Fig. 4: Relationship between soil pH and denitrification.
From: Intermediate soil acidification induces highest nitrous oxide emissions
Correlation between soil pH and potential denitrification activity (PDA) (a), and the N2O/(N2O + N2) product ratio of denitrification (b) across the Gannan alpine meadow, the Inner Mongolia steppe, and the Guyuan semi-arid grassland. Linear regression model with two-sided test was used for the statistical analysis. A second-order polynomial fit described the hump-shaped relationship between soil pH and PDA across the three field sites (a, PDA = −0.0334pH2 + 0.446 pH − 1.304). A linear regression was fitted between soil pH and N2O/(N2O + N2) ratio across the three field sites (b, N2O/(N2O + N2) = −0.082 pH + 1.265). Cyan, red, yellow, and blue lines represent correlations in Gannan (n = 20), Inner Mongolia (n = 20), Guyuan (n = 30), and all three sites (n = 70), respectively. The error bands (shaded areas) represent the 95% confidence intervals around best-fit regression line. Statistics (adjusted R2 and P values) for polynomial (a) and linear (b) regression are indicated. Source data are provided as a Source Data file.
