3.2 Responses of enzymes activity and microbial biomass to artificial root exudates
Compared with the control, the activities of the three enzymes measured significantly increased. The BG and XYL enzymes increased in the order C-only > CN80 > CN10 > CN6 > Control (Fig. 3). Conversely, NAG activity decreased with decreasing N content in the simulated root exudates on day 3, following the order of CN 6 > CN10 > CN80 > C-only. Increasing the BG/NAG ratio increased qCO2(R2 = 0.41, P = 0.01) and suppressed the CUE (R2 = 0.36, P = 0.02) (Fig. 4a). Compared with the control, MBC and MBN remarkably increased (except in CN6 and C-only). However, there was a minor rise from day 3 to day 45 in all treatments (Table S2). C/N ratios of the microbial biomass ranged from 3.2 to 7.8 (Fig. 4c). The MBC/MBN ratio was negatively correlated with qCO2 (R2 = 0.29, P = 0.01) and CUE (R2 = 0.36, P = 0.02) (Fig. 4b).