Effects Of Drought Priming And Nitrogen Application On Physiological Characteristics And Water Use Efficiency Of Wheat

Water and nitrogen are the main limiting factors for agricultural productivity in arid and semi-arid regions.There have been many studies on the effects of drought stress and nitrogen on crop physiology and water use efficiency and the effects of drought priming on crop drought resistance.However,the effect of nitrogen application on drought priming and the effects of water and nitrogen on water use efficiency of crops under drought priming conditions are still unknown.Therefore,in this study,the effects of nitrogen application,nitrogen application level and after drought priming on wheat growth,the relationship between physiological processes and hormone transduction and leafδ¹³C,as well as the effects of nitrogen and drought priming on wheat water use efficiency were studied.Using the greenhouse pot culture method,experiment 1 was designed:no nitrogen（N0）and nitrogen fertilization（N1,1.5 g N every pot）,and three water treatment under each nitrogen level consisting of full irrigation（CK）,rewatering（PW）and redrought stress（PD）after drought priming（Soil Water Content（SWC）was60%of Soil Water Holding Capacity（SWHC））.Based on experiment 1,designed experiment 2:three nitrogen levels of low nitrogen（N0.5,0.5 g N every pot）,medium nitrogen（N1.5,1.5 g N every pot）and high nitrogen（N3,3 g N every pot）,and three water treatments at each level:rewatering to 85%of SWHC（W85）,rewatering to 60%of SWHC（W60）and redrought stress to 40%of SWHC（W40）after drought priming（SWC was 40%of SWHC）.The main research conclusions are as follows:（1）When the soil water content of the drought priming was 60%,either rewatering or redrought stress reduced the water status of plant roots.Root water potential（RWP）was significantly positively correlated with soil water content（SWC）,so RWP was directly affected by SWC changes,and thus determined the water status of the aboveground part of plants.N1PD treatment significantly reduced RWP,significantly increased abscisic acid（ABA）concentration of leaves,strengthened hydraulic and chemical signals,so that the reduction of stomatal conductance（g_s）was greater than the effect on leaf net photosynthetic rate（P_n）,and the internal water use efficiency of leaves(WUE_int)was significantly improved.（2）Nitrogen application,rewatering and redrought stress after drought priming all promoted the accumulation of root dry biomass（RDB）,which was conducive to the uptake of limited water and nutrients by roots.PW and PD treatments increased plant water use efficiency（WUE_P）by reducing plant water use（PWU）while ensuring shoot dry biomass（SDB）accumulation.Nitrogen application promoted plant growth,increased SDB higher than PWU,and increased WUE_p.WUE_p and leafδ¹³C of N1PD treatment was the highest,followed by N1PW treatment.（3）When the soil water content of drought priming was 40%,rewatering improved the water status of plants,but the degree of rewatering should not be too high when nitrogen is supplied normally or a small amount of nitrogen is supplied.The water status of the shoot was directly affected by SWC changes,and the ABA concentration of leaves was directly affected by water status and decreased significantly with the increase of rewatering degree.Compared with leaf water status,g_s had a higher correlation with leaf ABA concentration,which was mainly regulated by chemical signals.High nitrogen supply or reduced rewatering degree significantly reduced leaf g_s and increased WUE_int by enhancing plant hydraulic and chemical signals.（4）Proper nitrogen application or reducing the rewatering degree after drought priming increased the RDB,contributing to the root growth.Both increasing nitrogen application and rewatering after drought priming significantly increased leaf area（LA）,but excessive nitrogen supply and rewatering cannot increase LA in proportion.There was a significant positive correlation between WUE_p and leafδ¹³C,which could be used to characterize the level of WUE_p under drought stress.Among all treatments,N3W85 and N3W60 had a higher WUE_p while ensuring SDB accumulation,but N3W60 significantly reduced PWU while not significantly affecting SDB accumulation.Moreover,N3W60 had a higher root-shoot ratio,which was more conducive to the growth of wheat plants and save irrigation water,and was the optimal treatment in this study.Therefore,in arid and water-scarce areas,increasing nitrogen application and moderate rewatering after drought priming,which can not only significantly reduce PWU,save irrigation water,maintain crop growth and nutrient absorption,but also increase WUE_int and WUE_p.