Life on earth depends on the soil, supporting key ecosystem processes (such as the nutrient and hydrological cycle), and containing a large number of global biodiversity (such as microorganisms, small and medium-sized animals) (Eldridge et al., 2020; Guerra et al., 2020). There is a ubiquitous pattern of uneven distribution of soil characteristics in the terrestrial ecosystems, which is known to regulate a wide range of ecosystem processes, including nutrient cycling (Ochoa-Hueso et al. 2018), trophic interactions (Tsunoda et al. 2014), individual plant performance and competitive ability (Day et al. 2003), and community-level productivity (Maestre and Reynolds 2006). Most terrestrial ecosystems have patchy distributions of soil resources (García-Palacios et al., 2012; Lozano et al.,2013), especially in dryland, where the landscape is organized into a mosaic of resource-rich and resource-poor in vegetated and unvegetated patches (Ludwig and Tongway, 1995). The spatial variation in soil multifunctionality (SVM) in drylands is likely to be caused by the significant multifunctional differences between vegetated patches, in which plants largely drive biological processes such as litter decomposition, carbon and nitrogen fixation and nutrient cycle, and unvegetated areas, in which physical functional processes such as wind and water erosion play a larger role (Li et al. 2007; Duran et al., 2018; Zheng et al., 2019). This SVM is regulated by the interactions among biotic and abiotic processes (Garner and Steinberger, 1989; D’Odorico et al., 2007; Allington and Valone, 2014; Ochoa-Hueso et al., 2018) and is likely to cause a variable pattern of soil multifunctionality (MF) (Manning et al., 2018) among the landscape (Duran et al., 2018). Due to the sensitivity of these areas to climate change, increasing aridity and temperature would lead to change in vegetation and soil properties that could adversely affect SVM in drylands worldwide. Therefore, changes in climate and plants are associated with alterations of the SVM in drylands (Duran et al., 2018; Ding and Eldridge, 2021). According to recent studies, increasing aridity is correlated with decreasing plant cover and richness, and increasing woody vegetation encroachment rates across the globe (Dougill and Thomas 2004, Vicente-Serrano et al. 2012, Delgado-Baquerizo et al. 2013), which would likely lead to an increase in SVM.
The SVM plays a key role in the sustainability and stability of ecosystem functions (Juhos et al., 2016). Different physical, chemical, and biological aspects mainly characterize the soils (Bouma, 2002). They influence MF, soil quality (SQ), and, subsequently, the ecosystem process. SQ is defined as the ability of soil to function within land use and ecosystem boundaries, sustain biological productivity, preserve environmental quality, and enhance plant, animal, and human health (Doran and Parkin, 1994). The change of SQ is related to the changes of complex factors; it is usually the result of many interaction processes that may upset the balance between soil physicochemical, microbial and biochemical properties (Hedo et al., 2014). Therefore, the multifaceted functional concept cannot be measured directly in the field or laboratory but rather must be derived from the soil properties and processes that are sensitive to land use and management. These are referred to as soil quality indicators (SQIs) (Zornoza et al., 2015). For monitoring SQ, multivariable indices are the best because they provide a broader view of the situation than individual property analyses. Evaluating whether desert soil SQI and SVM are affected by the environment will help to understand desert ecosystem processes further.
Drylands are crucial for global sustainability, as they constitute 45% of the earth’s land surface (Pravalie, 2016; Reynolds et al., 2007), where many vascular plants are restricted due to the shortage of precipitation; however, biological soil crusts (BSCs) are widespread. Recent estimates indicate that BSCs currently cover about 12% of the earth’s terrestrial surface and about 30% of dryland soils (Rodriguez-Caballero et al., 2018). BSCs are compose of cyanobacteria, green algae, lichens, mosses, and other organisms related to soil particles that play essential fundamental roles in arid and semiarid regions (Belnap and Lange, 2003; Li, 2012; Xiao et al., 2022), including C and N cycling (Bowker et al., 2013; Hu et al., 2014; Li et al., 2019a), surface energy balance (Couradeau et al., 2016; Rodriguez-Caballero et al., 2015; Rutherford et al., 2017), erosion (Canton et al., 2014; Chamizo et al., 2017; Zhao and Xu, 2013; Knapen et al., 2007) and water redistribution (Bowker et al., 2013; Kidron et al., 2012; Kidron and Vonshak, 2012; Kidron and Tal, 2012; Kidron and Budel, 2014), affecting the colonization and development of vascular plants (Langhans et al., 2009; Li et al., 2005), and supplying habitats for other microorganisms and protozoa (Liu et al., 2017). The formation and succession of BSCs can significantly influence the characteristics of soil nutrient cycling and affect the soil layer 2–5 cm below the BSCs patch (Gao et al., 2018). During biological crust succession, there are coupling and synergistic changes between soil properties and microbial communities. There will also be significant differences in the physical and chemical characteristics of the underlying soil under different types of crust, which will affect the microbial diversity and enzyme activity in the soil (Li et al., 2020; Li et al., 2021). The biological crust can fix C, N, and activate P, significantly enhance the content of C, N, and P in surface soil, and change the stoichiometric characteristics of soil (Baumann et al., 2021; Zhang et al., 2022). Therefore, BSC actively participates in soil surface heterogeneity dynamics in terms of biological diversity and soil function and physicochemical properties associated with their spatial structure (Ettema and Wardle, 2002).
Desert environments easily affect the distribution, growth, stoichiometry, and species composition of BSC. Unlike vascular plant patches, BSCs are generally located within the uppermost millimeters of the soil surface (Weber et al., 2022); they are more likely to be affected by environmental factors, such as soil water, soil nutrients, temperature, and radiation intensity (Grote et al., 2010; Navas Romero et al., 2020). SM variability can be altered by changes in aridity and rainfall seasonality, which can influence the formation and growth of BSC, soil properties (soil texture, pH) by physical processes, such as wind erosion, aeolian deposition, rock weathering, and soil leaching (Delgado-Baquerizo et al., 2013; Berdugo et al., 2020). As a result, the soil nutrients in the soil under BSC patches are also affected by environmental changes and are significantly higher than those in soil without BSC (Li et al., 2019a; Tao et al., 2020). However, few studies have explored the effects of BSC patches on soil function and physicochemical properties. Hence, it is not clear whether the SVM and SQI in desert soil are affected by climate and BSC in the temperature desert.
To evaluate the role and relative importance of climate and BSC on the soil MF, SQ, and SVM in interspaces of BSC patches in desert ecosystems, we collected 74 sites from the Gurbantunggut Desert. Furthermore, previous studies also found that the environment can significantly influence the growth, development, and distribution of BSC, as well as the physical and chemical properties and functions of soil. Thus, we hypothesized that 1) different types of BSCs have significantly different effects on soil MF, SVM, and SQ of soil in interspaces of BSC patches; 2) the environment can directly affect soil MF, SVM, and SQ and can also indirectly affect soil MF, SVM and SQ by altering BSC types and soil pH and EC.