Regulatory Effects And Physiological Mechanism Of Sowing Pattern And Planting Density On Yield And Nitrogen Use Efficiency In Winter Wheat

Wide sowing strip planting（WSP）and increased planting density have the effect of improving wheat yield and nitrogen use efficiency.However,but the physiological mechanisms of wide sowing strip planting to improve yield and nitrogen use efficiency as well as the regulatory effects and physiological mechanisms of the interactions between wide sowing and planting density on yield and nitrogen use efficiency are not clear.Exploring the potential of yield and nitrogen use efficiency improvement and its physiological mechanism of reasonable matching between wide sowing and dense planting can provide theoretical basis and technical support for further improving the yield and nitrogen use efficiency of dense planted wheat populations.In this study,Taimai 198 strong tillering capability was selected as experimental plants during the 2017-2021 wheat seasons.Two planting patterns,wide sowing strip planting（seedling width 8cm and row spacing 27 cm）and conventional sowing pattern（seedling width3 cm and row spacing 27 cm）were selected.The effects of different sowing on canopy structure,photosynthetically active radiation interception rate,photosynthetic capacity,photosynthetic product distribution,root size from different soil depths,nitrogen uptake efficiency,total nitrogen uptake,and nitrogen utilization efficiency of winter wheat were thoroughly investigated.In the 2020 to 2022 wheat season,two winter wheat cultivars with lower and higher tillering capability（Shannong30 and Taimai198,respectively）and three plant densities of lower,medium,and higher(Taimai 198 with 150 m^–2,210 m^–2 and 270 m^–2;Shannong 30 with225 m^–2,300 m^–2 and 375 m^–2)were selected to investigate the effects of planting density,planting pattern,and their combination on the nitrogen uptake and utilization,canopy green area index,the photosynthetically active radiation interception rate,specific green area nitrogen content,radiation use efficiency（RUE）,biomass accumulation,the harvest index,and grain yield.The main results are as follows:1 Physiological mechanism of yield increase in wide sowing strip plantingCompared with conventional sowing pattern,the distance of wide sowing strip planting between plants within rows was increased,while the distance between plants in different rows was decreased,which significantly affected the canopy structure of wheat at anthesis and after anthesis.Compared with conventional sowing pattern,under wide sowing strip planting,specifically,the leaf length of the flag leaf shorter,the leaf width remained unchanged,the leaf area decreased by 11.51%on average,the leaf inclination angle decreased significantly,and there were no significant changes in leaf length,leaf width,leaf area and leaf inclination angle of the other leaf;there was a slight increase in the spacing from spike to flag leaf auricle and flag leaf auricle to leaf 2;and there were no significant in the plant height.Due to the increase in the number of spikes per unit area,the leaf area index of the flag leaf layer remained unchanged,while the leaf area index of the other leaf layers increased significantly.Compared with conventional sowing pattern,under wide sowing strip planting,the leaf 2layer photosynthetic active radiation and interception rate of wheat at anthesis and after anthesis were significantly increased 13.09%and 34.12%.At the same time,the nitrogen content per unit area of the leaf 2 layer average significantly increased by 12.57%at after anthesis.The net photosynthetic rate per unit leaf area of the leaf 2 layer averaged significantly increased by12.13%,which significantly increased photosynthetic potential（24.99%）and the transport of¹³C–labeled assimilates from the leaf 2 layer to the grain(39.82 mg m^–2).The net photosynthetic rate,leaf area index,photosynthetic potential,and translocation of ¹³C–labeled assimilates to grains in the flag leaf layer remained unchanged.In the other leaf layers,the net photosynthetic rate remained unchanged or decreased slightly,the leaf area index increased significantly,photosynthetic potential and the translocation of ¹³C–labeled assimilates to the grains also increased significantly.As a result,the dry matter accumulation at maturity increased,the harvest index remained unchanged,and the yield increased.2 Physiological mechanisms of improving nitrogen use efficiency by wide sowing strip plantingCompared with conventional sowing pattern,under wide sowing strip planting,the number of tillers,spikes and dry matter accumulation per plant and per unit area in each key period of wheat increased significantly,which in turn increased the nitrogen demand and nitrogen storage capacity of aboveground plants.The number of roots per plant and per unit area,root dry weight,root/shoot ratio,root length density and root surface area density increased significantly in the whole soil profile during booting stage,but the specific root length and surface area of the total dry weight remained unchanged,and the total nitrogen uptake in the 0–120 cm soil layer increased significantly,and the nitrogen uptake efficiency and nitrogen use efficiency increased significantly.Observation by soil layer found that compared with conventional sowing pattern,the root length density and root surface area density in the 0–40cm soil layer under wide sowing strip planting increased by 28.30%and 22.55%respectively,although the ¹⁵N–uptake efficiency of root length and root surface area increased by 12.34%and 8.32%.Since the effect of the former is much greater than the latter,the absorption of ¹⁵N in the 0–40 cm soil layer was increased by20.03%.Compared with conventional sowing pattern,the root length density and root surface area density in the 40–80 cm soil layer increased by 22.34%and 29.32%respectively,and the root length density and root surface area density in the 80–120 cm soil layer increased by 13.67%and 20.58%respectively,and ¹⁵N–uptake efficiency of root length of the 40–80 cm and 80–120cm soil layers increased by 6.35%and 7.29%respectively.Although there is no significant difference in the ¹⁵N–uptake efficiency of root surface area of the 40–80 cm and 80–120 cm soil layers.The ¹⁵N–uptake of in the 40–80 cm and 80–120 cm soil layers increased by 30.10%and 21.95%,respectively.The increase in uptake of ¹⁵N in the 40–80cm soil layer was greater than that in the 0–40 cm and 80–120 cm soil layers.3 Effects of combining wide sowing strip planting with dense planting improve yield and nitrogen use efficiencyThe average of the two planting pattern,when the planting density increased from low density to high density,the pre–anthesis dry matter transfer to the grain of Taimai 198 and Shannong 30 increased by 10.79%,8.86%,and the post–anthesis dry matter production increased by 16.11%,13.99%,respectively;changing the conventional sowing pattern to wide sowing strip planting,the two cultivars of the pre–anthesis dry matter transfer to the grain increased by 7.89%,respectively,5.63%,post–anthesis dry matter production increased by11.28%,8.85%;wide sowing strip planting with dense planting a reasonable combination of two cultivars of pre–anthesis dry matter to grain transfer increased by 19.20%,14.93%,post–anthesis dry matter production increased by 28.87%,23.95%.Dense planting significantly reduces the harvest index,sowing pattern change has no significant effect on the harvest index,wide sowing strip planting with dense planting reasonable combination,harvest index slightly reduced.The average of the two planting patterns,when the planting density increased from low density to high density,the yield of Taimai 198 and Shannong 30 increased by 15.43%and13.13%respectively;changing the conventional sowing pattern to wide sowing strip planting,the yield of the two cultivars increased by 10.85%and 8.31%respectively,and wide sowing strip planting with dense planting a reasonable combination of two cultivars increased by27.62%,respectively,22.41%.Under conventional sowing pattern,with the increase of planting density from low density to high density,the grain yield of Taimai 198 and Shannong 30increased by 12.82%and 12.04%,respectively;under wide sowing strip planting,with the increase of planting density from low density to high density,the grain yield of Taimai 198 and Shannong 30 increased by 17.84%and 14.13%,respectively.It is obvious that the yield increasing effect of increasing planting density under wide sowing strip planting conditions is significantly higher than that of conventional sowing pattern,the yield increasing effect of increasing planting density is greater than that of changing the sowing pattern,and the yield increasing effect of the reasonable combination of wide sowing strip planting with dense planting increasing is greater than that of the independent effect of increasing density and changing the sowing method.The magnitude of change in nitrogen use efficiency is consistent with yield.4 Physiological mechanism of increasing yield and nitrogen use efficiency by combining wide sowing strip planting with dense plantingPlanting density increased from low density to high density,the canopy green area index of Taimai 198 and Shannong 30 increased by 23.21%and 16.87%respectively,and the photosynthetically active radiation interception rate increased by 14.43%and 13.86%respectively;changing the conventional sowing pattern to wide sowing strip planting,the canopy green area index of the two cultivars increased by 7.95%and 6.65%respectively,and the photosynthetically active radiation interception rate increased by 2.47%and 2.22%respectively.Wide sowing strip planting with dense planting,two cultivars of wheat canopy green area index increased by 28.41%and 25.04%,respectively,photosynthetically active radiation interception rate increased by 18.01%,16.54%,respectively.Planting density increased from low to high density,the specific green area nitrogen content of Taimai 198 and Shannong 30 decreased by 9.94%and 13.24%,Rubisco activity decreased by 10.48%and9.40%,and RUE decreased by 5.46%and 4.00%,respectively;changing the conventional sowing pattern to wide sowing strip planting,specific green area nitrogen content of two cultivars increased by 2.12%,2.22%,Rubisco activity increased by 3.80%,3.36%,RUE increased by 6.61%,5.87%;wide sowing strip planting with dense planting,the two cultivars of specific green area nitrogen content were reduced by 7.21%,8.17%,Rubisco activity was reduced by 8.29%and 3.37%,and the RUE remained unchanged.Planting density increased from low density to high density,the aboveground nitrogen accumulation and nitrogen uptake efficiency of Taimai 198 and Shannong 30 increased by26.99%and 22.06%respectively,the nitrogen harvest index decreased by 14.86%and 11.73%,the nitrogen content of the grain decreased by 6.29%and 7.73%,and the nitrogen utilization efficiency was reduced by 9.15%and 7.32%respectively.Changing the conventional sowing pattern to wide sowing strip planting,cultivars of aboveground nitrogen accumulation and nitrogen uptake efficiency increased by 11.92%,8.62%,nitrogen harvest index increased by2.63%,2.53%,grain nitrogen content increased by 3.85%,2.89%,nitrogen utilization efficiency did not change significantly.Under conventional sowing pattern,the planting density increased from low density to high density,and for every 1%increase in the absolute value of nitrogen uptake efficiency of Taimai 198 and Shannong 30,the nitrogen utilization efficiency decreased by 0.19 kg kg^–1,0.15 kg kg^–1,and the corresponding values under wide sowing strip planting conditions were 0.12 kg kg^–1,0.11 kg kg^–1.Wide sowing strip planting with dense planting,aboveground nitrogen accumulation and nitrogen uptake efficiency of the two cultivars were increased by 41.87%,32.47%,nitrogen harvest index was reduced by 12.47%,9.35%,nitrogen content of grains was reduced by 2.67%,1.93%,and the nitrogen utilization efficiency was reduced by 10.05%and 7.58%,respectively.Dense planting strengthened the photosynthetically active radiation interception and wide sowing strip planting improved the RUE,which significantly increased the canopy apparent photosynthesis in densely planted wheat fields.Wide sowing strip planting with dense planting further increased aboveground nitrogen accumulation and nitrogen uptake efficiency,while mitigating the reduction of nitrogen utilization efficiency,and both synergistically further improved wheat nitrogen use efficiency.In summary,under wide sowing strip planting,the canopy structure of wheat population was optimized,the leaf area index was increased,the production of post–anthesis photosynthesis products and the translocation to the grain were significantly increased,in which the flag leaf layer remained unchanged,the inverted leaf 2,leaf 3,leaf 4 layers were significantly increased,the dry matter accumulation of the population was increased,and the harvesting index was unchanged,so as to achieve the increase in yield.Wide sowing strip planting significantly increased root length density and root surface area density in each soil layer,which reduced the nitrogen uptake efficiency of root length density in the surface soil layer,but increased the nitrogen uptake efficiency of root length density in the middle and lower soil layers,thus,the total nitrogen uptake in the 0–120 cm soil layer increased significantly,and the nitrogen uptake efficiency and nitrogen use efficiency increased significantly.Wide sowing strip planting with dense planting,under the premise of increasing photosynthetically active radiation interception,the radiation use efficiency under high–density population was maintained by improving specific green area nitrogen content,which in turn increased the canopy photosynthetic rate;meanwhile,the simultaneous increase in wheat yield and nitrogen utilization was achieved by alleviating the contradiction between the increase in nitrogen uptake efficiency and the decrease in nitrogen utilization efficiency.