3.5 Diversity of soil bacteria and fungi
NT significantly increased soil bacterial diversity on average compared with CT (Fig. 5). Its diversity decreased with soil depth under NT. N application also significantly affected bacterial diversity under NT, whereas N application and soil depth had no effect under CT. NT had higher bacterial diversity than CT in the 0–10 cm layer. Bacterial diversity decreased with an increase in N application rates under NT in the 0–10 cm layer, while N application had no influence in the 10–25 cm layer. Similarly, NT significantly enhanced the average value of soil fungi diversity compared with CT (Fig. 6). Soil fungal diversity decreased as the soil depth and N application increased under NT. However, fungal diversity of CT was not influenced by soil depth and N application also had no influence on it in 10–25 cm layer.
Principal component analysis of bacterial composition at the phylum level showed that two principal components accounted for 47.7% and 42.4% of the overall variances among these treatments in the 0–10 cm and 10-25 cm layers, respectively (Fig. 7). We also found that PCoA of the fungal composition showed that two principal components accounted for 46.5% and 39.2%, respectively. We revealed that the two fractions (CT and NT) formed their clusters separated by PC1 in both layers. For fungi, the samples under the three N application rates of CT clustered closely, while samples within the NT differed more distinctly in the two layers.