* The significance of the difference between the two CO2 concentrations is given according to the Student’s t-test, with P
≤
0.05.
**
The significance of the difference between the two CO2concentrations is given according to the Student’s t-test, with P ≤ 0.01.
*** The significance of the difference between the two CO2concentrations is given according to the Student’s t-test, with P ≤ 0.001.2.11