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.