Effect Of Shading On Dry Matter Allocation And Architectural Plasticity Of Different Wheat Genotypes

As wheat chromosome ploidy increasing [diploid(2n)? tetraploid(4n)? hexaploid(6n)] and replacement of new and old cultivars,the different wheat genotypes(Triticum)follows the trajectory of yield improvement at dense planting;however,the underlying ecological mechanisms is not clear.The canopy photosynthetically active radiation(PAR)is reduced due to dense planting,triggering the individual light competition via adjusting dry mass allocation and architectural plasticity.The pot experiments with special shading setup were conducted to simulate the real light condition in dense and sparse planting.In this study,the different wheat genotypes(Experiment 1: diploid,tetraploid and hexaploid wheat genotypes;Experiment 2: new and old hexaploid wheat genotypes)were selected to investigate the effect of shading on dry matter allocation and architectural plasticity in different wheat genotypes.The main findings are as follows:1.As wheat chromosome ploidy increasing,individual plant size and different organs dry weight(DW)increased,as well as grain yield,harvest index and grain yield per ear,while the reduction in leaf fraction,stem fraction and root fraction.The individual plant size was reduced in hexaploid,not in diploid and tetraploid wheat,under shading condition.Shading has no effects on the dry mass allocation in different chromosome ploidy wheat,except for the increasing stem fraction of hexaploid wheat.2.With the increase in wheat chromosome ploidy,plant height,flag leaf area,flag leaf angle and flag leaf projected length increased.The variation in architectural plasticity occurred under shading,thus,improved plant height in all different ploidy wheat and an increase in flag leaf projected length and specific leaf area of tetraploid wheat.It can be seen that under shading conditions,different ploidy wheat can optimize longitudinal light resource competition through high growth;tetraploid wheat also increases lateral light resource competition and shade tolerance.3.In contrast to old cultivars(landrace),the individual plant size and dry weight of organs of new cultivars were decreased,while the grain yield per ear was increased.There is no significant difference in dry matter allocation between the new and old cultivars.In most cases,shading reduced the dry weight of organs of new and old wheat cultivars,while having no effect on leaf dry weight and stem dry weight of old cultivars.Shading has no effect of dry mass allocation for new cultivars,but increasing in leaf fraction and stem fraction in old cultivars and decreasing in harvest index and spike fraction.Therefore,the constant of harvest index in responding to shading allows the new cultivars allocate enough dry biomass to grain at dense planting.4.With the replacement of new and old cultivars,an increase in flag leaf area and decrease in plant height and individual spike numbers were observed.The variation in architectural plasticity occurred under shading.The increase in flag leaf projected length in old cultivars,which is beneficial to the horizontal light capturing.The limited architectural plasticity was found in new cultivars.Therefore,the increased individual plant size and reduced competitive organ fraction(i.e.root,stem and leaf)have occurred during the wheat chromosome ploidy increased;the convergence of architectural plasticity under shading condition and smaller individual plant size were found in the replacement of new and old cultivars.In summary,increased grain yield per ear during wheat evolution,contribute to wheat yield improvement.Meanwhile,reducing competitive organ fraction and convergence of individual architectural plasticity,are beneficial for yield improvement at dense planting.