2.3 CO2 efflux measurement
Gas samples (15 mL) were collected from 500-mL anaerobic bottles every
day using a 20-mL syringe before exudate solutions were injected into
the soil samples. Subsequently, the serum bottles were flushed with
artificial air for another 10 min and then sealed using a rubber
stopper. CO2 concentration was measured using a gas
chromatograph equipped with a thermal conductivity detector (Agilent
7890A, Agilent Technologies, Alto Palo, California, USA).