3.2 Soil microbial community
The PLFA contents of the total and grouped soil microorganisms under tillage and N application treatments are shown in Fig. 3. All of the PLFA contents in the 0–10 cm layer were greater than in the 10–25 cm layer under NT, but the total PLFAs and bacterial PLFAs did not change with soil depth under CT. The average values of bacteria, fungi, and actinomycetes PLFAs were higher under NT than CT. In addition, only fungi and the F:B ratio were significantly affected by N level (Table S3). Overall, the total PLFAs were increased by 19.2% under NT compared with CT and not significantly affected by N level (Fig. 3a–b). For each grouped soil microorganism, bacterial PLFAs and actinomycetes PLFAs under NT were increased by 21.2% and 24.4%, respectively, compared with CT, but not significantly affected by N level at both depths (Fig. 3c–d and Fig. 3g–h). Fungal PLFAs also increased under NT compared with under CT. The fungal PLFAs of N2 was the highest than N1 and N3 under NT, while there was no effect of N application rate under CT in the 0–10 cm layer (Fig. 3e–f). Moreover, the G+:G- ratio was insignificantly affected by soil depth, tillage treatments, and N application rates (Table S3). The G+:G- ratio increased with increasing N application rates under NT and there was no effect of N application rate under CT at 0–10 cm (Fig. 3i–j). In addition, the F:B ratio was not significantly affected by tillage management. N2 produced a higher F:B ratio than the other two N levels under NT, whereas there was no effect of N application rate on F:B ratio under CT in both depths (Fig. 3k–l).