3.1 Effect of fertilization strategies on microbial communities
along the paddy soil profile
The absolute abundance of total and specific microbial groups (G−, G+
bacteria, actinomycetes, and fungi) in all treatments significantly
decreased with soil depth (Table 1, P <0.05). The
abundance of total and specific PLFAs were the lowest and highest in the
control and NPK + OM treatments, respectively, at the 0−40 cm soil
depth. Compared with that in the NPK treatments, NPK + ST showed
significantly higher bacterial (G−, G+, and actinomycetes) and fungal
abundance at the 10−20 cm soil depth (P <0.05). The
fungi to bacteria, G+ bacteria to actinomycetes, and fungi to G−
bacteria ratios gradually decreased with soil depth in all treatments
between 0 and 30 cm. The G+ to G−bacteria ratio increased with soil
depth for all treatments (Figure 1).
Both mineral and organic fertilizers significantly increased the G+ to
G− bacteria and actinomycetes ratios compared with those in the control
group at 0–30 cm soil depths (Figures 1b and c,P <0.05). NPK + ST showed the lowest fungi to bacteria
and G− bacteria ratios at 0–10 cm compared with those in the other
treatments (Figures 1a and d, P <0.05). At 10−40 cm, the
fertilized treatments showed higher fungi to bacteria and G− bacteria
ratios compared to those of the control.
There was no uniform pattern throughout the soil profile regarding the
influence of organic fertilizers on microbial functional PLFA ratios.
With equal amounts of fertilizer input, compared with NPK, NPK + OM
further stimulated more G+ bacteria than G− bacteria and actinomycetes
at all depths (Figures 1b and c). Soil respiration rates gradually
decreased with soil depth and the lowest values for each soil depth were
observed in the control (Figure 2a, P <0.05). NPK + ST
significantly increased the soil respiration rate at 0−20 cm
(P <0.05). NPK + OM showed a constant soil
qCO2 between the 0 and 40 cm soil depths, while both the
NPK treatments and the control significantly increased the
qCO2 values with soil depth. NPK + ST treatment showed
the lowest qCO2 at 10–20 cm compared to that at other
depths (Figure 2b, P <0.05).