| The density of wheat planting can have a significant impact on the quality of population and individual development,and is a cultivation management measure to effectively control the quality of unit area and population.Too high planting density may cause individual stunting,while too low planting density may result in insufficient total number of stems in the population,thus affecting the occurrence of tillers,tiller characteristics and growth and development of wheat.Planting density can improve photosynthetic radiation and photosynthetic efficiency of leaves,which can further increase the yield of the crop.This experiment was conducted at the Experimental Station of Shandong Agricultural University South Campus in 2018-2020,and the multi-spike variety Shanong 20(SN20)and the large-spike variety Shanong 11(SN11)were selected as the test materials with planting densities of 75(D1),150(D2),225(D3),300(D4),375(D5),and 450(D6)million plants per hectare,respectively.The effects of planting density on the distribution and content of cytokinin,gibberellin and abscisic acid in roots,tiller nodes and leaves during the tillering stage of wheat were analyzed and compared to clarify the roles of different endogenous hormones in tiller development.The effects of planting density on canopy light interception,photochemical efficiency,photosynthetic effective radiation and spike stem development were also investigated to clarify the differences in light energy utilization and dry matter accumulation and distribution among different wheat groups.The above study aimed to elucidate the physiological mechanisms of planting density regulation of wheat tillering and yield formation,and to provide theoretical basis for the construction of high quality wheat populations.The main findings of this experiment are as follows.1.Effect of planting density on the content of endogenous hormones in roots,tiller nodes and leaves and the total number of stems in the population of wheat at the tillering stageAt different planting densities,the total number of stems in the SN20 population during the wheat tillering stage differed significantly between treatments with more than 3 million plants per hectare and less than 2.25 million plants per hectare,which was consistent with the difference between the gibberellin content in the tiller nodes of each treatment.The gibberellin content was highest in the tiller nodes while cytokinin was highest in the leaves.higher gibberellin content in SN11 than SN20 and lower cytokinin than SN20 were the possible reasons for the significant differences in the number of SN20 populations with density.The abscisic acid content in the leaves of multi-spike SN20 and large-spike variety SN11 was always lower than that in the root system and tiller nodes under all treatments during the tillering stage and differed significantly from them.abscisic acid content in the root system of SN20 was the highest under D2 treatment,which was 80.78% higher than that in the leaves.And the abscisic acid content in each part was not significantly correlated with cytokinin,gibberellin and population number in other parts.2.Spike stem development and material accumulation in response to different planting densitiesThe difference in spike stem length between treatments of the multi-spike variety SN20 was more significant than that between treatments of the large-spike variety SN11,where the difference between treatments of different densities of SN20 gradually increased after flowering,indicating that the growth of the spike of the multi-spike variety was more sensitive to the response of cultivation factors such as density,and the low density treatment contributed more to the increase in spike length.At 20 days after flowering,the fresh weight of SN11 spikes was smaller than that of SN20,while the fresh weight of stems was larger than that of SN20,and the differences between the density treatments were significant.At the same time,the spike fresh weight and stem fresh weight of SN11 treatments showed significant differences earlier than that of SN20,which showed that the density difference had a greater effect on the later spike and stem development of SN11 than that of SN20,making a significant difference between the yield of SN11 low density and high density treatments.The single stem dry matter weight of both multi-spike variety SN20 and large-spike variety SN11 reached the maximum at 30 days after flowering for D1 and D3 treatments,respectively,and the D3 treatment of SN11 was 19.46% higher than the D1 treatment of SN20.3.Response of light energy use efficiency of wheat populations to different planting densities after floweringIn the late stage of wheat fertility,the two spike wheat varieties showed the same trend of SPAD change as the fertility period progressed,but SN20 showed significantly higher values in D1,D2 and D3 treatments than in D4,D5 and D6 treatments from 0 to 20 days after flowering,and the SPAD value was the largest under D3 treatment.fluorescence parameters at 20 days after flowering of SN20 differed significantly between treatments,and canopy light interception at 20 days after flowering The canopy light interception showed significant differences between treatments at 20 days after flowering.SN11,on the other hand,showed differences between treatments in all parameters at 30 days after flowering.The maximum photosynthetic quantum yield of PS Ⅱ increased with increasing density in all treatments,with the D6 treatment of SN20 being 2.64%,1.76%,0.97% and 1.57% higher than the D1 treatment at four periods,respectively.As fertility progressed,the maximum photosynthetic quantum yield of photosystem II gradually decreased in SN20,while SN11 showed a trend of first increasing and then decreasing,which indicated that the PS II reaction center of largespike varieties could obtain higher maximum light energy conversion efficiency in late fertility compared with multi-spike varieties.4.Effect of planting density on wheat yieldBoth SN20 and SN11 showed an increasing trend of spike number with increasing density,but on the contrary,the spike number and thousand grain weight showed a decreasing trend,and the overall spike number,spike number and thousand grain weight of SN20 were smaller than those of SN11.The D4 treatment of SN11 had the highest yield,and the difference with D3 and D5 treatments was not significant.Therefore,it can be concluded that the suitable density for high yield is 3.75 million plants per hectare for SN20 and 3 million plants per hectare for SN11.Increasing the planting density of wheat at sowing within a certain range is conducive to achieving higher final yields,with the large-spike variety SN11 having a more prominent group yield advantage at lower planting densities,while the multiple-spike variety SN20 has a more pronounced group yield advantage at relatively higher planting densities. |
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