Regulation And Physiological Basis Of The Spike Formation Of Winter Wheat Tillers By Supplemental Irrigation With Different Depth Of Wetting Layers At The Jointing Stage

Jointing stage is the key period for the formation of productive tillers and water demand of winter wheat,but it is easy to suffer the winter and spring drought in this stage which leads to the decrease of the spike number,grain yield and water use efficiency.In order to provide a theoretical basis for the research and development of rational irrigation technology,a 2-year field experiment?from 2017 to 2018 and from 2018 to 2019?was performed in Xuanzhuang Village?36°12?N,116°54?E?,Daiyue District,Tai'an City,Shandong Province,to study the effect of soil moisture at jointing on the spike formation of the main stem and tillers of winter wheat.Shannong 23?SN23?and Shannong 29?SN29?were selected as experimental materials and three wetting layers were used for irrigation at the jointing stage:0–10 cm?T2?,0–20 cm?T3?,and 0–30 cm?T4?.A treatment with no irrigation at jointing?T1?served as the control.The amount of supplemental irrigation?SI?was calculated by I=10·?·H·??_i-?_j?,where the target relative water content??_i?was the 100%field capacity.All the treatments were performed under movable shelter conditions,and the canopy was covered when rain fell during the period from wintering to anthesis.The amount of SI from sowing to wintering and from anthesis to maturity was determined by a method of threshold judgment?DB 37/T3174–2018?for winter wheat.1 Effect of supplemental irrigation on the soil water content.After irrigation at the jointing stage,T3 and T4 showed that the soil relative water content in the 0–100 cm soil layers was reached to 72.0–75.8%and 72.7–76.3%,respectively,compared with that in T1.However,there was no significant difference in the relative water content in the 100–200 cm soil layers among T2,T3 and T4 treatment.There was no significant difference in the relative water content in the 0–200 cm soil layers between T3 and T4 treatment at anthesis,which was significantly higher than that in T1 and T2.These results indicated that the soil relative water content in the 0–100 cm soil layers at jointing and0–200 cm soil layers at anthesis increased significantly with the increasing depth of wetting layer for irrigation at the jointing stage.2 Effect of supplemental irrigation on grain yield and water use efficiency?WUE?of winter wheatThere was no significant difference in grain yield between T3 and T4 treatment in both cultivars,which was significantly higher than that in T2.Compared with T3 treatment,T4 had no significant difference in grain yield,however,the WUE decreased significantly.This result indicated that the higher grain yield and the highest WUE were obtained with the depth of wetting layer was 0–20 cm in both the large-and multi-spike cultivar.The increased amplitude of grain yield and WUE in SN23 were significantly higher than those in SN29.This result indicated that the optimal soil moisture at jointing significantly increased the grain yield and WUE in the large-spike cultivar than that in the multi-spike cultivar.3 Effect of supplemental irrigation on the population dynamic and the rate of spike formation of winter wheatWithin a given cultivar,the reduction amplitude of tiller numbers per unit area from jointing to anthesis was showed with T4<T3<T2<T1.There was no significant difference in the spike numbers between T3 and T4,which was significant higher than that of T2.These results indicated that irrigated with the moderate wetting layer depth at jointing significantly delayed the rate of tillers mortality and promote the formation of spike.For the tiller ? in SN23 and tiller ? in SN29,there was no significant difference in the rate of spike formation between T3 and T4,which was significantly higher than T2.The rate of spike formation of the tiller ? in SN23 and tiller ? in SN29 were increased with the increasing depth of wetting layer used for irrigation at jointing.There was no significant difference among T2,T3 and T4in the rate of spike formation of tiller ? in SN29.These results indicated that the rate of spike formation of the tillers with higher position in the lager-spike cultivar was more sensitive to drought at the jointing stage than that in the multi-spike cultivar.The rate of spike formation of tillers in both cultivars significantly increased when the depth of wetting layer was increased from 0–10 cm to 0–20 cm,particularly tiller ? and ? in the multi-spike cultivar.4 Gas exchange characteristics of different tillers from jointing to anthesisThe photosynthetic rate?Pn?,transpiration rate?Tr?and instantaneous water use efficiency(WUE_leaf)of the apical leaf were significantly decreased with the increasing of tiller position from jointing to anthesis.For the Pn of apical leaf of the main stem and tiller ? in both cultivars,there was no significant difference between T3 and T4 treatment,which was significantly higher than that in T2,and T1 was the lowest.The Pn of apical leaf of the tiller ? was highest in T4 treatment.The Tr of apical leaf of different tiller was showed with T4>T3>T2>T1,while the WUE_leafeaf was showed with T1>T2>T3>T4.These results indicated that the Pn of the main stem and tillers with lower position was significantly increased with the depth of wetting layer for irrigation at jointing was 0–20 cm,while there was no significant difference in the Pn of the apical leaf between the main stem and the tillers with lower position and significantly increased the Pn of the tillers with higher position when the depth of wetting layer increased to 0–30 cm.The Tr of different tillers increased significantly,led to an increased invalid water consumption and a decreased WUE_leaf.5 Senescence characteristic of different tillers from jointing to anthesisFor the main stem and tiller ? in SN23,the SOD and CAT activity,soluble protein content were increased with the increasing depth wetting layer used for irrigation at jointing,which was showed with T4>T3>T2>T1.For the main stem and tiller ? in SN29,there was no significant difference in SOD and CAT activity,soluble protein content between T3 and T4treatment,which was significantly higher that in T2.The antioxidant enzyme activity of tiller ? in both cultivar significantly increased with the increasing depth wetting layer used for irrigation at jointing.The MDA content in different tillers were significantly decreased.These results indicated that the antioxidant enzyme activity of different tillers was significantly increased when the depth of wetting layer for irrigation at jointing increased from 0–10 to0–20 cm,however,the antioxidant enzyme activity of different tillers in the large-spike cultivar increased significantly when the wetting layer reached to 0–30 cm,while there was no significant effect on the multi-spike cultivar.6 Carbon and nitrogen accumulation of different tiller from jointing to anthesisThere was no significant difference in the rate of soluble sugar accumulation and the rate of nitrogen accumulation of the main stem and tiller ? in SN23 and SN29,but the rate of dry matter accumulation of tiller ? in SN23 and SN29 was significantly higher than that in the main stem.However,the accumulation amount of soluble sugar,nitrogen and dry matter at anthesis was decreased 43.22–49.56%,36.40–53.97%and 39.71–52.54%in SN23,respectively,and 28.83–32.03%,20.19–25.81%and 22.46–29.93%in SN29,respectively.The soluble sugar,nitrogen and dry matter accumulation of tiller ? showed no obvious change regularity from jointing to anthesis.For the main stem and tiller ? in both cultivars,the rate of soluble sugar accumulation was showed with T4>T3>T2>T1;there was no significant difference in the rate of nitrogen and dry matter accumulation between T3 and T4 treatment,which was significantly higher than that in T2.For the tiller ?,there was no significant difference in the rate of soluble sugar,nitrogen and dry matter accumulation among T2,T3and T4 treatment,but higher than that in T1.These results indicated that the rate of carbon and nitrogen accumulation of the main stem and tillers with lower position was significantly increased when the depth of wetting layer increased from 0–10 to 0–20 cm,while there was no significant difference in the rate of carbon and nitrogen accumulation between the main stem and the tillers with lower position and had no significant effect on the tiller ?.However,the difference in the carbon and nitrogen accumulation amount between the tillers and the main stem of the large-spike cultivar at anthesis were significantly higher than that of the multi-spike cultivar.In summary,the proportion and number of tillers altered into productive tillers in the large-spike cultivar?SN23?were more sensitive to the soil moisture condition at the jointing stage than those in the multi-spike cultivar?SN29?.Moderate irrigation at jointing significantly increased the SOD and CAT activity and soluble protein content of the main stem and tillers with lower position,delayed the senescence of tillers and increased the Pn of apical leaf of tillers,which was significantly promoted the accumulation of nitrogen and dry matter of the main stem and tillers with lower position,improved the rate of spike formation of tiller ? and III in both cultivars,and increased the spike number and grain yield.However,excessive irrigation at the jointing stage significantly increased the Tr of apical leaf of different tillers and decreased the WUE_leaf,led to the reduction of WUE.Regardless of the large-and multi-spike cultivar,irrigation at the jointing stage brought the soil water content in the 0–20 cm profile to 100%of field capacity significantly increased the rate of spike formation of the main stem and tillers,which resulted in both high grain yield and WUE.