Patterns of species richness and turnover rate along the
elevation gradients.
Our results suggest that PTEs, with the interaction of topographic
heterogeneity and climate change, have profoundly affected the
biodiversity trends around metal mines along the elevation gradients of
the Qilian Mountains. In the habitats classified as “natural” (i.e.,
not contaminated or lightly contaminated), the plant richness showed a
unimodal distribution with increasing elevation (Fig. 1a, explained
deviance = 38%, P < 0.005). Compared to the natural habitats,
the presence of PTEs in soil caused an increase in plant richness (Fig.
1a, explained deviance = 58%, P < 0.005) and a decrease in
plant evenness (Fig. 1b, explained deviance = 76%, P <
0.005). For the variations in plant richness, evenness, and cover, the
models involving Climate × PTEs or Topography × PTEs described the data
better than the models of climate, PTEs, or topography alone or the
models involving additive effects (Supplementary materials Tables 2, 3,
4). Nevertheless, the deposition of PTEs in the soil altered the plant
diversity distribution unevenly along the elevation gradient. Compared
to the natural habitats, the plant species richness in PTE-polluted
habitats located in the low-elevation desert (1578-2183 m a.s.l) and
lowland grassland (2365-3079 m a.s.l) showed significant changes, with
maximum increases of 25% and 18%, respectively. However, the evenness
in the PTE-polluted habitats in the same elevation zone decreased by
44% and 45%, respectively (Fig. 1b and Supplementary Materials Fig.
7). Unlike the obvious changes in plant richness between the natural
habitats and PTE-polluted habitats, the change in plant coverage between
these two areas was relatively small (Fig. 1c, explained deviance =
95%, P < 0.005).
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Place Fig 1 here
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Alongside changes in species richness, the species composition of plant
communities changed with the presence of PTEs and the interaction of
topographic heterogeneity and climate change. Nonmetric multidimensional
scaling (NMDS) demonstrated the spatial changes in plant communities
shaped by PTE deposition in different study sites (n = 64) of the
mountain range (average turnover rate = 0.51, range = 0.16 - 1.00) (Fig.
1d). The turnover rate reflected the high similarity in the plant
composition at the mine sites on the same elevation gradient (PERMANOVA,
R2 = 47%, P = 0.01). The results showed that PTE
deposition changed the plant species composition of PTE-polluted
habitats in most classified groups compared with that in the natural
habitats (F = 9.06, df = 2696, P = 0.027, Fig. 1d). Throughout the four
studied climate zones along the elevation gradient (mountain desert
steppe, mountain grasslands, desert grassland, and mountain
shrub-steppe), we found that the turnover rates in the PTE-polluted
habitats showed greater changes in plant composition in the
low-elevation mountain desert steppe (ANOVA, P = 0.052) and mountain
grassland (ANOVA, P < 0.01) (Fig. 2).
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Place Fig 2 here
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