Effects Of Low Temperature In Spring On Wheat Yield And Defensive Remedy Of Fertilize Nitrogen

The global climate changes lead to frequent nature disasters,which have a great impact on crop production.Low-temperature disasters in winter and spring have disadvantageous effects on wheat growth and development and formation of yield.With spring wheat cultivar Yangmai 16,semi winter variety Xumai 30,Canadian spring wheat AC Carberry,AAC Scotia and Hoffman as the experimental varieties,low temperature stress was imposed at the appearance of the penultimate leaf,booting stage and anthesis to investigate the effects of low temperature stress on formation of yield and physiological mechanisms underlying spike infertility.The objectives of this study are to develop a strategy to mitigate the negative effects of low temperature stress around jointing stage by applying 15N fertilizer,analyze the mechanism of increasing the resistance of stem to low temperature stress by spraying plant growth regulators(PGRs),and develop measures to compensate for the loss from low temperature stress.This study is of critical importance for providing theoretical basis and technical support relieving cold stress to stablize wheat yield.The main results were as follows:1.The grain yields of Yangmai 16 and Xumai 30 were reduced significantly when low temperature was imposed at the appearance of the penultimate leaf(5/-3℃)and at booting stage(8/-1℃)and anthesis(12/4℃).The reductions in kernel number per spike and spike numbers were the main reason for production decline at the appearance of the penultimate leaf,while the reductions in the kernel number per spike and thousand-kernel-weight were the main reason for declined productivity at booting stage and anthesis.Therefore,stabilizing spike number and increasing spike weight is the main way to stable yield under low temperature stress.The length of internode and the height of wheat plant were decreased by low temperature stress at the three stages.The low temperature stress at the appearance of the penultimate leaf significantly reduced the length of the second basal internode,the length of spike height of wheat plant.The low temperature stress at booting stage significantly affected plant height,the length of internode below spike and spike length.2.Low temperature in spring significantly reduced the photosynthetic rate of wheat leaves.The SPAD readings of Yangmai 16 and Xumai 30 at the appearance of the penultimate leaf and at the stages of booting and anthesis declined until the third day after the treatment of low temperature,then rose gradually to normal level at the 6th day after the treatment of low temperature.The photosynthetic rate,stomata conductance and transpiration rate of the leaves of the two varieties were significantly decreased with the proceeding of low temperature treatment.However,the concentration of intercellular CO2 and chlorophyll fluorescence value(Fv/Fm)were significantly increased during the low temperature stress.3.There were stress effects imposed by low temperature observed at the appearance of the penultimate leaf and at the stages of booting and anthesis,with recordable increase in the activities of SOD,POD,CAT and the content of proline.The low temperature at the appearance of penultimate leaf had the greatest effect on the activity of antioxidant enzymes.Low temperature seriously damaged cytomembrane and the content of MDA was remarkably increased as compared with the control.The content of MDA reflects the destruction of,which increased significantly after cold stress.4.The low temperature at booting stage affected the meiosis of pollen mother cell,which affected the formation of gametophyte.Besides,low temperature at the stages of appearance of penultimate leaf,booting,and anthesis reduced the activity of pollen grain.The pollens of spherical abortion type,iodine abortion type,and stained abortion type were observed.The highest percentage of infertile pollen was recorded at booting stage.Low temperature imposed at the appearance of the penultimate leaf and at booting stage reduced spikelet number and kernel number per spikelet,increased the number of degenerated spikelet.The weight of both superior grains and inferior grains was reduced by low temperature at three stages,and the bigger reduction was recorded for the inferior grains.5.Fertilizing nitrogen before cold stress strengthened the cold resistance capacity of main stem,reduced the inhibition on internode elongation,decrease the loss of main stem grain yield.Fertilizing nitrogen after cold stress compensated the loss of grain yield of effective tillers.The application of precautious measures increased the proportion of N of main stem grain from jointing fertilization to total nitrogen accumulated amount,while the application of remedial measures increased the proportion of N of effective tillering grain from jointing fertilization to the total nitrogen accumulated amount.6.The spray of plant growth regulator(PGR)Palisade relieved the damage caused by low temperature,increased the proportion of sclerenchyma and parenchyma,cross sectional area and breaking-resistant strength of the second basal intemode,and the germination percentage of pollen,chlorophyll fluorescence value(Fv/Fm),kernels per spike and TKW were also increased.Spraying PGR could remit the effect of low temperature on yield.