The Relationship Between Cultivar-Plant Competition And Optimal Population Yield On Northern Winter Wheat Regions

The studying of relationships among population yield,individual competition ability and competitive strategies are becoming hot areas in scientific research.In present study,the field experiments of large scale plot(2.4×5m)with winter wheat(Triticum aestivum L.)were carried out in Shunyi at Beijing,Pingliang in Gansu,as well as Luoyang in Henan on the northern winter wheat region during two wheat growing season from 2016 to 2018.The newly-breeding and high yield cultivar,Zhongmai 175,together with Jingdong 8(Shunyi),Xiping 1(Gansu)and Luohan 2(Luoyang),were selected in three locations.The relationship between cultivar-plant competition and optimal population yield was studied.The field experiment set two densities:the local conventional sowing density and 1.2 times the local conventional density.The competition by de Wit replacement series experiments with ratio of 3:0,2:1,1:2 and 0:3 for control cultivar to Zhongmai 175 were conducted.There were three different neighbor effects that is four same(4/4),half same(2/4)and four different(4/4)neighbor individuals in nearest neighbor positions with central position were formed in uniform planting patterns.The main results are as follows:(1)In local plant density,the grain yield of Zhongmai 175 with 3515,6083,6010 and 5775 kg ha-1 were higher that in the control cultivars with 3155,4270,5049 and 4,756 kg ha-1 in Shunyi(2016-2017/Jingdong 8),Pingliang(2016-2017,2017-2018/Xiping 1)and Luoyang(2016-2017/Luohan 2),respectively.With the increasing of plant density(120%local density),the grain yield of Zhongmai 175 with 4022,6421,5241 and 4942 kg ha-1,were higher that in the control cultivars with 2928,4479,4983 and 4654 kg ha-1 in four environments,respectively.Comparing to the yield in controls,there are yield increasement in Zhongmai 175 were 11.4%,42,5%,19.0%and 21.4%in local plant density,and 37.4%,43.4%,5.2%and 6.2%higher in 120%in local plant density in four environments,respectively.Therefore,there were obvious population yield improvement of Zhongmai 175 on northern winter wheat regions.(2)The relative grain yield(the ratio of grain yield in mixculture to that in monoculture)was used to estimate the competition ability of wheat cultivars.In both plant densities,the competition ability was lower in Zhongmai 175 than control cultivars,Jingdong 8 and Xiping 1,in Shunyi(2016-2017)and Pingliang(2016-2017,2017-2018),respectively.However,the competition ability was higher in Zhongmai 175 than Luohan 2 in Luoyang(2016-2017).Therefore,the optimal population yield was formed in Zhongmai 175 via increasing competition ability in Luoyang(2016-2017),while by decreasing competition ability in the other three environments.(3)With the transition of the four nearest neighbor plants from the same(4/4),half the same(2/4)to different(0/4),the inverse changes in population yield were found in control cultivars and Zhongmai 175 in all environments except Luoyang(2016-2017);the population yield were decreasing in Zhongmai 175,whereas increasing in control cultivars(Jingdong 8 and Xiping 1).The similar trends as mentioned above was found in both densities Shunyi(2016-2017)and Pingliang(2016-2017).However,the grain yield was increasing in Zhongmai 175 and decreasing in control in Luohan as control cultivar in Luoyang(2016-2017)with the increase of the number of different neighbor plants.(4)The plant competition ability is regulated by vertical and horizontal“shade avoidance"strategies and "shade tolerance" strategies under light competition.In four environments,the height was lower in Zhongmai 175 than control cultivars.With the transition of the four nearest neighbor plants from the same(4/4),half the same(2/4)to different(0/4),the plant height of Zhongmai 175 increased,while which decreased or unchanged in control cultivars.These results showed that Zhongmai 175 adopted vertical "shade avoidance",to allocate more in plant height responding to taller neighbor plants of control cultivars.In most environments,the individual spike numbers were higher in Zhongmai 175 than control cultivars.Here,the individual spike number was estimated the horizontal "shade avoidance" strategy,which represent horizontal light capture.The result in Luoyang(2016-2017)showed that Zhongmai 175 adopted horizontal "shade avoidance" to increase individual spike number in responding to taller neighbor plants of control cultivars,while individual spike number of Luohan 2 was decreasing while more neighbors of Zhongmai 175 surrounded.The individual spike number of Zhongmai 175 were decreasing in responding to taller neighbor plants of control cultivars in Shunyi and Pingliang,which indicated the Zhongmai 175 did not adopted horizontal "shade avoidance" strategy in these environments.However,the opposite trends of individual spike number in control cultivars were also found in these environments.Under competitive conditions,increasing specific leaf area is the plasticity response of plants to strengthen“shade tolerance" strategy.With the transition of the four nearest neighbor plants from the same(4/4),half the same(2/4)to different(0/4),the specific leaf area of Zhongmai 175 increased,while which decreased or unchanged in control cultivars.In Luoyang(2016-2017),Zhongmai 175 and Luohan 2 showed opposite trend.Under the condition of light competition,the differentiation of vertical and horizontal "shade avoidance" strategies and "shade tolerance" strategies between Zhongmai 175 and control varieties showed a similar trend at the two density levels.In summary,the studying of complex relationships among crop population yield,individual competition ability and light competition strategies of winter wheat cultivars contrasting yield formation indicated that crop population yield improvement follow the trajectory of reducing individual competitive ability in Shunyi(2016-2017)and Pingliang(2016-2017,2017-2018).This can explain the grain yield improvement of Zhongmai 175 in most environments.However,the increasing of individual competition ability was beneficial to population yield formation in Zhongmai 175 in Luoyang,because of wheat adaptation enhancement.Therefore,the risk of "tragedy of commons"(TOC)would be occurred due to higher inter-plant competition,such as Jingdong 8 and Xiping 1.Suppression population yield formation was also occurred because of weaken inter-plant competition due to less adaptation,for example Luohan 2.Under light competition,the optimal population yield in Zhongmai 175 were obtained in Shunyi and Pingliang,by avoiding occurrence of TOC with weaken competition ability via decreasing plant height and specific leaf area;while in Luoyang through increasing plant height and individual spike number to enhance its adaptation.