3.4. Linkages between soil CNP stoichiometry and enzyme stoichiometry
There was a negative linear correlation between enzyme C: N ratio and soil C: N ratio in 0-20 and 20-40 cm soil layers (p < 0.01), but a positive linear correlation in 40-60 cm soil layers (p < 0.05) (Fig. 3). Enzyme C: P ratio had a negative linear correlation with soil C: P ratio in 0-20 and 40-60 cm soil layers (p < 0.01), but a positive linear correlation in 20-40 cm soil layer (p< 0.01). Enzyme N: P ratio had a negative linear correlation with soil N: P ratio in 0-20 cm soil layer (p < 0.01), but a positive linear correlation in 20-40 and 40-60 cm soil layers (p < 0.01).
In AG (Fig. 4a), RDA analysis showed that enzyme activity (βG, NAG, and ACP) and enzyme stoichiometry (enzyme C: P and N: P ratio) were mainly associated with soil nutrient elements (TC, TN, TP, SOC, NH4+-N, NO3--N, and AP, positively) and soil stoichiometry (soil C: N and C: P ratio, negatively). Among them, TP and NH4+-N had significant effects on biological factors (p < 0.01), indicating that they were the main factors driving AG enzyme activity and enzyme stoichiometry variation. In WM (Fig. 4b), RDA analysis showed that enzyme activity (βG and NAG) and enzyme stoichiometry (enzyme C: P and N: P ratio) were mainly related to soil nutrient elements (TN, TP, SOC, NH4+-N, NO3--N, and AP, positively) and soil stoichiometry (soil C: N, C: P, and N:P ratio, negatively). Among them, TP and WSA (2-1 mm) had significant effects on biological factors (p < 0.01). In PC (Fig. 4c), RDA analysis showed that enzyme activity (βG, NAG, and ACP) and enzyme stoichiometry (enzyme C: P and N: P ratio) were mainly related to soil nutrient elements (TC, TN, TP, SOC, NH4+-N, NO3--N, and AP, positively) and soil stoichiometry (soil C:P and N:P ratio, positively). Among them, NO3--N had significant effects on biological factors (p < 0.01). Meanwhile, the enzyme C:P and N:P ratios were negatively associated with enzyme C:N ratios in all land use patterns.
4. Discussion