不同株型玉米冠层光氮分布、衰老特征及光能利用对增密的响应

【目的】探究增密对不同株型玉米冠层光氮分布、衰老特征、及其对光能利用及产量的影响,为陕西春玉米高产高效栽培提供支撑。【方法】于2017—2018年以陕单609（紧凑型）和陕单8806（平展型）为试验材料,设置4个种植密度（45 000、60 000、75 000和90 000株/hm²）,测定了冠层光氮分布、叶片衰老、物质生产、光能利用及产量构成等指标。【结果】陕单609和陕单8806分别在90 000株/hm²（13 824 kg·hm^-2）和60 000株/hm²（9 566 kg·hm^-2）达到了最高产量,与45 000株/hm²相比,90 000株/hm²下陕单609和陕单8806的穗粒数（17.8%和30.1%）和百粒重（15.2%和19.6%）均降低。同一密度下,2个品种的冠层光能截获率和叶片氮素浓度表现为上层>中层>下层,随着密度的增加,2个品种冠层上部光能截获率和叶片氮素浓度不断增加,中层和下层的光能截获率和叶片氮素浓度不断下降,当密度增至90 000株/hm²时,陕单8806冠层中部和下部的光能截获率分别较陕单609低8.8%和70.6%,且陕单609中层和下层的叶片氮素浓度较陕单8806高16.0%和40.5%。当密度从45 000株/hm²增至90 000株/hm²,陕单609和陕单8806成熟期相对绿叶面积分别降低36.4%和63.3%,叶片平均衰老速率分别增加40.2%和34.6%,冠层不同层次叶片衰老启动的时间顺序为下层>上层>中层,与陕单8806相比,90 000株/hm²下陕单609生育后期冠层中上部的绿叶面积较高,且下层维持较高的绿叶面积。随种植密度的增加,吐丝前后的氮素吸收量和氮收获指数显著增加,当密度增至90 000株/hm²时,陕单609吐丝前后的氮素吸收量、氮收获指数分别较陕单8806高23.5%、43.9%、12.7%。增密后生物产量、收获指数、冠层光能截获量和光能利用率显著增加,密度增至90 000株/hm²时,陕单609的生物产量、冠层的光合有效辐射、光能利用率和收获指数分别较陕单8806高26.1%、10.2%、9.1%和14.8%。【结论】与陕单8806比,紧凑玉米陕单609密植下较好协同优化冠层光氮空间分布,增加了群体花后中下部光能截获量,延缓群体冠层花后中下层叶片衰老,促进群体花后干物质和氮素积累,获得更高的籽粒产量和光能利用率。

Responses of Canopy Radiation and Nitrogen Distribution,Leaf Senescence and Radiation Use Efficiency on Increased Planting Density of Different Variety Types of Maize

【Objective】The objective of this experiment was to study the effects of planting density on canopy senescence, radiation use efficiency and yield of different plant types maize, so as to provide technical support for cultivation of high yield and high efficiency of spring maize in northern Shaanxi. 【Method】 In 2017 and 2018, the field experiments were conducted by using two maize hybrids, including Shaandan 609 (compact) and Shaandan 8806 (flat), with four planting density treatments, including 45 000, 60 000, 75 000 and 90 000 plants/hm². Canopy light and nitrogen distribution, leaf senescence, nitrogen accumulation, dry matter production, radiation use efficiency and yield components were determined. 【Result】 Shaandan609 and Shaandan8806 reached the highest grain yield at 90 000 plants/hm² (13 824 kg·hm^-2) and 60 000 plants/hm² (9 566 kg·hm^-2), respectively. Compared with 45 000 plants/hm², the average kernels per ear (17.8% and 30.1%) and 100-kernels weight (15.2% and 19.6%) of Shaandan609 and Shaandan 8806 both reduced under 90 000 plants/hm². The canopy light interception and leaf nitrogen concentration of the two varieties showed: the upper layer>the middle layer>the lower layer. With the increase of planting density, the fraction of the photosynthetically active radiation interception (FIPAR) and leaf nitrogen concentration increased at upper layer, but decreased at the mid and lower layer. When the density increased to 90 000 plants/hm², the FIPAR at middle and upper canopy and the lower canopy of Shaandan 8806 were 8.8% and 70.6% lower than Shaandan 609, respectively, and the leaf nitrogen concentration at middle and upper canopy layer and lower canopy of Shaandan 609 were 16.0% and 40.5% higher than Shaandan 8806. When density increased from 45 000 plants/hm² to 90 000 plants/hm², the relative green leaf area at maturity (RGLA_m) decreased by 36.4% and 63.3%, respectively, while the mean rate of decrease in RGLA (V_m) increased by 40.2% and 34.6%, respectively. The sequence of date of onset of leaf senescence (T_s) was as follows: the lower layer>the upper layer>the middle layer. Compared with Shaandan 8806, the green leaf area was higher in the middle and upper layer of Shaandan 609, and maintained a higher green leaf area at the lower layer during the later growth stage under 90 000 plants/hm². With the increasing of planting density, the nitrogen uptake during the pre-silking (Npre) and post-silking (Npost), and nitrogen harvest index (NHI) increased significantly. When the density increased to 90 000 plants/hm², Npre, Npost and NHI of Shaandan 609 were 23.5%, 43.9% and 12.7% higher than Shaandan 8806, respectively. The biomass yield (BM), intercept photosynthetically active radiation (IPAR) and radiation use efficiency (RUE) increased significantly when improved plant density. When the density increased to 90 000 plants/hm², the BM, IPAR, RUE and HI of Shaandan 609 were 26.1%, 10.2%, 9.1% and 14.8% higher than Shaandan 8806.【Conclusion】Compared with Shaandan 8806, the compact maize Shaandan 609 could improve the spatial distribution of light and nitrogen at the middle and upper layer under high density, increased the light intercept at the middle and lower canopy, delayed leaf senescence at the mid and lower canopy, and promoted the dry matter accumulation after silking, so a higher grain yield and RUE were obtained.