Fig. 3: Effects of soil pH on denitrifier community composition and N2O emissions.
From: Intermediate soil acidification induces highest nitrous oxide emissions
Denitrification gene ratios [(nirK+nirS)/nosZI ratio] (a–c) and N2O emissions (e–g) in soil with different pH due to acid treatment from the Gannan alpine meadow, the Inner Mongolia steppe and the Guyuan semi-arid grassland, and the relationship between soil pH and the (nirK+nirS)/nosZI ratio (d) and N2O emissions (h) across the three sites. Acid treatments correspond to A0, A1, A2, A3 and A4. A second-order polynomial fit described the hump-shaped relationship between soil pH and the (nirK+nirS)/nosZI ratio (d, (nirK+nirS)/nosZI = −0.072pH2 + 0.871 pH − 2.204) and N2O fluxes (h, N2O = −0.357pH2 + 4.273 pH − 9.560) across the three sites. In a–c and e–g one-way ANOVA with two-sided and post-doc test was conducted to determine significant differences. Different letters indicate a significant difference among acid addition treatment levels at P < 0.05. The box plots show the first and third quartiles (box limits), median (center line), and whiskers extend to a maximum of 1.5 times the interquartile range (IQR). For a, b, e, f, n = 4; c, g, n = 6. The error bands (shaded areas) in (d and h) represent the 95% confidence intervals around the best-fit regression line. Statistics (adjusted R2 and P values) for polynomial regression are indicated. The exact P values: P = 0.005 in a, e, P = 0.003 in b, P = 0.047 in c, P = 0.019 in f, and P < 0.001 in (g). Source data are provided as a Source Data file.
