Figure captions
Fig. 1 Variation in multifunctionality in the desert ecosystems. (a): Whole superficial soils (0-20 cm) and deep soils (20-100 cm); (b): vertical soil multifunctionality during the process of desertification; (c): multifunctionality in different desertification stages; (d) superficial and deep soil multifunctionality in different desertification stages. Significant differences between desertification sites were based on a one-way ANOVA followed by an LSD test. Linear least-squares regression relationships between multifunctionality and soil depth were estimated. The bold lines denote the least-squares linear regressions across soil depth, with their 95% confidence intervals (grey-shaded areas). S: slope; PD: potential desertification; MD: moderate desertification; SD: severe desertification.
Fig. 2 Variation in microbial alpha-diversity during desertification progression. Significant differences between desertification sites were based on a one-way ANOVA followed by an LSD test. Vertical variation in the Shannon and phylogenetic diversity indexes for bacterial, archaeal, and fungal communities was estimated via linear least-squares regression. The bold lines denote the least-squares linear regressions across soil depth, with their 95% confidence intervals (grey-shaded areas). S: slope; PD: potential desertification; MD: moderate desertification; SD: severe desertification.
Fig. 3 General patterns of microbial beta-diversity in superficial and deep soils during the process of desertification. NMDS showed the variation in the microbial community for soil bacteria (A), fungi (B), and archaea (C). 95% confidence ellipses are shown around the sites. Differences in beta-diversity among the bacteria, fungi, and archaea were estimated based on a Bray-Curtis distance matrix of all soil samples. Community similarity was calculated based on 1–[dissimilarity of the Bray-Curtis distance metric]. The lines denote the least-squares linear regressions across soil depth, with their 95% confidence intervals (grey-shaded areas). ***: P< 0.001. Significant differences of beta-diversity between desertification sites were based on a one-way ANOVA followed by an LSD test.
Fig. 4 Relationships between the dominant phyla of soil microbiomes and multifunctionality.
The red lines denote the least-squares linear regressions with their 95% confidence intervals (grey-shaded areas). S: slope.
Fig. 5 Relationships between microbial diversity and multifunctionality. The red lines denote the least-squares linear regressions with their 95% confidence intervals (grey-shaded areas). S: slope.
Fig. 6 Main predictors of soil multifunctionality in the desert ecosystems. The figure shows the random forest mean predictor importance (%increase in MSE) of soil variables and microbial community and diversity (Shannon and phylogenetic diversity indexes) for multifunctionality for all data sets. The abundances of standardized dominant phyla of soil bacteria (Chloroflexi and Acidobacteria), fungi (Ascomycota and Basidiomycota), and archaea (Thaumarchaeota and Euryarchaeota) were then averaged to obtain an overall microbial species index. These standardized diversity indexes (Shannon and phylogenetic diversity) of soil bacteria, fungi, and archaea were then averaged to obtain an overall biodiversity index. The significance levels of each predictor are as follows: *: P < 0.05; **: P< 0.01; ***: P < 0.001. EC: electrical conductivity.
Fig. 7 Direct and indirect effects of soil depth, pH, electrical conductivity (EC), bulk density (BD), microbial species index, and biodiversity index on multifunctionality. Structural equation models are shown for all data sets. Numbers adjacent to arrows are indicative of the effect size (bootstrap P value) of the relationship. R2 denotes the proportion of variance explained. Standardized total effects (direct plus indirect effects) derived from the structural equation models depicted above. The abundances of standardized dominant phyla of soil bacteria (Chloroflexi and Acidobacteria), fungi (Ascomycota and Basidiomycota), and archaea (Thaumarchaeota and Euryarchaeota) were then averaged to obtain an overall microbial species index. These standardized diversity indexes (Shannon and phylogenetic diversity) of soil bacteria, fungi, and archaea were then averaged to obtain an overall biodiversity index.