Abstract
Changes in species composition across communities, i.e., β-diversity, is a central focus of ecology. Compared to macroorganisms, the β-diversity of soil microbes and its drivers are less studied. Whether the determinants of soil microbial β-diversity are consistent between soil depths and between abundant and rare microorganisms remains controversial. Here, using the 16S-rRNA of soil bacteria and archaea sampled at different soil depths (0–10 and 30–50 cm) from 32 sites along an aridity gradient of 1500 km in the temperate grasslands in northern China, we compared the effects of deterministic and stochastic processes on the taxonomic and phylogenetic β-diversity of soil microbes. Using variation partitioning and null models, we found that the taxonomic β-diversity of the overall bacterial communities was more strongly determined by deterministic processes in both soil layers (the explanatory power of environmental distance in topsoil: 25.4%; subsoil: 47.4%), while their phylogenetic counterpart was more strongly determined by stochastic processes (the explanatory power of spatial distance in topsoil: 42.1; subsoil 24.7%). However, in terms of abundance, both the taxonomic and phylogenetic β-diversity of the abundant bacteria in both soil layers was more strongly determined by deterministic processes, while those of rare bacteria were more strongly determined by stochastic processes. In comparison with bacteria, both the taxonomic and phylogenetic β-diversity of the overall abundant and rare archaea were strongly determined by deterministic processes. Among the variables representing deterministic processes, contemporary and historical climate and aboveground vegetation dominated the microbial β-diversity of the overall and abundant microbes of both domains in topsoils, but soil geochemistry dominated in subsoils. This study presents a comprehensive understanding on the β-diversity of soil microbial communities in the temperate grasslands in northern China. Our findings highlight the importance of soil depth, phylogenetic turnover, and species abundance in the assembly processes of soil microbial communities.
Highlights
Changes in community species composition across space (i.e., β-diversity) is a central focus of ecology and is vital for understanding community assembly processes [1,2]
The slopes of the distance–decay curves across spatial and environmental distances indicate the relative importance of spatial and environmental distances, and we found that the phylogenetic β-diversity for the bacterial communities in the topsoils was more strongly associated with spatial distance, while the taxonomic β-diversity in the subsoils was more strongly associated with environmental distance (Figure 2c,f)
These results suggest that both bacterial taxonomic β-diversity and archaeal β-diversity in both soil layers tend to be determined by deterministic processes, supporting our first hypothesis
Summary
Changes in community species composition across space (i.e., β-diversity) is a central focus of ecology and is vital for understanding community assembly processes [1,2]. Evaluating the relative contributions of deterministic and stochastic processes is critical for understanding the mechanisms of microbial community assembly but remains a challenge in current studies. Several statistical approaches have been developed to examine the relative importance of deterministic and stochastic processes, among which the distance–decay relationship (DDR) have been widely used [13]. This method evaluates the changes in the community composition along spatial and environmental gradients [14]. Null models have been used to infer ecological stochasticity by comparing the observed patterns with the expected random patterns produced by null models [6,16]
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