Researches Of Physiological Characteristics Of Cocos Irrigated With Seawater

Using seedlings of'Hainan Tall'and'Wenye2'coconut cultivars as the experimental materials, several physiological indices were comparatively studied, such as the leaves relative water content(LRWC), malondialdehyde(MDA), proline(Pro), soluble sugar(SS), chlorophyll content, rapid light curve under short-term(15d) and long-term(90d) seawater irrigation. The extended leaves numbers and inorganic cation after90d seawater irrigation in different concentrations seawater were also analysed. The results showed that the above physiological indexes rose bovious with the increase of seawater concentration and slat stress time.LRWC of the seedlings decreased much more in long-term seawater irrigation than in short-term, especially in high seawater concentration. Compared with Hainan Tall, Wenye2showed lower LRWC decline in low seawater concentration and higher LRWC decline in high seawater concentration, which indicated Wenye2was the more suitable variety cultivated in low salt environment.The variation trend of MDA was every complex. MDA content rose first and then drop in short-term seawater stress. However, it increased at first,decreased then and increased again sharply in long-term seawater irrigation. The decline of MDA under midterm seawater concentration indicated that Coconut may had regulation mechanism to reduce salt stress damage at this step. The sharp increase of MDA illustrated Coconutt membrane structure had been greatly damaged. There was no obvious differences between two cultivars.Pro and SS content of Coconut in the short term and the long term seawater stress rose significantly with the increased seawater concentration.Howver the increment of Pro and SS in long-term seawater stress were significantly greater than in short-term seawater stress, especially high seawater concentration treatment. The content of the two parameters under low seawater concentration had no notable variation, no matter in short term or long term seawater stress. Osmotic regulation was the main mechanism in high salt stress, but not in low. The change trend of Pro and SS content were very close in two cultivars.The three physiological parameters of chlorophyll content, Fv/Fm x ETR factor/2(maximum quantum yield of PSII with a saturated pulse after dark adaptation), Fv/Fm (maximum quantum yield of PSII) had similar change trends, which had on changes or slight drops with increased seawater concentration in short term seawater treatment. In long term seawater treatment, there were also no obvious changes in low salinity condition, however, the three indexes dropped sharply in high sality conditons. rETRmax (max-imum relative electron transport rate) declined persitently in salt stress, and greater in long term salt stress treatment than in short-term, especially in high seawater concentration. These results indicated that photosynthesis of coconut was inhibited more and more as the rise of salinity and the extension of time. The reduction of photosynthesis may attibute to part decomposition of chlorophyll and inhibition of enzyme activity participated in photosynthesis in short-term seawater irrigation or in long-term low seawater concentration irrigation. High concentration seawater in long term irrigation may lead to large decomposition of chlorophyll and degeneration inactivation of enzyme activity participated in photosynthesis. Finally, the photosynthetic capacity decreased sharply.Na+and C1-contents in coconut roots increased significantly greater than in leaves since low seawater concentration treatment. These two inorganic ions increased quickly in the roots from20%seawater irrigation, however, they rose gradually in leaves in the whole seawater irrigation process. K+content increased at low seawater levels and decreased at high levels in the roots.,but declined gradually in leaves. The whole K+content in the rootss and in leaves still reached a relatively high level. B oth K+/Na+in roots and in leaves kept high level treated by low seawater, only a rapidly decline colud be observed when treated by high concentration seawater. Ca2+content decreased with the salinity in roots, but increased in leaves. Mg2+content increased with the seawater concentration both in roots and in leaves. These results showed that, salt stress, coconut don't limit sodium chloride into the roots, but restrict these salinity to transport to the ground of the plant to adapt to the salt environment, The variaty of Ca2+that Ca2+may played an important role in this process. Limited to the ground of the department of transportation sodium chloride played an important role in the process. Change trends of K+/Na+, Na+, K+, Ca2+illustrated coconut made use of ions regulation to adapte in low salt environment.