| This study was conducted from 2012 to 2014 in experimental farm of Shandong Agricultural University and State Key Laboratory of Crop Biology. Two cultivars Zhengdan 958(ZD958) and Denghai 605(DH605) were used as experimental materials. The ambient sunlight treatment was used as control(CK) and shading treatments(40% of ambient sunlight) were applied at different growth stages from silking stage(R1) to physiological maturity stage(R6)(treatment S1), from the sixth extended leaf stage(V6) to R1(treatment S2) and from seeding to R6(treatment S3). Increasing light from silking stage to maturity stage(L) was also arranged. Root growing development and yield formation of summer maize were investigated to provide the corresponding control measures and provide theoretical references for summer maize cultivation to adapt to the current decreasing light conditions. Main results were as follows:1. Effects of different light condition treatments on grain yield and yield components of summer maize.Light had significant effects on the grain yield of summer maize, the grain yield in response to different light condition treatments showed: L>CK>S2>S1>S3. Grain yield of S1, S2 and S3 were 62.5%, 26.5% and 80.9% lower than CK, while that of L was 11.4% greater than CK. The 1000-grain weight, kernels per ear and harvest ear number per hectare of S1decreased by 20.5%, 41.9% and 21.1% compared to CK; those of S2 decreased by 8.6%, 15.3% and 6.8%; those of S3 decreased 35.4%, 69.6% and 28.8%. The 1000-grain weight and the kernels per ear of L increased 5.5% and 5.1%. These indicated that shading from silking stage to physiological maturity stage had greater effect on the kernel formation of summer maize than shading from the sixth extended leaf stage to silking stage, and increasing light from silking stage to physiological maturity stage increased the grain yield significantly.2. Effects of different light condition treatments on photosynthetic characteristics and dry matter accumulation and distributionPhotosynthetic rate(Pn), transpiration rate(Tr) and stomatal conductance(Gs) decreased significantly and the intercellular CO2 concentration(Ci) increased after shading and photosynthetic rate, transpiration rate and stomatal conductance increased and the intercellular CO2 concentration decreased after increasing light. The dry matter accumulation of summer maize increased with growth stage and reached a maximum at R6 stage. The percentage of dry matter accumulation in vegetative organs decreased, while that in grain increased with growth stage. The dry matter accumulation decreased after shading from silking stage to physiological maturity stage, while that increased after increasing light condition. The percentage of dry matter accumulation in the grain after shading and increasing light were 27.9% and 48.8% respectively.3. Effects of different light condition treatments on nutrient absorption of summer maizeNutrition absorption of summer maize after flowering stage showed: N>K>P. N uptakes of summer maize after flowering stage focused on the initial 30 days, and K did the initial 20 days. The total accumulation N, P and K after anthesis of shading from silking stage to physiological maturity stage decreased by 42.1%, 36.9%, 58.6% and those of increasing light silking stage to physiological maturity stage increased by 36.6%, 27.7%, 33.7%. The N, P and K relative amount of different treatments increased because the reduce degree of dry matteraccumulation of different light condition treatments were higher than that of N and P absorption after shading.4. Effects of different light conditions on grain filling and endosperm cell proliferation of summer mazie.Light affected grain filling significantly. The days of maximum grain filling rate appeared later after shading. Both grain filling rate and weight of maximum grain filling rate also decreased, while those increased after increasing light. The maximum grain filling rate of S3, S2, S1 decreased by 33.0%, 7.0%, 20.4% and that of L increased by 11.0%.There was obvious decline of dry matter accumulation of embryo and endosperm after shading from silking stage to physiological maturity stage compared to control, while the embryo/endosperm ratio increased. The content of starch decreased in endosperm cell after shading and the endosperm cell plumpness decreased. The endosperm cell number of the grain after shading decreased significantly. Effect of S3 on endosperm cell number was the most, while S2 was the smallest. At maturity stage(R6), the endosperm cells number of S3, S2, S1 decreased by 40.0%, 5.3%, 38.7%. After increasing light condition treatment the dry matter accumulation of embryo and endosperm increased, the endosperm cell plumpness increased because of the increase of starch content in endosperm cell.5. Effects of different light conditions on root characteristics of summer maize.5.1 Root dry weight and root/shoot ratioRoot dry weight and root/shoot ratio of summer maize showed: L>CK>S2>S1>S3 under different light condition treatments, namely the root dry weight and root/shoot ratio of summer maize decreased after shading and the root dry weight and root/shoot ratio of S3, S2, S1 at milk-ripe stage(R3) decreased by 44.5%, 9.4%, 29.6% and 29.5%, 9.8%, 16.0%. The root dry weight reduce degree of summer maize in the upper soil layer(0-30 cm) was greater than that in the lower soil layer(30-60 cm) after shading. After increasing light, the root dry weight and root/shoot ratio increased by 49.1% and 11.9%.5.2 Root morphologyShading reduced root length density and root diameter significantly, and effects of S3 on root length density and root diameter were the most, while effects of S1 took the second place and effects of S2 were the smallest. There was no significant difference between S2 and CK at R6 stage because more photosynthate distributed to root after regaining normal light. The root length density and root diameter reduce degree of summer maize in the upper soil layer(0-30 cm) was greater than that in the lower soil layer after shading. The root diameter in the upper soil layer under shading condition had no significant difference with that under normal light condition. The root grown very well after increasing light, the root length density and root diameter increased significantly compared to CK which were helpful for the healthy and strong root system.5.3 Root activityShading reduced root absorption area and root activity absorption area significantly, S3 affected very much, S1 affected less and S2 affected the least. After regaining normal light, the root absorption area of S2 was greater than that of S1, but smaller than that of CK, which indicated that the light after flowering could promote the root absorption area but it could not be recovered to normal. The decrease of root absorption area and root activity absorption area in 0-30 cm soil layer was greater than that in 30-60 cm soil layer, this was because the root environment was relatively stable with soil deeper, which enhanced the resistance of maize, prolonged the root activity time and delayed the root senescence. The absorptive capacity of the root system after increasing light was enhanced, the root absorption area and the root activity absorption area increased significantly and plant would absorb more water and nutrient from soil by the healthy and strong root system to supply the growth of above ground. |
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