Responses Of Castor Plant To Foreign Calcium Amendment At Seedling Stage Under Saline Soil Conditions

Castor bean (Ricinus communis L.) is one of the most important oil crops grown under diverse climatic conditions in the world. With the emerging importance of bioenergy, the castor bean is gaining new attention from agronomists and producers as a potential bioenergy crop for producing biodiesel. Although castor is found to have medium salt tolerance, the emergence and seedling establishment are very difficult when castor plants are grown in saline soil containing medium to high salt concentrations, leading to the failure of the establishment of high yield population. The study was conducted on the Experimental Farm and in Jiangsu Provincial Key Laboratory of Physiology of Yangzhou University from2009to2010. It consisted of three experiments, a germination experiment, a seedling experiment, and a pot experiment. In the germination test, the effects of foreign salinity and foreign calcium levels on the water uptake and germination of castor bean were studied. In the seedling experiment, seedlings were cultured in plastic seedling trays containing organic matter-soil mixture at different salinity and foreign calcium levels. The effects of salinity and foreign calcium amendment on the growth and physiological parameters and ion contents were studied. In the pot experiment, seedlings were transplanted into pots containing soils at the corresponding salinity levels. The effects of salinity on growth and physiological parameters and castor bean yield were studied. The main results were as follows.1. Water Uptake and Germination of Castor Seeds as Influenced by Salinity and Foreign Calcium AmendmentDuring the first7d of treatment, the germination rate of castor seeds was significantly reduced with the increase of salinity level in the solution culture. Foreign calcium amendment did not alleviate this inhibition. On the contrary, with the increased ion concentration in solution, castor seed the germination rate was even lower. However foreign calcium amendment made castor seed germinate in advance under saline conditions. Low-salt conditions increase the water absorption percentage of castor seeds, while high-salt conditions significantly reduce the water absorption percentage of castor seeds. Foreign calcium amendment did not improve the water absorption percentage of castor seeds, and with the increase of calcium concentration, the water absorption percentage of castor seeds decreased. The water absorption percentage process met the simulation curve of the logarithmic function, and the water absorption rate met the simulation curve of the exponential function.2. Growth and Physiological Parameters of Castor Seedlings as Influenced by Different Levels of Salinity and Foreign Calcium AmendmentWith the increased salinity level in seedling media, the emergence rate was significantly reduced. The amendment of foreign calcium significantly lessened the inhibitive effects produced by salinity stress. At0.3%salinity level, the growth of cotyledons and true leaves was significant slowed down; plant height, fresh dry weight, moisture content, and the contents of soluble protein and soluble sugar in true leaves were not significant affected; the contents of chlorophyll, free amino acids, proline, and MDA were increased significantly. The foreign calcium amendment of5-10mM significantly reduced the content of proline and MDA in leaves. At0.6%salinity levels plant height, cotyledon, true leaf, fresh weight, dry weight, moisture content, the contents of soluble protein, soluble sugar and chlorophyll were all significantly reduced. The free amino acids content and MDA increased significantly. The foreign calcium amendment of10-15mM significantly increased plant height, the growth of cotyledon and true leaves, fresh weight and dry weight, moisture content, the contents of soluble protein, soluble sugar, chlorophyll and free amino acids, and decreased the content of MDA.3. Ion absorption of Castor Seedlings as Influenced by Different Levels of Salinity and Foreign Calcium AmendmentAt the0.3%salinity level, the content of K+, Na+, Cu2+, and Fe3+in castor seedlings was significantly increased, while the content of Mg2+and the ratio of K+to Na+(K+/Na+) were significantly reduced; compared with the control, no significant differences were observed in the content of Ca2+, Mn3+, and Zn2+, but the ratios of these ions to Na+were significantly reduced; the ratios of Ca2+, Mn3+, and Zn2+to Na+were reduced at low concentrations of foreign calcium amendment and increased at high concentrations of foreign calcium amendment. At the0.6%salinity level, salinity stress reduced the content of K+, Ca2+, Mg2+and K+/Na+, but increased Na+content. The content of K+, Ca2+, and Mg2+was significantly increased when10mM foreign calcium amendment was applied to the seedling media. The15mM foreign calcium amendment significantly reduced Na+content and increased K+/Na+. Salinity stress increased the content of Cu2+, Fe3+, Mn3+and Zn2+. With the increase of foreign calcium amendment, the ratios of Cu2+, Fe3+, Mn3+and Zn2+to Na+were significantly increased.4. Growth and Physiological Parameters of Castor Bean Seedlings as Influenced by Salinity Stress after Seedling TransplantationCompared with the salinity level of0.3%, castor plants were more adaptable at the salinity level of0.3%. At the salinity level of0.6%, the growth of castor plant was significantly inhibited. Chlorophyll, soluble sugar, and MDA were most seriously affected at8/24. The seedlings treated by foreign calcium amendment at seedling stage were more adaptable than untreated seedlings. In this experiment, the physiological and growth parameters and the yield of castor plant treated with10mM foreign calcium amendment were better than other treatments.