of BSC restoration microalgae succession steps are explained and a number of successful implementation is introduced, accordingly. The Several options are available to protect degraded crusts or article discusses the artificial BSC restoration following to accelerate the natural BSC restoration. Selection of the an introduction, BSC definition, ecology, functions, roles, methods is mainly dependent on the location and the and the natural succession. This paper provides a critical conditions of damaged crust. For example, in deserts with review on microalgal-based BSC restoration. The main high speed winds, a frequently used conventional approach stages of strain(s) selection and development, mass pro- is wind shelter or check boards to provide protective con- duction of microalgae, inoculant preparation, soil inocu- ditions in the early crust development stages. In addition, lation, soil augmentation, nurseries, and restoration process land chemical mulching such as petrochemical is also used monitoring and controlling are highlighted. Challenges and as pretreatments. Mulching inhibits soil erosion by pro- future directions on BSC restoration with microalgae spe- viding a cover layer on the soil surface. However, the cies are also outlined. efficiency of the mulching is dependent on the mulch layer 123 Int. J. Environ. Sci. Technol. (2016) 13:2521–2532 2523 Table 1 Examples of the most common genera and species of the microorganisms in the natural BSC communities Cyanobacteria and microalgae Lichen (Belnap