| Warming is a main impact of global climate change.Global warming causes diurnal warming asymmetry,as the amplitude of the temperature increases in winter and spring are greater than those in summer and autumn,and warming is greater at night than during the day.As an important ecological factor,temperature increase is bound to have a significant impact on soil N supply and wheat N uptake and utilization.It is an urgent problem to clarify the relationship between wheat soil N supply and wheat N uptake and utilization under warming conditions and their responses to warming.Field experiments combined with soil column experiments were conducted using Yangmail3 and Yannong19 winter wheat cultivars to investigate the effects of night warming(winter,spring and winter+spring average night temperature increased 1.50?,1.73? and 1.57?)on wheat N utilization,soil N supply and balance,root N uptake,and fates of N fertilizer in soil-wheat system,and based on the previous results,to investigate the effects of basal top-dressing ratio and seeding rate on wheat N utilization under night warming and its mechanism,in addition,to explore the effects of night warming priming on wheat N utilization under grain filling night warming.These results are intend to provide a theoretical basis for improving wheat N use efficiency and reducing soil N loss in the warmer future.The main results are as follows:1.Night warming enhanced soil N supply to improve pre-anthesis N accumulation,and promoted N distribution in leaves at anthesis and post-anthesis N translocation,resulted in increased wheat N utilization efficiency with reduced soil N loss.Night warming increased the N utilization efficiency of both cultivars,and winter+spring night warming has more advantages than winter night warming and spring night warming.Night warming increased pre-anthesis N accumulation rate to increase plant N accumulation,resulted in improved the N recovery efficiency(NRE).Moreover,night warming promoted N distribution and N distribution percentage in leaves at anthesis to increase the N concentration,and increased the net photosynthetic rate,maximum photochemical efficiency,actual photochemical efficiency and soluble protein content of flag leaves in 0-14 days after anthesis,resulted in improved the N agronomic efficiency(NAE).Furthermore,night warming increased pre-anthesis N translocation and post-anthesis accumulation,resulted in improved the N harvest index(NHI).The activities of nitrate reductase and glutamine synthase in leaves were increased in response to night warming,resulted in enhanced the N assimilation and translocation ability,which was conducive to N accumulation and translocation.Soil urease and protease activity as well as the net N mineralization rate were increased in response to night warming,resulted in improved soil N supply capacity,while soil inorganic N amount and soil apparent N surplus were obviously decreased,which was caused by highly improved plant N accumulation,resulted in reduced soil N loss.2.Night warming improved upper root growth and distribution,resulted in increased recovery of 15N fertilizer and reduced loss of 15N fertilizer.Night warming increased the recovery of 15N fertilizer while reduced the residual and loss of 15N fertilizer,and the recovery increases of top-dressed 15N fertilizer were higher than those of basal 15N fertilizer,indicating that night warming increased recovery of 15N fertilizer mainly by increasing recovery of top-dressed 15N fertilizer.Moreover,night warming increased pre-anthesis root growth rate in 0-60 cm soil layer,and the increases were greater in 0-20 cm soil layer than in 20-60 cm soil layer,resulted in improved root biomass and morphology,which favored increasing recovery of 15N fertilizer.Furthermore,residual 15N fertilizer content in 0-100 cm soil layer was reduced,which was associated with improved root weight density in 0-60 cm soil layer,resulted in reduced leaching losses of 15N fertilizer.The path analysis showed that root dry matter distribution in 0-20 cm soil layer was the most important in contribution to increasing recovery of 15N fertilizer and reducing losses of 15N fertilizer compared with other soil layers.3.Under night warming condition,increasing the top-dressing ratio and seeding rate were conducive to improve wheat N utilization efficiency and reduce soil N loss.Under night warming condition,compared with N5/5(basal fertilizer:jointing fertilizer:booting fertilizer 5:3:2),N3/7(basal fertilizer:jointing fertilizer:booting fertilizer 3:5:2)increased the N utilization efficiency of both cultivars.N3/7 increased N accumulation rate from jointing to anthesis,which was conducive to improve NRE.Moreover,N3/7 increased leaf N content of single stem,which was conducive to improve NAE.In addition.N3/7 reduced the soil N surplus from sowing to jointing,and alleviated the soil N deficit from anthesis to maturity,resulted in reduced the total soil N surplus.Under night warming condition,compared with D225(225×104 plants ha-1),D300(300×104 plants ha-1)increased the N utilization efficiency of both cultivars.D300 increased pre-anthesis N accumulation rate,which was conducive to improve NRE.Moreover,D300 increased spikes and maintained higher leaf N content of single stem,which was conducive to improve NAE.In addition,D300 reduced soil N surplus from jointing to anthesis,resulted in reduced the total soil N surplus.4.Under night warming condition,increasing the top-dressing ratio and seeding rate were conducive to increase recovery of 15N fertilizer and reduce loss of 15N fertilizer.Under night warming condition,compared with N5/5,N3/7 increased the recovery and residual of 15N fertilizer and reduced the loss of 15N fertilizer.N3/7 had no effect on root growth rate from sowing to jointing,while mainly increased root growth rate in 0-20 cm soil layer from jointing to anthesis,resulted in improved root biomass and morphology,which favored increasing recovery of 15N fertilizer.Moreover,N3/7 reduced the loss of 15N fertilizer from sowing to jointing to reduce the loss of 15N fertilizer.In addition,N3/7 improved root weight density,which was conducive to reduce leaching losses of 15N fertilizer.Under night warming condition,compared with D225,D300 increased the recovery of 15N fertilizer,and reduced the residual and loss of 15N fertilizer.D300 mainly increased pre-anthesis root growth rate in 0-20 cm soil layer,resulted in improved root biomass and morphology,which favored increasing recovery of 15N fertilizer.Moreover,D300 reduced the loss of 15N fertilizer from jointing to anthesis to reduce the loss of 15N fertilizer.In addition,D300 improved root weight density,which was conducive to reduce leaching losses of 15N fertilizer.5.Night warming priming could delay flag leaf senescence and maintain a better photosynthetic and N assimilation capacity after anthesis,thus alleviating the decreases of N utilization efficiency caused by grain filling night warming.Grain filling night warming significantly reduced the N utilization efficiency of both cultivars,while the decreases were lower in night warming priming.Night warming priming improved the net photosynthetic rate,maximum photochemical efficiency and actual photochemical efficiency of flag leaves after anthesis,which was conducive to the photo synthetic accumulation after anthesis,resulted in alleviated the decreases of NAE.Moreover,night warming priming increased the activity of nitrate reductase and glutamine synthase and soluble protein content in the flag leaves after anthesis,which was conducive to N assimilation and accumulation after anthesis,and the post anthesis N accumulation and its contribution rate to grain were increased,resulted in alleviated the decreases of NRE.In addition,night warming priming increased SOD and POD activity,and decreased O2-production rate and MDA content of flag leaves,resulted in delayed the leaf senescence,which was conducive to maintain the photosynthetic and N assimilation capacity of winter wheat.In conclusion,night warming enhanced soil N supply capacity,promoted pre-anthesis upper root growth and increased leaf N assimilation ability to increase wheat plant N accumulation,meanwhile promoted N distribution in leaves at anthesis and enhanced post-anthesis photosynthesis and N translocation ability of flag leaves to increase N accumulation and yield of grain,eventually resulted in improved wheat N utilization efficiency,and reduced soil N loss.Moreover,under night warming condition,increasing the basal top-dressing ratio and seeding rate improved pre-anthesis upper root growth to increase the N utilization efficiency of winter wheat.Furthermore,night warming priming could delay flag leaf senescence to maintain a better photosynthetic and N assimilation capacity after anthesis,thus alleviating the decreases of N utilization efficiency caused by grain filling night warming. |
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