Response Of Maize Growth To Light Intensities Under Different Plant Densities

Light condition is an important factor affecting maize growth.The solar radiation resource in west of China is more abundant than that in the east,and the maize plant density and grain yield in the west are generally higher than those in the east.The aim of this study were to ascertain how the maize yield,yield attributes,dry matter accumulation,and leaf area distribution respond to the light intensities;analysis the principle of regional allocation of light resources and maize high-yield population;build up quantitative design methods for high yield population of Maize in different ecological regions;radicate the dynamic index of high-yield population;construct high-yielding populations of maize which adapt to different regional light conditions.This study was divided into three levels.The first level was from 2009 to 2015,the density experiment was implemented in 28 experiments sites whose belong to 9 provinces of China.Analyzed the relationship between the optimum plant density,the optimum LAI and the accumulated solar radiation in different areas.Studied the key meteorological factors that affect maize growth,and providing references for rational planting of maize in different areas.The second level was carried out density experiment in Gongzhuling?Jilin Province,China?,Yinchuan?Ningxia Hui Autonomous Region,China?,and Qitai?Xinjiang Uygur Autonomous Region,China?from 2013 to 2015.The same cultivar and plant density were implemented at the three sites and the crop management practices were optimized for each location.The relationship which under the optimum conditions between the optimum plant density and the corresponding LAI,dry matter accumulation and the climatic factors were analyzed.The third level was to intensive study the mechanism of the effect of light factor on maize growth and construct rational group structure.2015 and 2016,the shading experiment was carried out in Yinchuan and Qitai.The light distribution in maize canopy,the dynamic variations of leaf area,dry matter accumulation,and the variation of yield and its components those were under different irradiance were intensive analyzed.The main results as follows:1 Matching relationship between solar radiation and the optimum plant density among regions.The response of optimum plant density and the corresponding LAI to the solar radiation which accumulated within the maize growth stage showed two different modes and the 1300MJ m^-2?approximate value?was the turning point.In the areas which solar radiation?which accumulated within the maize growth stage?were more than1300 MJ m^-2,the relationship between the optimum plant density and LAI and the solar radiation could be expressed by the formula y=0.19x-186.13(x>=1303.4MJ m^-2)and y=0.012x-10.6(x>=1290MJ m^-2),respectively;in the areas which solar radiation were less than 1300 MJ m^-2,the relationship between the optimum plant density and LAI and the solar radiation could be expressed by the formula y=64.8 and y=8.72-0.003x(x<1290MJ m^-2),respectively.These formulae reflected that the relationship between the optimum plant density and the solar radiation conformed to the linear and platform trend,in other words,when the solar radiation was less than 1300 MJ m^-2 the optimum would be almost constant,when the solar radiation was more than 1300 MJ m^-2 the optimum would increase significantly as the solar radiation increase.In the areas with relatively insufficient solar radiation(less than 1290 MJ m^-2)the optimum LAI would be decrease as the solar radiation increase;in the areas with sufficient solar radiation(more than1290 MJ m^-2)the optimum LAI would increase with the solar radiation increase.The above formulae were proved to be reliable.It is estimated that the current plant density of maize in China has yet to be improved.However,different plant density increasing measures should be adopted in different areas of solar radiation.2 Effects of climatic conditions on the optimum plant density of maize in different areas.Climatic factors significantly influence maize growth and development.Grain yield in this study was significantly positively related to accumulated solar radiation?r=0.93?,diurnal temperature range?r=0.96?,and the number of growing days?r=0.96?during the entire growing season.The three experimental sites had different climatic conditions and therefore different optimum plant densities.The optimum plant densities were 12 plants m^-2 at Qitai,10.5 plants m^-2 at Yinchuan and 7.5 plants m^-2 at Gongzhuling.At the optimum plant density,the LAIs at silking and physiological maturity were,respectively,8.94 and 4.27 at Qitai,7.50and 1.85 at Yinchuan,and 6.18 and 1.67 at Gongzhuling.3 Effects of shading on maize grain yield and dry matter production.On the whole,the yield of maize decreased after shading.Different cultivars and different locations showed different variation characteritics.At Qitai experiment site,under the condition of low shading level?shading 15%?,there were no significant difference found between the yield of xianyu 335?XY335?at the plant density 12,10.5,7.5×10⁴ plants ha^-1 and the corresponding control.Under the same shading level,the yield of zhengdan 958?ZD958?at the plant density 7.5×10⁴ plants ha^-1 was not significantly different from the control.At Yinchuan,the yield of shading treatments decreased significantly compared to the control.Shading mainly affected maize yield by affecting grain number per ear and ear number.Shading had little effect on maize 1000-kernel weight.In terms of yield level,XY335 is more resistant to shading.Shading affected maize dry matter accumulation and allocation.The dry matter accumulation with shading 15%was not significantly different from the control but significantly higher than that of shading 30%and 50%.The post-silking dry matter accumulation and its percentage in the total dry matter accumulation decreased with the increasing of shading level.Compared with other treatments,the shading 50%had significantly lower harvest index?HI?.The overall variation trend of the two cultivars was similar.4 Effects of shading on light and nitrogen distribution within the canopy of maize.The maize population LAI decreased with the increasing of shading level and the performance of the lower leaves was more prominent.The change of LAI caused the change of light distribution within the canopy.Compared with the silking stage,the upper canopy light interception ratio of grain filling stage increased.At the 12×10⁴ plants ha^-1 treatment,the layer of the maximum light interception ratio with shading 50%was higher than that of control.At silking stage,the SLN?specific leaf nitrogen?of the middle and upper layer leaves were significantly higher than the lower leaves.The SLN of each layer decreased with the increasing of plant density.This corresponded to the distribution of light in the canopy.The SLN in maturity stage was lower than that in silking stage.Compared among the shading treatments at the same density,the SLN in the low layer leaves decreased with the increasing of shading level.The trend was same as the grain N content variation but oppositely with the grain N concertation variation.5 Effects of shading on physiological characteristics in ear leaves of maize.Changes in light intensity caused changes in net photosynthesis rate?Pn?,transpiration rate?E?,stomatal conductance?Gs?,internal CO² concentration?Ci?of maize ear leaves.Compared among shading levels at the same plant density,Pn,E,and Gs decreased with the increasing of shading level.Compared among plant density treatments with the same shading level,the degree of declining at high plant density was higher than that of lower plant density.Compared among shading levels at the same plant density,the Ci increased with the increasing of shading level.Compared with XY335,the photosynthetic gas exchange parameters of ZD958 were more sensitive to changes in light intensity.After shading,with the increasing of shading level,the ability of cleaning out active oxygen?SOD,POD,CAT?was depressed,and the MDA content was increased.