2.4 Statistical analysis

The generalized linear model (GLM) multivariate procedure from SPSS software (Ver22, IBM, Armonk, NY, USA) was used for the ANOVA to test the effects among the treatments. The CO2 level, N supply rate and tissue type were defined as independent factors, and their full interactions were analyzed using the GLM procedure. Significance level was set at (p ≤0.05) for post-hoc test. Data presented in figures and tables were the average ± standard deviation.