The relationship between CH4 uptake and N2O emission in a semiarid temperate steppe in Inner Mongolia with N addition. The relationship between N addition and the logarithmic ratio of CH4 uptake and N2O emission changed across 3 experimental years (2013–2015). We introduced a relaxation variable to ensure positive values for both the numerator and denominator, thereby facilitating the analysis of the relationship between the ratios. (a) The vertical line and dotted line depict the neutral threshold (4 g N m−2 y−1) at which the coupling relationship transformed, following nonlinearly curve fitting, the antagonistic relationship was illustrated and magnified in (b and c); the area to the left of the vertical line, as indicated in (a), showed a synergistic relationship in (c). (d) Two points, N = 4 and N = 64, were selected to calculate the incremental change in the rate of CR.
