The effects on the CAT activity in the leaves
Under different light intensities, the CAT content in the leaves of the six mangrove species showed significant differences (P< 0.01; Figure 4). The CAT activity in the leaves of theK. obovata , A. marina , and the R. stylosa seedlings showed a gradually decreasing trend, with the least low light stress under the G1 treatment. The CAT activity in the leaves of the A. corniculatum , C. tagal , and theB. sexangula seedlings decreased first and then increased, with the least low light stress under the G2 treatment. These results indicate that too high or too low light intensity can increase the low light stress of the seedlings, leading to an increase in CAT activity. However, when the light intensity is reduced to a certain level, exceeding the tolerance range of the seedlings to low light stress, CAT synthesis in seedlings is blocked, and CAT activity is reduced.
Under different flooding times, the CAT content in the leaves of the six mangrove species all showed significant differences (P< 0.01). The CAT activity in the leaves of the K. obovata and C. tagal seedlings first decreased, then increased, and finally decreased, with the least stress under the T2 treatment. The CAT activity in the leaves of the A. marina and A.corniculatum seedings first decreased and then increased, with the least stress under the T3 treatment. The CAT activity in the leaves of R. stylosa and B. sexangula seedlings first increased and then decreased, and the stress on the seedlings was the lowest under the T1 treatment. These results indicate that too long or too short flooding time can lead to an increase in the stress of the seedlings, and the CAT activity in the leaves increases. However, when the flooding time exceeds the tolerance range of the seedlings, the CAT synthesis is blocked, and the CAT activity decreases rapidly.
Under different seawater salinities, the CAT content in the leaves of the six mangrove species showed significant differences (P< 0.01). The CAT activity in the leaves of the K. obovata seedlings exhibited a gradually decreasing trend, and the stress of the seedlings was the lowest under the S1 treatment. The CAT activity in the leaves of A. marina seedlings first decreased and then increased, and the stress on the seedlings was the lowest under the S2 treatment. The CAT activity in the leaves of A.corniculatum seedlings showed a gradually increasing trend, and the stress on the seedlings was the lowest under the S1 treatment. The CAT activity in the leaves of the R. stylosa , C. tagal , and the B. sexangula seedlings first increased and then decreased, and the seedlings had the lowest stress under the S1 treatment. The above results indicate that too high or too low seawater salinity can promote the increase in CAT activity; however, when the seawater salinity exceeds the tolerance range of the seedlings, CAT synthesis is blocked, and CAT activity appears to decrease rapidly.