The effects on the SOD activity in seedling leaves
Under different light intensities, the SOD content in the leaves of the six mangrove species showed significant differences (P< 0.01; Figure 3). The SOD activity in the leaves of theK. obovata , A. marina , R. stylosa , and B. sexangula seedlings showed a gradually decreasing trend, with the lowest activities under the G1 treatment. The SOD activity in the leaves of the A. corniculatum and C. tagal seedlings first decreased and then increased, with the lowest activities observed under the G2 treatment. These results indicate that too high or too low light intensity can increase the stress of the seedlings, leading to an increase in the SOD activity. However, when the light intensity is reduced to a certain extent, exceeding the tolerance range of the seedlings to low light stress, the SOD synthesis in seedlings is blocked, and the SOD activity is reduced.
Under different flooding times, the SOD content in the leaves of the six mangrove species all had significant differences (P < 0.01). The SOD activity in the leaves of the K. obovata , R. stylosa , and C. tagal seedlings first decreased, then increased, and finally decreased, with the lowest values observed under the T2 treatment. The SOD activity in the leaves of the A. marina andA. corniculatum seedlings first decreased and then increased, with the smallest values under the T3 treatment. The SOD activity in the leaves of the B. sexangula seedlings first increased and then decreased, with the smallest values under the T1 treatment. The above results demonstrate that too long or too short flooding times can increase the seedling stress.
Under different seawater salinities, the SOD content in the leaves of the six mangrove species showed significant differences (P< 0.01). The SOD activity in the leaves of the K. obovata seedlings showed a gradually decreasing trend, with the lowest values under the S1 treatment. The SOD activity in the leaves of theA. marina and R. stylosa seedlings showed an initially decreasing and then increasing trend; these seedlings received the least stress under the S2 treatment. The SOD activity in the leaves of theA. corniculatum seedlings showed a gradually increasing trend; these seedlings received the least stress under the S1 treatment. The SOD activity in the leaves of the C. tagal and the B. sexangula seedlings first increased and then decreased, with the smallest values observed under the S1 treatment. When the seawater salinity exceeded the tolerance range of the seedlings, the synthesis of SOD was blocked, and the SOD activity decreased rapidly.