Response Characteristics Of Six Clonal Varieties Of Morus Alba L.To Salt Stress

In this study, The one-year-old seedlings of six clonal varieties of Morus alba L.were tested to study their responses to salt stress. In order to understand their salt tolerance mechanisms, their physiological and biochemical responses to salt stress were studied. As randomized complete block experiment was designed, 0% (CK), 0.2%, 0.3%, 0.4% four different gradients of soil salinity levels were prepared and the measurants were made on June 12, June 19, June 26, July 3 and July 10. The samples were taken to study their responses such as symptom formation, cell conductance, MDA, Pro, soluble protein, soluble sugar, SOD, POD, Chlorophy contents and etc. After destruction of sampling, Na ⁺, K ⁺, Cl^- contents and root activity were measured. Comprehensive analysis has been made for these characters in order to reveal the internal mechanisms. The main results are as follows.In order to get the required three salt gradients of the soil salt contents, pre-tests were conducted. Determined by simulation of the soil of salt contents preparation test: 0.3% salt water irrigating soil obtained 0.206% soil salinity; 0.45% salt water irrigating soil obtained 0.318% soil salinity; 0.7% salt water irrigating soil obtained 0.416% soil salinity. In order to ensure continuity of the test, it is rough measured salt content directly using wet soil, and test results showed that there was a little difference between the natural dried soil and wet soil from salt pond.In the early salt stress,the first to show the symptoms of salt stress is Guisangyou 12. With salt stress increased and the extension of time, the symptoms of salt stress has become increasingly obvious and serious . The salt stress symptoms of six clonal varieties of mulberry, can more intuitive reflect the difference of salt tolerance:Lucha1>Nongsang12>Anglv1> Husang32>Changsheng>Guisangyou12.With the increase of salt treatment,Cell membrane permeability and MDA of seedlings of mulberry was significantly increased, and chlorophyll decomposition accelerated, and root activity and net photosynthetic rate declined. For most of those clonal varieties, the dynamic changes in SOD, POD, Pro, soluble sugar and soluble protein did not appear in a similar trend.Six clonal varieties of Morus alba L. could adapt salt stress by increasing the content of Pro. In the high concentration of salt stress, proline content of six clonal varieties was significantly increased.It indicated that mulberry can produce free proline in order to improve the adaptability to salt stress.Net photosynthetic rate(Pn), stomatal conductance(Gs), transpiration rate(Tr)decreased with the salt stress increacing,and intercellular CO₂ concentrations(Ci)improved. It denoted the main factor inhibiting Pn is non-stomatal control. During the experiments, the differences of Pn between CK treatment and 0.2% salt treatment were not obvious. Under 0.3%, 0.4% salt concentration treatments, moreover, net photosynthetic rate gradually decreased with salt concentration increasing. Under salt stress, PAR and Ci can promote photosynthesis of mulberry seedlings.Na ⁺ content of six mulberry varieties is maximum among three measured ion. Na ⁺ mass cumulation in plants can inhibite the absorption of K ⁺, Cl^-,leading to ion toxicity, nutritional imbalance or deficiency.The salty injury of mulberry seedlings may be caused mainly by the single salt ion toxicity. Under salt stress,the content of Na⁺ in the leaves is the most abundant, followed by stems,and roots was the lowest .So ,mulberry leaf is the main site of damage by salt.Through the correlation analysis of each index available, the membrane permeability, MDA, soluble protein, chlorophyll content, net photosynthetic rate, stomatal conductance, root activity can be used as more reliable indicators to evaluate the salt tolerance for six clonal varieties of Morus alba L.,and other indicators as a reference index.The order of salt tolerance capabilities of six clonal varieties of Morus alba L.is: Lucha1>Nongsang12>Anglv1> Husang32>Changsheng>Guisangyou12.