4 Combination of Elevated CO 2 Levels and Soil Contaminants’ Stress ... 75
4.2.8 Statistics
Data were expressed as means ± standard deviation ( n = 3; n represents three repli-
cate pots) and analyzed statistically using the SPSS software program (SPSS Inc.,
USA, version 16.0). The data were analyzed with a two-way analysis of variance
(ANOVA) approach, i.e., Cd or Cu treatment (three levels) and CO 2 treatment (two
levels). The mean values from the ambient plots were compared to the mean values
from the FACE plots on each day of measurement using Tukey’s test. The unilateral
t test was also performed to distinguish among enzyme activities. The difference
between the means was considered significant at p < 0.05.
4.3 Results and Discussion
4.3.1 Changes in Enzyme Activities
The changes in the activities of enzymes in the leaves of rice at mid-tillering growth
stage are shown in Figs. 4.1 and 4.2. In Cu treatment group, the activity of CAT in
leaves of rice grown on FACE plots with 50 and 400 mg kg−1 Cu in the soil was
41.9 and 40.0 % lower, respectively, than that in leaves of rice grown on ambient
plots (Fig. 4.1a). The activity of APX in leaves of rice grown on FACE plots with
400 mg kg−1 Cu was 18.9 % lower than that in leaves of rice grown on ambient
plots (Fig. 4.1b). The activity of POD in leaves of rice grown on FACE plots with 0
(control) mg kg−1 Cu added was 39.3 % higher than that in leaves of rice grown on
ambient plots, while no significant differences were found between the FACE and
ambient plots either 50 or 400 mg kg−1 Cu treatment group (Fig. 4.1c). The activity
of SOD in leaves of rice grown on FACE plots with 0 (control) mg kg−1 Cu was
30.9 % higher than that in leaves of rice grown on ambient plots. No significant dif-
ferences were found between the FACE and ambient plots either 50 or 400 mg kg−1
Cu treatment group (Fig. 4.1d). In Cd treatment group, the activity of CAT in leaves
of rice grown on FACE plots with 0.5 mg kg−1 Cd was 34.0 % lower than that in
leaves of rice grown on ambient plots (Fig. 4.2a). The activity of APX in leaves of
rice grown on FACE plots with 0.5 mg kg−1 Cd was 18.9 % lower than that in leaves
of rice grown on ambient plots (Fig. 4.2b). No significant differences on the activ-
ity of POD were found between the FACE and ambient plots in each Cd treatment
group (Fig. 4.2c). The activity of SOD in leaves of rice grown on FACE plots with
0 (control) mg kg−1 Cd added was 46.3 % higher than that in leaves of rice grown
on ambient plots, while that was 50.4 % lower in 0.5 mg kg−1 Cd treatment group
(Fig. 4.2d).
In Cu treatment groups, the changes in the activities of enzymes in the leaves of
wheat at mid-tillering and panicle-initiation growth stages are shown in Fig. 4.3.
No significant differences in CAT activities were found between the FACE and
ambient plots in each Cd treatment group at mid-tillering growth stage (Fig. 4.3a).