| The repressive mechanism of salt stress on plant growth is very complicated. The salt tolerance among plant with different varieties are variable. Sweet potato is one of main food crops, forage and potential energy crops, and is sensitive to chlorine in former reports. Chlorine is one of essential micro-nutrient elements for crops, excessive accumulating of chloride would lead to pernicious effect on the plant. The understanding among different genotypes of sweet potato seedlings, response to slat and chloride stress is important in agriculture application and plant application in filed. Researches were conducted with hydropnic culture in incubator in the laborary of agricultural resources and environment institute of Jiangsu Academy of Agricultural Sciences during2010to2012, based on the screen of reliable Cl-determination methods, the influence of NaCl or different concentration exogenous chlorine treatment to sweet potato seedling growth, photosynthetic characteristics, ion distribution in the plant and the dynamic change of nutrient absorption preliminary were studied to reveal the response of mechanism of NaCl, chlorine stress. The results showed that:Using the recovery (standard addition) method analyzed chloride contents of sweet potato seedlings of six different cultivars. Results showed that the silver nitrate titration method was low in reproducibility and it was also hard to determine when to end the titration; the ultraviolet spectrophotometry was low in chloride recovery, ranging from52.9%to81.4%, and analysis of samples was influenced by the color of sample extraction solvent; whilst the automatic potentiometric titration method was high in chloride recovery rate, reaching high in the range from93.9%to105.5%with relative standard deviation being0.6%～6.0%, and moreover, the method was simple to use, good in reproducibility and high in accuracy. Therefore, the automatic potentiometric titration method is the best one in determination of chloride in sweet potato.Salt stress showed significant inhibition on seedlings growth and "Xushu18""Xushu22","Zhezil","Fushu062-20" appeared higher salt tolerance than other varieties. Ions of Na+and Cl-increased markedly and salt-ion content accumulation in shoots was much more than those in roots NaCl stress led to decrease of K+and Ca2+contents. The K+/Na+ratio of "Fushu062-20"’,"Zhezil","Xushu18" were slightly higher than "Baiweishao","Yanshu25","Xucail" under salt stress. The Ca2+/Na+ratio there are little difference exists in various sweet potato varieties, but "Fushu062-20"."Zhezil""Xushul8" higher in Sca,Na.Relative water content (RWC) values in the leaves of different sweet potato cultivars were above75%under salt treatment and no significant differences were found among different cultivars. The chlorophyll content index(CCI), net photosynthetic rate (Pn), stomatal conductance (Gs) and instantaneous water-use efficiency(iWUE) decreased with increasing salt concentration."Zhezil" and "Xushul8" had the highest values of CCI and Pn. However, Gs of "Zhezil" was greatly influenced by salt concentration with the salinity susceptibility index (SSI)22%. The reason for the reduction in photosynthetic rate of "Xushu18","Chuan211" and "Zhezil" was stomatal limitations.The biomass, growth rate of vine length, leaf area and NPK accumulation of sweet potato seedlings were influenced by exogenous chlorine stress."Xushu22" was depressed by using exogenous chlorine, but was able to maintain a certain level. On the contrary."Sushu11" and "Ningzil" were able to maintain an increase in the same condition using the extra Cl-(concentration of84.4mmol·L-1). Non-stomatal limitation is the main cause for the decreasing of photosynthesis of "Xushu22"."Sushull" and "Ningzil" show both non-stomatal limitation and stomatal limitation, which stomatal limitation is the more dominating when samples are under temporary or low concentrated exposure of Cl-.Exogenous chlorine at the concentration from42.2to168.8mmol·L-1promotes the production of CCI, and the production capacity of "Xushu22" is more than "Sushu11" which is higher than "Ningzil". The concentration of MDA increases slightly under the treatment with exogenous chlorine. The concentration of Cl-in the roots of sweet potatoes of21d is more than that of14d while their SCl are higher, demonstrating that seedlings can effectively restrain the translocation of Cl-to the aerial part, which is weakened after3weeks of treatment with exogenous chlorine. In addition, NR activity and NO3- concentration increase under the treatment with low concentration of exogenous chlorine(Cl-≤84.4mmol·L-1) for21d. thereby promote the concentration of total nitrogen. |
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