Introduction
Soil biodiversity drives complicated ecological processes and plays a crucial role in exerting ecosystem functions and the provision of ecosystem services (Nielsen et al., 2012; Wagg et al., 2014; Geisen et al., 2018). The composition of soil animal communities thus strongly influences ecosystem multifunctionality (Wagg et al., 2014). For instance, soil animal communities may alter microbial activity, litter decomposition, nutrient mineralization, soil respiration, and plant community composition (Bradford et al., 2002; De Deyn et al., 2003; Eisenhauer et al., 2012; Johnston & Sibly, 2018). Consequently, shifts in soil animal community composition could dramatically influence the functioning and stability of terrestrial ecosystems (Sjursen et al., 2005; Suttle et al., 2007; Briones et al., 2009; Eisenhauer et al., 2014; Handa et al., 2014). Yet, little is known about the spatial and environmental factors that shape soil animal communities on a regional and global scale (Johnston & Sibly, 2020). To understand the ecosystem functioning and the mechanism of community composition evolvement, it is necessary to identify the factors that shape the distribution and structure of various soil faunas (Crowther et al., 2019).
Species turnover pattern (or beta diversity) is a basic pattern in biogeography and macroecology (Gaston, 2000), and it provides fundamental insights into mechanisms of community assembly, especially on a large scale (Anderson et al., 2011; Lafage et al., 2015). However, species turnover patterns have received less attention than alpha diversity (Lennon et al., 2001), and measures of species turnover in previous studies usually based on single method (Gao et al., 2021). Utilizing different methods to measure the species turnover rates can better avoid the error caused by methods of measurement. Meanwhile, most studies on species turnover have been conducted locally (Kraft et al., 2011; Sasaki & Yoshihara, 2013). A few studies did investigate species turnover on large geographic scales, but they mostly focused on plants and animals. For example, recent studies have demonstrated that dispersal abilities were a key factor for both woody plants and birds in species turnover spatially (Chen et al., 2016; Sreekar et al., 2020). The global biogeography of soil animals has begun to gain attention only recently (Caruso et al., 2005; Dunn et al., 2009; van den Hoogen et al., 2019; Medini et al., 2021). Most of these studies focused on specific soil animal communities. For example, previous studies showed that earthworm community composition is determined by the mobility of the organisms (Medini et al., 2021), oribatid mite by spatial factors (Caruso et al., 2005), termites of Hymenoptera by temperature and precipitation (Dunn et al., 2009), and nematodes by temperature (van den Hoogen et al., 2019). Despite our accumulated knowledge about biogeographic patterns of soil biota, the underlying mechanisms of the distribution patterns remain unexplored (Xu et al., 2020). Particularly, the studies on the patterns of comprehensive taxa species turnover across latitudes are limited.
Environmental filtration and spatial processes have been associated with variations in ecological communities and biodiversity. However, their significance on multiple dimensions of beta diversity has not been fully explored in soil fauna (Li et al., 2020). Several research studies indicated that species coexistence was attributed to different environmental factors, such as habitat heterogeneity (Li et al.,2017), temperatures in different climates (Oliver et al., 2009), and soil nutrients (John et al., 2007). These factors provided species with different resources, time, and space to achieve coexistence as implied by the niche theory (Jia et al., 2015; Escudero & Valladares, 2016). Alternatively, neutral processes stated that species coexistence was resulted from biogeographic barriers and low dispersal abilities (Hubbell, 2001; Jia et al., 2015). Though two different theories, the niche theory and neutral processes actually jointly explained the coexistence of soil animal communities. They just have different roles on corresponding spatial scales (Gao et al., 2014). The underlying environmental controls that shape latitudinal shifts in soil animal communities on a global scale, however, have not been identified (Johnston & Sibly, 2020), especially the mechanisms. Therefore, our study aimed at addressing this knowledge gap and explored the influence of spatial and environmental factors on soil animal species composition across globally distributed sites by synthesizing data of comprehensive taxa of soil animal communities.
The objectives of the current study were: (1) to obtain an integrated analysis of the similarity of soil animal species composition along the latitude in East Asia, (2) to identify the patterns of species turnover along the latitude using two measures of species turnover, and (3) to assess the relative influence of environmental and neutral processes on species turnover of overall and functional forms of soil animals.