Effects Of Winter And Spring Night Warming On Grain Yield Formation In Wheat And Its Physiological Mechanism

Warming is the main impact of global climate change.Global warming shows diurnal warming asymmetry.The increments of temperature amplitude in winter and spring are greater than in summer and autumn,and warming is greater at night than during the day.The quality,yield and physiological characteristics of wheat will be significantly affected by warming because wheat is the type of warm and cool.The senescence rate of flag leaf of wheat which was closely related to the photosynthate supply and finally effect the formation of grain yield.Understanding the impact of winter and spring night warming on winter wheat grain yield and flag leaf senescence has important significance.In this study,two winter wheat cultivars,Yangmai 13(spring wheat variety)and Yannong 19(semi-winter wheat variety),were tested.Field experiments were conducted to investigate the effects of night warming during winter and spring seasons on grain yield formation of wheat.The physiological mechanism of the effect of increasing temperature in winter and spring on the yield formation was explained by photosynthesis,sugar and nitrogen metabolism,antioxidant capacity and membrane lipid peroxidation.Besides,another experiment was conducted to study the effects of night warming during winter and spring seasons on flag leaf senescence characteristic and grain yield under night warming during grain filling stage of wheat.The purpose of this study was to provide a theoretical basis for wheat production potential and high yield cultivation in the context of climate warming.The main results are as follows:1.The grain yield of wheat was increased by pre-anthesis growth rate and dry mass production capacity under the winter and spring night warming.Winter night warming significantly enhanced grain yield by increasing grain number and 1000-grains weight for both cultivars,while the spring night warming treatment was only slightly different from the control.The grain dry matter accumulation during grain filling stage was increased under winter and spring night warming.Meanwhile,winter and spring night warming increased the grain filling rate at early and middle growth stage of wheat,which resulted in increasing the grain weight.Both warming treatments shortened pre-anthesis growth duration and lengthened post-anthesis growth duration,which resulted in higher post-anthesis growth degree days(GDD).Winter night warming treatment increased the crop growth rate(CGR)and biomass at anthesis and maturity,which also resulted in increasing pre-anthesis translocation amount(PTA),post-anthesis accumulation amount(PAA)and contribution of post-anthesis accumulation to grains(CPA),but the increments were much higher for winter night warming treatment than for the spring night warming treatment.Furthermore,winter night warming increased the leaf area index(LAI),leaves area per stem and leaf area ratio at anthesis,thus coordinated the source-sink relationship of wheat.Winter and spring night warming improved the production capacity of winter wheat by promoting the pre-anthesis growth rate and the development of source sink organ,which were conducive to the improvement of grain yield.The yield characteristic of the two wheat cultivars was consistent under the warming treatment.Increasing the N application increased the positive effect on yield of winter and spring night warming.2.The winter and spring night warming increased the flag leaf photosynthetic capacity at the early stage of grain filing,besides,the balance of source-sink sugar and nitrogen metabolism was coordinated,which was conducive to grain yield increase.Winter and spring night warming enhanced the net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),maximum efficiency of PSII photochemistry under dark-adapted(Fv/Fm)and actual photosynthetic efficiency(?PS?)of flag leaves at the early stage of grain filling for both cultivars,while the increases were higher for winter night warming treatment than for the spring night warming treatment.It showed that night warming not only increased the photosynthetic rate,but also improved the photosynthesis ability.In addition,soluble protein content and Rubisco content had different degrees of improvement during the early stage of grain filling,while the increase was higher in winter night warming treatment.Meanwhile,winter and spring night warming up-regulated the Rubisco activase B encoding gene RcaB and the major chlorophyll a/b-binding protein gene Cab at anthesis.However,the flag leaf senescence rate were higher during late stage of grain filling under winter and spring night warming treatment,thus reduced the winter wheat photosynthetic capacity.Winter night warming increased the nitrogen assimilation and utilization ability by increasing the flag leaf nitrogen content and NR,GS ability.Winter and spring night warming increased the flag leaf soluble sugar and sucrose content in the early stage of grain filling.Meanwhile,SPS activity of flag leaf increased,thus improved the ability of photosynthetic product transformed into sugar,in order to lay the foundation of increasing grain sucrose content and SS activity,while the increase was higher in winter night warming treatment than in spring night warming treatment.At the same time,winter and spring night warming coordinated the balance of grain endogenous hormones,which was beneficial to grain dry matter accumulation.Consequently,the winter wheat flag leaf showed high photosynthetic capacity at early stage of grain filling under the winter and spring night warming acclimation,which could maintain the stability of photosynthetic system and produce more photosynthetic products.Besides,the increase of grain SS activity and the balance of endogenous hormones enhanced the ability of sink,which was conducive to grain yield increase.3.Under the winter and spring night warming treatment,the flag leaf senescence was delayed by improving the antioxidant capacity and reducing the membrane lipid peroxidation at the early stage of grain filling,which was the important reason for the high yield.Winter and spring night warming decreased the O2·-production rate and MDA content of flag leaves after anthesis of winter wheat,which indicate that the senescence rate of flag leaf at the early stage of grain filling was delayed,while the senescence rate was sped up at the late stage of grain filling.Meanwhile,the SOD activity,POD activity and CAT activity of flag leaves at early stage of grain filling were increased under winter and spring night warming treatment,while decreased at late stage of grain filling.This indicate that the flag leaf antioxidant capacity at the early stage of grain filling was improved under winter and spring night warming treatment,the trend was consistent with the expression of Cu/ZnSOD,MnSOD and CAT.Moreover,winter and spring night warming decreased the content of PLD,PA,LOX and FFA in the flag leaves.As a result,the membrane lipid peroxidation level of flag leaf at the early stage of grain filling was decreased,while the decrease was higher in spring night warming treatment than in winter night warming treatment.The membrane lipid peroxidation level was increased at the late stage of grain filling.Besides,the IAA and CTK content were increased while the ABA content was decreased at the early stage of grain filling,which was beneficial to coordinate the balance of endogenous hormones in the flag leaf.Winter and spring night warming could delayed the flag leaf senescence rate at the early stage of grain filling,which was beneficial to photosynthesis.4.Winter and spring night warming relieved the grain yield decrease under night warming during grain filling stage by delayed the flag leaf senescence after anthesis.The night warming during grain filling stage decreased the grain yield by decreasing grain number and 1000-grains weight,while the decreases were lower after winter and spring night warming.Meanwhile,winter and spring night warming enhanced the net photosynthetic rate(Pn),chlorophyll content,chlorophyll fluorescence parameters,soluble protein content and Rubisco content of flag leaf,thus increased the photosynthetic capacity under night warming during grain filling stage,while the trend was consistent with the expression of RcaB and Cab.In addition,winter and spring night warming treatment inhibited the membrane lipid peroxidation level by enhancing the activity of SOD and POD of flag leaves at the early stage of grain filling,thus inhibited the flag leaf oxidation degree expression of Cu/ZnSOD and MnSOD.The membrane lipid peroxidation level was decreased at the early stage of grain filling under the pre-anthesis night warming.Winter and spring night warming relieved the grain yield decrease under night warming during grain filling stage by delayed the flag leaf senescence after anthesis.In conclusion,winter and spring night warming improved the production capacity of winter wheat by promoting the pre-anthesis growth rate and the development of source sink organ.Besides,it induced expressions of related genes,improved capacities of flag leaf photosynthesis and anti-oxidation,coordinated the balance of sugar nitrogen metabolism and grain endogenous hormones,thus increased the grain yield of winter wheat.Besides,winter and spring night warming relieved the grain yield decrease under night warming during grain filling stage by delayed the flag leaf senescence after anthesis.Increasing the N application increased the positive effect on yield of winter and spring night warming.