3.1 SOM mineralization response to artificial root exudates
The temporal patterns of CO2 emissions from all artificial root exudate–treated soils were similar. The CO2 efflux was highest at the beginning of the incubation (days 1–4), and exponentially decreased until day 15. Furthermore, it reached a stable level with only minor fluctuations until the end of the chasing period (Fig. 1a). Compared with the soil without additions (Control), the input of artificial root exudates led to an increase in cumulative CO2 emissions by 25%, 25%, 20%, and 19%, as CN6 > CN10 > CN80 > C-only, respectively (Fig 1b).
The input of root exudates with low C/N ratios (CN6 and CN10) significantly increased qCO2 on day 3. However, the qCO2 decreased from day 3 to day 45 in all treatments in the following order: CN6 > CN10 > CN80 > C-only > Control (Fig. 2a). In contrast, the CUE increased from day 3 to day 45 (Fig. 2b). The addition of artificial root exudates likewise decreased the CUE value in the following order: control > C-only > CN80 > CN10 > CN6.