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’.