Studyon Photosynthetic Physiological Functionof Graftingto Improve Salt Toleranceof Mulberry

By choosing the southern high-quality and high-yield varieties as scions,the grafted mulberry can not only solve the overwintering problem of high-quality and high-yield mulberry varieties spread in the north,but also improve the yield and the quality of the leaves of the northern mulberry.What is more encouraging is that in our study,we also found that the salt tolerance of grafted mulberry has been improved to a certain extent.In order to find out the physiological basis of increasing salt tolerance of mulberry(Morus alba L.)by grafting,self-rooted seedlings Tiepa'(high yield of leaves and good quality)was used as the control in this experiment,the experiment group was the grafting seedlings obtained from the local mulberry variety 'Qinglong'(strong salt tolerance)as rootstock and'Tiepa' as scion.The effects of 0,50,100,150 and 200 mmol·L-1 salt stress on the absorption and transport of Na+and K+in root system were studied,the responses of leaf nitrogen and phosphorus content,PS II photochemical activity and metabolism of reactive oxygen species(ROS)to salt stress were also discussed.The results are as follows:1.Salt stress changed the content of Na+and K+in root and leaf of mulberry.Na+content in root and leaf of self-rooted seedlings and grafted seedlings increased with the increase of salt concentration under salt stress,the content of Na+in roots and leaves of grafted mulberry trees was lower than that of self-rooted seedlings when the salt concentration was lower than 100 mmol·L-1,and the content of Na+in roots and leaves of grafted mulberry trees was lower than that of self-rooted seedlings.Under salt concentration above 100 mmol· L-1,the content of Na+in root and leaf increased obviously,and the grafted was lower than that of self-rooted mulberry.There was no significant difference in root and leaf K+content between self-rooted and grafted seedlings when salt concentration was below 150 mmol·L-1,When the salt concentration reached 200 mmol·L-1,the content of K+in root and leaf of grafted mulberry seedlings was 50.8%and 55.9%higher than that of self-rooted seedlings.2.Under the different salt concentration,the grafted seedlings of mulberry showed relatively high root activity,which played an active role in the absorption of water and nutrients in mulberry.Low concentration of salt stress did not change the leaf and root nitrogen and phosphorus content,but higher concentration of salt stress decreased the leaf and root nitrogen and phosphorus content.With the increasing of salt concentration,the content of nitrogen and phosphorus in the leaves of self-rooted and grafted mulberry seedlings decreased,when the salt concentration was lower than 150 mmol·L-1,there was no significant difference in leaf N content between self-rooted and grafted seedlings of mulberry compared with CK.When the salt concentration increased to 200 mmol·L-1,the leaf nitrogen content of grafted mulberry seedlings was 38.3%higher than that of self-rooted seedlings.When the salt concentration was 150 and 200 mmol·L-1,the phosphorus content in the leaves of grafted seedlings was 16.32%and 38.44%higher than that of self-rooted seedlings,respectively.Under different concentration of salt stress,the fresh weight and dry weight of grafted mulberry seedlings were significantly higher than those of self-rooted seedlings under the influence of nutrient and moisture.3.When the salt concentration reached 50 mmol·L-1,the photo synthetic performance index(PIABS)based on light absorption energy of grafted mulberry leaves was significantly higher than that of root seedlings.O2·-production rate in the leaves of grafted seedlings was significantly higher than that of self-rooted seedlings.When the salt concentration reached 100 mmol·L-1.the ratio of energy absorbed by the leaves of grafted seedlings to the electron transfer after QA-(?Eo)was significantly higher than that of self-rooted seedlings.The maximum quantum yield of non-photochemical quenching(?Do)of grafted seedlings was significantly lower than that of self-rooted seedlings.The change trend of ETo/RC ratio and DIo/RC ratio for thermal dissipation is consistent withc?Eo and?o.The ratio of light absorption energy per unit reaction center to photochemical reaction is different from that of?Eo/?Do.The content of H2O2 in the leaves of grafted seedlings was significantly higher than that of self-rooted seedlings.When the salt concentration reached 200 mmol L-1,the PS ? maximum photochemical efficiency(Fv/Fm)of grafted seedlings was significantly higher than that of self-rooted seedlings.The increase of light energy(ABS/RC)absorbed by the unit response center of the grafted seedlings was significantly lower than that of the self-rooted seedlings.In conclusion,grafting with salt-tolerant rootstocks can reduce Na+uptake and transport to leaves by root system of mulberry seedlings under salt stress.Moreover,the leaves of grafted mulberry seedlings had relatively high root activity under salt stress,promoted the absorption of N,P.K and other nutrients by grafted mulberry seedlings under salt stress,and increased plant biomass accumulation.PS II photochemical activities of grafted mulberry seedlings under salt stress were higher than those of self-rooted seedlings.Especially under salt stress,the inhibition of PS II electron acceptor side electron transport capacity of grafted mulberry seedlings was alleviated,so the production of reactive oxygen species was effectively decreased.Therefore,using "Qinglong" with strong salt tolerance as the rootstock,and grafting"Tiepa" with high yield and good quality shows strong salt-tolerant ability.