Table 1.
Soil characteristics and maize yields (averaged from 2009 to 2012) under application of N fertilizers at five rates.
Fig 1.
Concentrations of total microbial biomass (A), fungi (B) and bacteria (C), and ratios of fungi to bacteria (D) in three soils under application of N fertilizers at five rates (0, 168, 240, 270 and 312 kg N ha-1). Error bars indicate standard errors. Different letters within each soil indicate significant differences among N fertilization treatments.
Fig 2.
Concentrations of gram-positive (Gm+, A) and gram-negative bacteria (Gm–, B), ratios of Gm+ to Gm- (C), and concentrations of actinomycetes (D) in three soils under application of N fertilizers at five rates (0, 168, 240, 270 and 312 kg N ha-1). Error bars indicate standard errors. Different letters within each soil indicate significant differences among N fertilization treatments.
Fig 3.
The structural equation model showing the direct and indirect effects of soil type and N fertilization on fungi (A) and bacteria (B). Soil fertility index is a patent variable indicated by total N, C/N ratio, available N, P, and K. Bacteria is indicated by Gram-positive (Gm+) and Gram-negative (Gm–) bacteria. The width of arrow indicates the strength of the standardized path coefficient (*, P < 0.05; **, P < 0.01, ***, P < 0.001).
Fig 4.
Soil microbial community composition and environmental constraints.
A) Principal component analysis (PCA) of the phospholipid fatty acid (PLFA) data. Error bars indicate standard errors. The symbol size is positively correlated with N application rate. B) Redundancy analysis (RDA) of the PLFA data as explained by environmental variables. The explanatory variables followed by asterisks indicate significant influences on the PLFA data (*, P < 0.05; **, P < 0.01; ***, P < 0.001).