Abstract
Soil bacterial communities are central to ecosystem functioning and services, yet spatial variations in their composition and diversity across biomes and climatic regions remain largely unknown. We employ multivariate general additive modeling of recent global soil bacterial datasets to elucidate dependencies of bacterial richness on key soil and climatic attributes. Although results support the well-known association between bacterial richness and soil pH, a hierarchy of novel covariates offers surprising new insights. Defining climatic soil water content explains both, the extent and connectivity of aqueous micro-habitats for bacterial diversity and soil pH, thus providing a better causal attribution. Results show that globally rare and abundant soil bacterial phylotypes exhibit different levels of dependency on environmental attributes. Surprisingly, the strong sensitivity of rare bacteria to certain environmental conditions improves their predictability relative to more abundant phylotypes that are often indifferent to variations in environmental drivers.
Highlights
Delineating biogeographical patterns of soil bacterial richness could offer insights into potential links between natural bacterial community traits and belowground ecological functioning[1]
Merging the geo-referenced 16S rRNA sequence data resulted in 844 valid soil samples, of which, 320 representative sampling sites were obtained after sample aggregation (Fig. 1a)
Incorporating the effects of soil and climate in the analysis of bacterial biogeography based on global datasets provides new insights into the key factors, namely climatic water content and pH that shape soil bacterial richness and community structure
Summary
Delineating biogeographical patterns of soil bacterial richness could offer insights into potential links between natural bacterial community traits and belowground ecological functioning[1]. The establishment of reliable global maps of bacterial biogeography hinge on inclusion of ample sampling locations and tackle the hurdles of uneven sample sizes and primer biases in meta-analyses[6]. To overcome these limitations towards development of unbiased estimates of global bacterial richness patterns, comprehensive and well-harmonized data sets are required. Three recently published datasets of soil bacterial community composition[17,20,21] combined with a consistent set of covariates (Supplementary Table S1) permit the (i) systematic consideration of composite soil and climate variables that could reflect salient conditions of soil bacterial habitats, and (ii) enable a process-based understanding of the hierarchy in environmental factors that control soil bacterial richness. We (iii) analyze biogeographic trends to statistically test the explanatory power of composite variables, climatic water content, with respect to soil bacterial richness and (iv) predict global biogeographic trends using general additive models (GAM) and tree-based methods
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