Introduction
Desert is the largest terrestrial ecosystem on earth, which is sensitive to human activity and climatic change (Laity, 2009). The common features of desert, such as extreme drought, strong ultraviolet radiation, and dramatic temperature fluctuations, limit the survival of plants and animals in this extreme environment (Sul et al., 2013). Thus, microorganisms become the dominant component of the desert ecosystem (Pointing et al., 2012).
The different desert habitats shaped the diverse microorganism colonization. Cyanobacteria showed the highest abundance in the biological soil crusts of deserts (Nagy et al., 2005; Zhang et al., 2016a; Arocha-Garza et al., 2017; Mogul et al., 2017; Sun et al., 2018). Actinobacteria was the dominant bacteria in the hyper-arid core in the Atacama Desert (Crits-Christoph et al., 2013). Many previous studies focused on the microbial community composition and assembly in the desert. However, there is no consensus of opinions about which environment factor is the main driver for the microbial community assembly on deserts. For example, Zhang et al. (2019) found that salinity was the key determinant of microbial community assembly in the Gurbantunggut Desert. Crits-Christoph et al. (2013) emphasized that water and salt contents were the main factors shaping soil microbiome in the Atacama Desert. Several previous studies indicated that moisture influenced the microbial community structures, assembly, and colonization of the Namib Desert (Warren-Rhodes et al., 2013; Stomeo et al., 2013; Valverde et al., 2015). Additionally, the results from the Namib Desert showed that soil chemistry and stochasticity affected the bacterial community assembly and xeric stress adjusted the variations of community function (Scola et al., 2018). The inconsistent responses probably came from the environmental heterogeneity of different deserts.
The Taklimakan Desert is about 1130 kilometers long from east to west, 400 kilometers wide from north to south, covering an area of 337,600 Km2. The terrain is high in the southwest and low in the northeast, with altitudes ranging from 780 m to 1500 m. The detailed microbial ecology of the Taklimakan Desert has been poorly investigated to date. An et al. (2013) investigated the bacterial diversity at the edge of the Taklimakan Desert. Yu et al. (2015) isolated 52 ionizing radiation-tolerant bacteria strains from this desert. Several prior studies identified some novel cultivable bacteria in the Taklimakan Desert (Zhang et al., 2010; Liu et al., 2010; An et al., 2010; Liu et al., 2011). Therefore, a comprehensive investigation is necessary for the taxonomic diversity of bacterial communities in the Taklimakan Desert.
The altitudinal gradient is considered a natural test to evaluate the response of the microbial community to environmental change (Körner, 2007; Siles and Margesin, 2017). Previous studies indicated that the altitudinal gradient might lead to different effects on microbial community population and composition in different ecosystems (Manzoni et al., 2012; Serna-Chavez et al., 2013). The large altitude scales might involve different climatic regions, which is complex to investigate the correlation of microbial community along the altitudinal gradient (Ren et al., 2018). Thus, it may be easier to understand the correlation between altitude gradient and microbial community composition on the same climate conditions. Understanding the response of altitude gradient to the microbial community was important for better understanding the adaptability of microorganisms in the desert ecosystem.
The aims of the present study were to (1) evaluate the variations of physicochemical properties and bacterial communities in the sand of the Taklimakan Desert, (2) reveal how altitude and sand property influence the structure of bacterial communities, and (3) understand the specificity and adaptation of bacterial communities in the Taklimakan Desert.