Fffects Of Nitrogen On Drought Tolerance In Different Genotypes Of Wheat At Seedling Stage Under Drought Stress

Water shortage and soil barren are two important environmental factors restriciting plant growth and development factors in Northwest China.Water and nutrients not only have their own special effects,but also affect the yield and quality of crops.In this paper,two kinds of wheat with different panicle types?Xinong 979and Large-spike 2036?were used as the research materials.We studied the root activity,leaf photosynthesis and chlorophyll fluorescence of wheat,active oxygen metabolism and metabolism regulation of antioxidants,respectively by artificial control method.The response,regulation and adaptation of two wheat varieties to different water and nutrients were studied to investage the difference between the two wheats.This study has great significance in revealing the drought tolerance mechanism of wheat seedlings and the regulation mechanism of nitrogen on drought.It provides theoretical basis and technical support for wheat to use its nutritional genetic characteristics to mine its absorption and to utilize the physiological potential of nitrogen.The main results are as follows:?1?The purposes of this study were to investigate the effects of water and N coupling on root vigor and uptake of nitrogen in Wheat.Two different cultivars of wheat Xinong 979 and Large-spike 2036 was planted in Hoagland nutrient solutions.Three treatments of different N levels,i.e.low N?0.5 mM NO₃^-?,normal N?8 mM NO₃^-?and high N?16 m M NO₃^-?and three water regimes,i.e.well-watered?no stress?,moderate drying?8%PEG?and severe drying?15%PEG?were conducted.The results showed that there was a significant interaction between water regimes and N supply.Severe water stress could decrease the biomass,total absorbing surface,activity absorbing surface,root vigor,nitrogen content and nitrogen accumulation in wheat.Nitrogen deficiency increased the root length and root/shoot,decreased the biomass,total absorbing surface,activity absorbing surface,activity/total absorbing surface,root vigor,nitrogen content and nitrogen accumulation significantly.The root total absorbing surface,activity absorbing surface and root vigor of Xinong 979increased significantly,and it was also 11%,14%,27%higher than Large-spike2036respectively at a high N level compared with low N and normal N levels.Root N accumulation and shoot N accumulation in Xinong 979 had no significant difference between normal N and high N levels.And the plant N accumulation of Xinong 979was 13%⁶2%higher than Large-spike 2036 at normal N level.The root–shoot ratio?R/S?increased slightly with water stress at a low N level;the smallest root–shoot ratio was found at a high N level and moderate drought stress treatment.Correlation analysis showed that activity absorbing surface,root vigor was positively correlated to plant N accumulation?P<0.01?,while there was extremely significant negative correlation between activity absorbing surface,root vigor and root/shoot?P<0.01?.A negative correlation was observed between root/shoot and plant N accumulation?P<0.01?.The increase of nitrogen supply can improve the absorbing surface and root vigor of Xinong 979 effectively,but excessive nitrogen supply was not conductive to the root growth of large-spike wheat.These results suggested that the root vigor and growth of wheat with different genotypes respond differently to water and nitrogen coupling.Optimal regulations of water and N supply are beneficial to the formation of good root morphology and increased root vigor,therefore leading to the enhanced ability of absorbing moisture and nutrients.?2?In our study,two winter wheat varieties,Xinong 979 and Large-spike wheat,were evaluated for their physiological responses to different levels of nitrogen and water status during their seedling stage grown in a phytotron.Our results indicated that drought stress greatly reduced the net photosynthetic rate?Pn?,transpiration rate?Tr?,and stomatal conductance?Gs?,but with a greater increase in instantaneous water use efficiency?WUE?.At the meantime,the nitrogen?N?supply improved photosynthetic efficiency under water deficit.Parameters inferred from chlorophyll ameasurements,i.e.,photochemical quenching coefficient?qP?,the maximum photochemical efficiency?Fv/Fm?,the quantum yield of photosystem?(?_PS?),and the apparent photosynthetic electron transport rate?ETR?decreased under water stress at all nitrogen levels and declined in N-deficient plants.These results suggest that an appropriate nitrogen supply may be necessary to enhance drought resistance in wheat by improving photosynthetic efficiency and relieving photoinhibition under drought stress.However,an excessive N supply had no effect on drought resistance,which even showed an adverse effect on plant growth.Comparing the two cultivars,Xinong979 has a stronger drought resistance compared with Large-spike 2036 under N deficiency.?3?The ROS accumulated in the wheat under ow nitrogen concentration.MDA decreased with the increase of nitrogen content.The concentrations of ROS andMDA in the root of large-spike wheat were higer than those of Xinong 979 under drought stress.Underthe drought stress,the concentrations of ROS,POD,ASA,and GSH increased with nitrogen addition.Especially,the protective enzyme activity increased under mild drought stress.The POD and CAT activity and the GSH concentration of Xinong 979 were higher than those of Large-spike wheat under low nitrogen.It indicates that the oxidation resistance and active oxygen control ability of Xinong 979 is stronger than Large-spike wheat under drought stress,nitrogen addition can increase the antioxidant enzyme activity under the absent of drought stress,and only the suitable nitrogen addition could increase the enzyme activity of leaves under water stress.Moderate nitrogen addition could increase the drought resistance of wheat and mitigate the damage of ROS to wheat cells.