3.3 Soil microbial diversity
The soil bacterial and fungal α-diversity index were differed among the
three groups (Fig. 4a, b, f, g ). Compared with Control,
petroleum pollution led to a significant reduction in soil bacterial
diversity (p <0.05). For fungi, soil fungal diversity had been
significantly reduced by petroleum pollution regardless of the
contamination duration. Moreover, correlations between microbial
diversity index and soil physicochemical properties had been calculated
(Fig. S3 ). The results showed that the Chao1 index was
negatively correlated with soil TPH and EC (p <0.05) for
bacteria. For fungi, the Chao1 index was negatively correlated with soil
EC (p <0.001). The PCoA analysis of microbial community
profiles proved that groups could separate soil bacterial and fungal
communities (Fig. 4c, d, h, i ). In addition, the results of
ANOSIM uncovered that the total discrepancy among groups was more
significant than within groups.
Through VPA analysis, the relative contributions of soil sampling points
and soil groups, soil physical and chemical properties and metals to the
composition of soil microbial community were revealed. The effects of
soil sampling sites and groups, soil physical and chemical properties,
metallomes and their interactions on the composition of soil microbial
community were analyzed. For bacterial community (Fig. 4e ),
these variables collectively explained 53% of observed discrepancies,
leaving 43% unexplained. Among those separate variables, soil physical
and chemical properties explained the most significant part of the
difference in bacterial community profiles (12%, p <0.05),
followed by soil metallome (8%, p <0.05), sampling location
and sampling group (7%, p <0.05). Their interactions
interpreted 36 percent of the total discrepancy in bacterial community
composition (p <0.05).
For fungal communities (Fig. 4j ), the same variable explained
60% of the observed discrepancies, and 40% of it was unexplained.
Among these independent variables, sampling sites and sampling groups
contributed the most to the change of fungal community composition
(11%, p <0.05), while soil physicochemical properties only
accounted for 6% of total variation (p <0.05). Interactions
between soil physicochemical properties and soil metallomes explained
13% of the discrepancies in fungal community profiles, while the
interactions between all variables explained 54% of the variation (p
<0.05).