Light Conversion And Utilization Within Populations And Yield Performance Of Different Leaf Shape Soybeans In Response To Planting Density And Nitrogen Fertilization

Increasing planting density and nitrogen fertilizer application are currently the most effective cultivation measures to improve soybean yields.However,the self-shading of leaves and mutual shading among plants in high planting density population are serious,the light environment in the canopy deteriorates,affect the leaves photosynthetic capacity,and the production capacity of a single plant is reduced.The frequency and amplitude of light fluctuations in the canopy of field crop populations varied greatly,which was very different from that of systematic fluctuations,and at the same time,the two dimensions of light energy-direct light and diffuse light-led to different light utilization capacities of leaves in the canopy,and the amount of photosynthetic carbon assimilation loss in leaves caused by light fluctuations was not clear.The previous studies on fluctuating light were limited to systematic fluctuations,did not differentiate the dimensions of light（direct light and diffuse light）,especially the studies on soybean canopy were even weaker.This experiment was conducted at the Agronomy Experiment Station of Shandong Agricultural University and the Key Laboratory of Crop Water Physiology and Drought-tolerance Germplasm Improvement,Ministry of Agriculture and Rural Affairs during 2020-2023 growing season.The ovoid-leaved soybean cultivar Qihuang 34（QH34,O）and the lance-leaved variety Shanning 24（SN24,L）were selected as the materials,three levels of nitrogen application rate(N0:0 kg hm^–2;N1:120 kg hm^–2;N2:240 kg hm^–2)were set up at three planting densities(D1:90000 plant hm^–2;D2:120000 plant hm^–2;D3:150000 plant hm^–2)set up in each cultivar.Through the study of different nitrogen-density combinations of groups of different canopy dry matter and yield distribution to determine the key branches of single-plant capacity decline,the key branches of the canopy leaves of the photosynthetic potential,the actual photosynthetic performance in the field to analyze,to explore the nitrogen and planting density regulate physiological and biochemical mechanisms of leaves in different leaf shape canopies response to fluctuations and steady of direct and diffuse light.In order to provide theoretical basis and technical support for high-yield and high-efficiency cultivation of soybean and efficient use of resources.The main results were as follows:1 Increased planting density and increased nitrogen application significantly affected light energy distribution within soybeanThe upper canopy of the densely planted and N-application population intercepted a large amount of light,large differences in light distribution among leaf shape varieties,especially of the ovoid leaf shape variety（O-type）intercepted an average of 61.7%of the photosynthetically active radiation（PAR）,which was 19.9%higher than that of the lanceolate leaf shape variety（L-type）.The decrease in PAR from top to bottom within the canopy increased significantly with increasing planting density and N application.The main source of light in the canopy was direct light,dense planting with nitrogen significantly reduced direct light intensity within the canopy and improved light stability.Leaf shape differences are the main cause of light intensity and light fluctuations,the leaves of the high-density and high nitrogen treatment of O-type were in the light environment where the light intensity was weaker and fluctuated less.An advantage in leaf shape exists for L-type,allowing more direct light to be incident into the canopy,higher light intensity but more fluctuation within the canopy.2 Increased planting density and increased nitrogen application significantly increased diffuse light utilizationThe decrease in photosynthetic accumulation induced by increasing planting density was higher within O-type,especially in direct light.The proportion of photosynthesis accumulation under diffuse light increased gradually with increasing density and nitrogen application,and the role of diffuse light with weaker light intensity but less fluctuating was amplified under high planting density,which could compensate for the photosynthetic losses generated by the reduced light intensity and frequent fluctuations of direct light,and contributed to the increase in the proportion of photosynthesis accumulation under diffuse light.3 Increasing planting density and nitrogen application significantly affected fluctuating light use in soybean leavesDirect light fluctuations were the main source of photosynthetic losses,with lower losses of photosynthetic accumulation due to light fluctuations within high planting density,and reduced leaf resistance to fluctuations with increased nitrogen application.O-type had higher relative light use efficiency for diffuse light and L-type had higher relative light use efficiency for direct light.The fluctuations of direct light mainly affected the electron transfer and acceptor-side properties of PSII.In contrast,under diffuse light,the light intensity,which reduced the connectivity or grouping probability of PSII components,the activity of the oxygen-excreting complex,caused the accumulation of Q_A^-,inhibited the transfer of photosynthesis electrons downstream of the electron transport chain,and resulted in a reduction in the amount of photosynthetically accumulated under fluctuating light.4 Increasing planting density and nitrogen application significantly increased the efficiency of nitrogen and light energy use in the lower and upper parts of the canopy of lanceolate varietiesWithin the high-density and nitrogen-applied treatments,there was nitrogen redundancy in the leaves within the lower canopy,while the main problem in the upper canopy layer was the insufficient utilization of light energy,which was particularly serious in the canopy of the O-type.The L-type had significantly higher photosynthetic capacity,light and nitrogen use efficiencies in all canopy layers,and the effect of nitrogen application was more significant for the high-density treatment population of the L-type,which indicated that the L-type was more suitable for high-density planting due to more direct light incident into the canopy and required a moderate amount of nitrogen fertilizer inputs to ensure the high light and nitrogen use efficiencies.5 Increasing planting density and nitrogen application significantly improved dry matter accumulation,nitrogen use efficiency and yield of soybean populationPartial factor productivity of nitrogen,nitrogen utilization efficiency and nitrogen harvest index of soybean increased significantly by increasing planting density.Nitrogen translocation efficiency and nitrogen utilization efficiency of L-type were better than those of O-type.Under the conditions of this experiment,both varieties had the highest dry matter accumulation,nitrogen accumulation and yield in the planting density of 150000 plants hm^–2 and N application rate of 240 kg hm^–2.Increasing planting density and nitrogen application brought about yield increases of 30.0%and 19.7%in O-type and 33.4%and 28.7%in L-type,which showed that the potential for yield increase with planting density and nitrogen application was lower in O-type than in L-type.In conclusion,the two soybean varieties had a clear population advantage at a planting density of 150000 plants hm^–2 and a N application rate of 240 kg hm^–2.The higher stability of diffuse light within the canopy for denser nitrogen application of oval-leaved varieties reduces photosynthetic losses due to fluctuating direct light,and should synergistically improve nitrogen utilization efficiency in the lower layers and light energy utilization efficiency in the upper layers under the existing planting density conditions;the higher direct light within the population of lanceolate varieties with higher photosynthetically effective radiation results in stronger photosynthetic performance of leaves under fluctuating light,and has the potential to increase nitrogen densely to improve yields...