Researches Of Physiological Characteristics Of Coconut Seedling With The Replacement Of Potassium By Sodium

In the condition of which the total concentration of potassium and sodium was4mmol/L, a test with a major coconut cultivar (Hainan Tall) was carried out under the sand culture in the replacement of potassium by sodium. Some indicators were studied under the condition of the different proportional replacement of potassium by sodium, such as changes of sucrose and related metabolic enzymes activity, photosynthetic pigments, malonaldehyde, soluble saccharide, nutrient elements in the coconut leaves. The result showed that:1. Compared to the control, the contents of chlorophyll a, chlorophyll b, total chlorophyll were not affected when the proportional replacement of potassium by sodium was lower than50%, even increased, and decreased obviously in50%and75%, reduced slightly in100%. The tendency of changes of the ratios of chlorophyll a/b in all treatments was not only nearly alike and gradually steady, but also the difference between them was not significant (P>0.01). It showed that the stacked degree of the thylakoid membrane and its stability kept steady in the low proportion of replacement of potassium by sodium, which had no effect on, even enhanced energetic metabolism of photosynthesis in coconut leaves.2. As time goes on, the contents of malonaldehyde was equal to the control and steady in the treatments of25%,50%replacement of potassium by sodium; however rose in75%and100%, which was adverse to the growth of the plants in the long run. It displayed that membrane lipid peroxidation was not caused in coconut leaves in the low proportion of replacement of potassium by sodium. As a result, the membrane kept steady.3. The changes of the content of sucrose and soluble saccharide, as well as the activity of sucrose synthase and sucrose phosphate synthase, were similar to the control below the treatments of25%and50%replacement of potassium by sodium; not only the tendency was gradually steady and but also the difference between them was not significant in the later period(P>0.01). However, compared to the control, the contents of sucrose and soluble saccharide and the activity of sucrose synthase reduced gradually in the treatments of75%and100%replacement of potassium by sodium, except that the changes of the activity of sucrose phosphate synthase were as similar as the control. The results of the study expound that the low proportion of replacement of potassium by sodium had no effect on the contents of sucrose and soluble sugar and the activity of related enzymes in coconut seedlings, which provides stable carbon sources for carbon metabolism, so as to ensure the normal growth of plants.4. The nitrate reductase activity was equivalent to or higher than the control, as well as steady, when the proportion of replacement of potassium by sodium was lower than75%. However, the nitrate reductase activity decreased significantly in the excess of75%replacement of potassium by sodium. The result showed that the nitrate reductase activity was not affected, even improved in coconut leaves in the low proportion of replacement of potassium by sodium, so that the ability of nitrogen assimilation was kept or enhanced.5. As time goes on, Na+contents increased gradually in all treatments, which were2.03-2.80times than the control respectively after80days. Less than75%, K+contents added gradually that were only slightly lower than the control and was not significant (P>0.01)between the treatments after80days, however, K+contents declined gradually in the100%treatment, which were lower than the other treatments with a significant level(P<0.01). Nitrogen contents increased gradually in all treatments over time, but more than50%replacement of potassium by sodium in which the nitrogen contents were significantly lower than the control in the later period displayed a slow growth. Phosphorus contents increased gradually in all treatments over time, too; differently, phosphorus contents were significantly lower than the control in the later period in only75%replacement of potassium by sodium which showed a slow growth, too. Ca2+and Mg2+contents increased gradually in all treatments over time, compared to the control, in which the difference was not significant. Except that Mg2+contents were significantly lower than the control in the later period in only75%replacement of potassium by sodium which showed a slow growth. It indicated that mineral element assimilation in coconut leaves was not affect in the low proportion of replacement of potassium by sodium.