| Increasing plant density was a key measure to increase maize yield.However,with the increase of plant density and the frequent occurrence of extreme climate,maize faced serious lodging problem,which restricted the increase of maize yield and mechanized harvesting.Spraying chemical regulators could effectively enhance the lodging resistance of maize,thus reduce lodging rate and yield loss.However,when the plants did not lodge,spraying chemical regulators often led to a reduction in maize yield.Therefore,the anti-lodging variety Zhengdan 958 was selected for a two-factor split-plot experiment in this study,with planting density(PD)as the main treatment factor:4.5(D1),6.0(D2),7.5(D3)and 9.0(D4)ten thousand plants per hectare,and the sub-plot was treated with the chemical regulator"Jindele"(EC)at seven-leaf stage:water control(CK),2 mL L-1 EC(T1)and 4 mL L-1 EC(T2).The physiological mechanism of the chemical regulator that influenced the yield and lodging resistance of maize under different densities was explored.The main research results were shown below:1.The main reason for the yield reduction after EC treatments was the decrease in kernel number per ear,and increasing planting density was an effective measure to increase maize yield.After EC treatments,compared with CK,yield and kernel number per ear under low planting densities(D1,D2,and D3)were decreased by 4.8%-9.0%and 3.3%-12.2%,respectively,while there was no significant difference among various EC treatments under high planting density(D4).Accordingly,EC treatments had no significant effect on thousand kernel weight at all plant densities.With the increase in plant density,leaf area index significantly increased,and yield showed a significant increasing trend.2.EC treatments improved the plant structure and canopy photosynthetic characteristics of maize,and alleviated yield losses caused by insufficient source supply to a certain extent.After EC treatments,leaf area index was significantly decreased by 8.9%-32.2%;plant height,ear height,center of gravity height,and the 2nd to 4th based internodes length were significantly decreased,while the plant horizontal-vertical ratio was significantly increased by 4.8%-22.9%.The light transmittance and net photosynthetic rate of the ear position were significantly increased by 4.1%-72.7%and 19.6%-22.9%,respectively.3.EC treatments reduced the concentration of non-structural carbohydrates(NSCs)in maize stems and led to a decrease in kernel number per ear.After EC treatments,the concentration of stem NSCs(starch and soluble sugars)were significantly decreased by 1.6%-17.1%,and the concentration of sucrose and starch in grains were decreased by an average of 13.7%and 12.9%,respectively.Enzyme activities related to grain sugar metabolism(cell wall invertase,sucrose synthase,and ADP-glucose pyrophosphorylase)and polyamines concentration in grains were also decreased slightly.The concentration of NSCs in the stem and grain,grain enzyme activities and polyamines concentration were significantly positively correlated with kernel number per ear.4.EC treatments enhanced the lodging resistance of maize,and the increased stem structural carbohydrates(SCs)were competed with NSCs,exacerbating yield loss.EC treatments were significantly increased the stem diameter at the first based internode,the total number and area of vascular bundles at the third based internode,and the puncture strength between the 3rd and 5th based internodes.After EC treatment,the stem breaking resistance was significantly increased by 12.1%-168.8%compared with the control.In addition,the application of EC could increase the concentration of stem SCs(cellulose,hemicellulose,and lignin),and the SCs concentration were significantly negatively correlated with kernel number per meter and yield.5.EC treatments reduced nitrogen uptake efficiency,but increased nitrogen utilization efficiency(NUtE)and harvest index(HI)of maize.After EC treatments,total nitrogen uptake was significantly decreased by 7.4%-69.0%,while NUtE and HI were significantly increased by 4.3%-31.3%and 1.1%-5.8%,respectively.Dry matter of each organ was decreased after EC treatments,but the transfer amounts of dry matter and nitrogen and the contributions to grains were increased.The plant horizontal-vertical ratio was significantly positively correlated with NUtE and HI,promoting nutrient transportation.However,the decrease in dry matter and total nitrogen uptake of maize after EC treatments limited the formation of yield.In conclusion,EC optimized plant type structure and increased plant lodging resistance.However,the supply of stem carbohydrates to grains was insufficient due to the decrease of LAI,which was not conducive to the formation of grains,resulting in a decrease in kernel number per ear and affecting maize yield.In addition,although EC reduced dry matter weight and nitrogen uptake,EC increased NUtE and HI of maize,which promoted the nutrients utilization efficient and had high production potential.The increase of plant density could mitigate the adverse effects of EC to a certain extent,and then achieve high and stable yield. |
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