2.7 Statistical analysis
One-way analysis of variance (ANOVA) was used to evaluate the effects of
land-use type, seasonal change and soil depth on soil physiochemical
properties, α-diversity and the relative abundances of bacterial phyla
in SPSS 19.0 (SPSS, Chicago, IL, USA). While the interacted effects of
land-use, seasonal change and soil depth on soil physiochemical
properties were assessed by PerMANOVA (permutations = 999). The effects
of land-use, seasonal change and soil depth on overall bacterium
community dissimilarity were performed using ‘adonis’ and ‘anosim’
function within ‘vegan’ package in R 3.5.3.
Canonical correspondence analysis (CCA) was performed to identify the
major factors driving bacterial distribution in maize field between two
seasons as well as in two different land uses in spring and autumn. Soil
factors including soil moisture, SOM, TC, DOC, DON, C/N ratio, pH,
NO3-_N, and
NH4+_N were included in the analysis,
while TN was eliminated as strong collinearity in the CCA. Permutation
tests were applied to assess the significance of the partial effects of
the factors.
The relative abundance of bacterial orders (> 0.1%) was
analyzed in Statistical Analysis of Metagenomic Profiles (STAMP)
software, where Welch’s t-test was applied to compare the relative
abundance of bacterial orders between maize field and woodland in spring
and autumn, respectively. In addition, the heat-map of relative
abundance of bacterial community at order level was demonstrated using
the R package ‘pheatmap’ and ‘ggplot2’.