Effect Of Salt Stress On Characteristics Of Photosyhthetic And Physiology Of Rice Varieties Under Different Nitrogen Levels

Two north japonica rice varieties (Jiudao13and Jijing88) were used as materials tounderstand the role of different concentrations of nitrogen in improving salt tolerance of rice.Jiudao13was salt tolerant rice variety and Jijing88was salt sensitive rive variety. Two ricevarieties were cultured in phytotron with hydroponics and rice plants which were cultured atdifferent nitrogen levels were stressed at early booting stage. The variation of plant height,biomass, photosynthetic characteristics and some physiological characteristics were measured atbooting stage after salt stress of different salt concentration. This research aimed to providingthe theoretical basis for breeding of salt-tolerant rice varieties and high yield cultivationtechniques under salt stress.The results showed that:1Effect of salt stress on plant height and biomass under different nitrogen levelsPlant height of two varieties were decreased under salt stress, plant height of1N levelsdidn’t reach significant differences to control, and there were significant differences betweenother nitrogen levels and control. Fresh weight and dry weight of above grounds and roots ofplants were decreased significantly under salt stress, harm of leaves was greater than that ofstems under salt stress. Fresh weight and dry weight of above grounds and roots showed a singlepeak curve which increased at the beginning and then decreased with the increase of nitrogenlevels. Biomass of roots at low nitrogen levels was higher than that of high nitrogen levels.Compared with the control, decline of biomass at1N level was the least at each saltconcentration.2Effect of salt stress on photosynthestic characteristics of rice leaves under different nitrogenlevelsThe net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) andapparent mesophyll conductance (AMC) of two rice varieties were decreased significantly undersalt stress. Pn, Gs, Trand AMC of rice leaves showed a single peak curve which increased at thebeginning and then decreased with the increase of nitrogen levels. Intercellular CO2concentration (Ci) and stomatal limitation (Ls) of rice leaves cultured in low nitrogen levelschanged little, which indicated that the reduction in Pn was due to non-stomatal restrictionfactors in low-nitrogen-levels. While in high nitrogen levels, Ciwere decreased significantly,and Lswere increased significantly after salt stress, it indicated that the stomatal limitationfactors and non-stomatal limitation factors resulted in the reduction in Pn in high-nitrogen-levels. Ciwere decreased more obviously, and Lswere increased more significantly with the increase ofsalt concentration, which indicated a gradual increase of stomatal limitation. Meanwhile AMCof two rice varieties were decreased significantly, it indicated that the decline of RuBPCaseactivity was a mean non-stomatal limiting factors which leaded to decline of rice netPhotosynthetic rate. Pn, Gs, Trand AMC of Jiudao13were higher than that of Jijing88atdifferent treatment, and after salt stress, decline of Pn, Gs, Trand AMC of Jiudao13was less thanthat of Jijing88, which indicated that photosynthetic capacity of Jiudao13was higher than that ofJijing88under salt stress.3Effect of salt stress on physiological characteristics of rice leaves and roots under differentnitrogen levels.Activity of antioxidant enzymes such as SOD, POD, CAT of two rice varieties wereincreased significantly, and content of soluble sugars and proline accumulation in leaves androots were increased significantly under salt stress. Content of MDA and membranepermeability were increased significantly of two varieties under salt stress. Activity ofantioxidant enzyme and content of soluble sugar and proline of salt tolerant variety were higherthan that of salt sensitive variety. Meanwhile content of MDA and membrane permeability ofsalt tolerant variety were lower than that of salt-sensitive variety. Under salt stress, activity ofantioxidant enzymes such as SOD, POD, CAT, content of proline and soluble sugar of leaves in1/2N-level nutrient solution were significantly higher than that at other nitrogen-levels,membrane permeability and content of MDA at1/2/N-level were lower than that at othernitrogen-levels. We suggested that rice varieties cultured in1/2N-level nutrient solution couldimprove the capacity of osmotic regulation, and enhance salt-tolerance ability of rice varieties atbooting stage.4Effect of salt stress on Characteristics of Chlorophyll Fluorescence in Rice leaves undernormal nitrogen levelContent of chlorophyll, maximal fluorescence (Fm), Fv/Fo, Fv/Fm, Fv’/Fm’, ΦPSII, acyclicquantum transfer efficiency (ETR) and photochemical quenching (qP) of rice varieties weredecreased under salt stress, and initial fluorescence (Fo), non-photochemical quenching (qN)were increased. Each index which were increased or decreased of salt-sensitive variety werehigher than of salt tolerant variety. It indicated that tolerant varieties could keep thephotochemical activity of PS Ⅱe ffectively under salt stress, and dissipated the excess energy byheat more effectively to protecting the photosynthetic structure to avoid excessive decline ofphotosynthetic rate.This research showed that biomass of plants, photosynthetic rate of rice varieties were decreased under salt stress, content of proline and soluble sugar, activity of antioxidant enzyme,content MDA and membrane permeability of rice varieties were increased under salt stress.Each indicators of salt-tolerant rice variety were better than that of salt-sensitive variety.Biomass accumulation and photosynthetic capacity of rice plants cultured at nutrient solution of1/2nitrogen levels maintained a high level, and content of proline and soluble sugar, activity ofantioxidant enzyme of rice plants cultured at nutrient solution of1/2nitrogen levels were thehighest of all treatment. Increase of content of MDA and membrane of rice plants cultured atnutrient solution of1/2nitrogen levels were the in minimum comparing with control. Wesuggested that rice varieties cultured in1/2N-level nutrient solution could improve the capacityof osmotic regulation, and enhance salt-tolerance ability of rice varieties at booting stage.