2.4. Statistical analysis
Soil C: N, C: P, and N: P were calculated by formula (1) (2) (3).
\(Soil\ C:N\ ratio=TC\div TN\)(1)
\(Soil\ C:P\ ratio=TC\div TP\)(2)
\(Soil\ N:P\ ratio=TN\div TP\)(3)
Enzyme C: N, C: P, and N: P were calculated by formula (4) (5) (6).
\(Enzyme\ C:N\ ratio=\ln\text{βG}\div\ln\text{NAG}\)(4)
\(Enzyme\ C:P\ ratio=\ln\text{βG}\div\ln\text{AP}\)(5)
\(Enzyme\ N:P\ ratio=\ln\text{NAG}\div\ln\text{AP}\)(6)
The vector analysis of enzyme activity is used to test the relative nutrient limitation. The relatively long vector length indicates the greater carbon limitation of soil microorganism, and the vector angle < 45° or > 45° indicates the relative degree of N or P limitation of soil microorganism, respectively. The vector length (VL) and vector angle (VA) are calculated by formula (7) (8) (Bai et al., 2021).
\(VL=\left[\left(Enzyme\ C:N\ ratio\right)^{2}+\left(Enzyme\ C:P\ ratio\right)^{2}\right]^{\frac{1}{2}}\)(7)
\(VA=Degrees\left\{ATAN2\left[\left(Enzyme\ C:P\ ratio\right),\left(Enzyme\ C:N\ ratio\right)\right]\right\}\)(8)
Excel 2016 was used for data processing, SPSS 23 was used for one-way ANOVA and LSD significance test (α = 0.05), and origin 2018 was used for chart drawing. Redundancy analysis (RDA) was used to analyze how enzyme activity and enzyme stoichiometry changed with soil physicochemical properties and soil stoichiometry, and the significance of these factors was tested by Monte Carlo permutation (permutation = 499). RDA analysis charts were drawn by Canoco 5.0 software.