种植密度对夏玉米根系特性及氮肥吸收的影响

【目的】玉米是中国第一大粮食作物,在国家粮食安全中具有举足轻重的作用。选用耐密型品种,增加种植密度是现在玉米获得高产的主要措施之一。然而,高密度种植加剧了玉米生长空间的压力,导致单株生长受到抑制,单株产量降低。根系作为吸收土壤水分与养分的主要器官,其生长受密植条件抑制。研究夏玉米品种根系特性对密度响应的基因型差异,探明密植条件下耐密型夏玉米根系特性与氮素吸收、利用的关系,为耐密型夏玉米品种的根系改良及密植条件下养分与水分管理提供依据。【方法】试验于2014—2015年在山东农业大学黄淮海区域玉米技术创新中心进行,以耐密型品种郑单958(ZD958)和不耐密型品种鲁单981(LD981)为试验材料,采用土柱栽培与~(15)N标记技术相结合的技术手段,研究不同种植密度下(D1,52 500 plants/hm~2与D2,82 500 plants/hm~2),不同耐密型品种根系性状及氮素吸收利用情况对种植密度的响应。【结果】增加种植密度可显著提高夏玉米籽粒产量,但两品种单株籽粒产量均显著降低。两品种根系生物量、根长、根系表面积、根系活性吸收面积均随种植密度的增加而降低;D1条件下,LD981根系各项指标生育前期高于ZD958,乳熟期后均低于或显著低于ZD958。D2条件下,两品种根系各项指标生育前期差异不显著,而生育后期LD981显著低于ZD958;地上部单株绿叶面积与穗位叶净光合速率受基因型及密度影响,变化趋势与根系一致。两品种根冠质量比受密度增加影响差异不显著,但根冠活性面积比显著降低;增加种植密度两品种单株氮素积累量及氮利用效率显著降低,肥料氮回收率、氮肥偏生产力均显著提高,但肥料氮所占植株氮素积累量的比例不受密度变化影响;D2下ZD958植株肥料氮含量、肥料氮所占比例、肥料氮回收率及氮肥偏生产力显著高于LD981。【结论】耐密型品种ZD958根系受密度影响较小,高密度下,能够维持相对较高的根量、根长、根系吸收面积及根系活力,且高值持续期长,生育后期衰老缓慢,保证了植株对氮素吸收,有利于地上部进行光合生产、获得较高籽粒产量;高密度下ZD958籽粒库容较高、库调节能力较强,是其氮利用效率及氮肥偏生产力显著高于LD981的主要原因。

Effects of Planting Density on Root Characteristics and Nitrogen Uptake in Summer Maize

【Objective】Maize is the first food crop in China, which plays an important role in national food security. Using density-tolerance hybrids and increasing plant density is one of the primary measures to achieve high yields of maize in modern times. However, the high planting density increased the pressure of maize growth space, resulting in the growth of single plant inhibited and the yield per plant decreased, at the same time, as the major organ to absorb moisture and nutrients from soil, the roots'' growth can be inhibited by high plant density. To ascertain the relationship between the root characteristics of density-tolerance hybrids and grain yield, and nitrogen utilization under high plant density is the base of studying the genotype differences of root characteristics of different summer maize hybrids to plant density, and which is significant for root improvement of density-intolerance hybrids and management of nutrients and moisture under high planting density.【Method】This experiment was conducted during 2014-2015 at the Huanghuaihai Regional Corn Research Center of Shandong Agricultural University. With Zhengdan 958 (ZD958, density-tolerance hybrid) and Ludan 981 (LD981, density-intolerance hybrid) as the experimental materials, using the soil column culture in combination with the ¹⁵N-labeling technique, the responses of root characteristics, as well as nitrogen uptake and utilization, of different density-tolerance varieties to increased density were investigated at two planting densities (D1, 52 500 plants/hm² and D2, 82 500 plants/hm²). 【Result】Grain yield of maize significantly increased with the increase of plant density, while the grain yield per plant of both hybrids significantly reduced. Over the growing process of both hybrids, the root biomass, length, surface area and active absorbing area of both hybrids were decreased with the increase of plant density. In D1 treatment, all root indicators of LD981 were higher than those of ZD958 at early growth stage but then turned to be lower or significantly lower than ZD958 after milk stage. In D2 treatment, no significant differences in various root indicators were observed between the two hybrids at early growth stage; however, the root indicators of LD981 were significantly lower than those of ZD958 at late growth stage. The leaf area per plant and net photosynthetic rate of ear leaf changed in a trend consistent with that of roots. The difference in root-shoot ratio in biomass under the impact of density increase was not significant between the two hybrids; but their root-shoot ratio in active area was significantly reduced. The N accumulation amount (NAA) per plant and N use efficiency (NUE) of both hybrids were significantly reduced, but the N fertilizer recovery rate (NRR) and the nitrogen partial factor productivity (NPFP) significantly improved with plant density increased. In addition, the proportion of N from fertilizer in NAA was not affected by the changes of density. In D2 treatment, the N content per plant, ratio of fertilizer N, NRR and NPFP of ZD958 were significantly higher than LD981. 【Conclusion】The roots of ZD958 proved to be less affected by plant density. At high density, it could maintain relatively high root weight, length, absorbing area and activity, and longer high value duration, which were beneficial to N uptake, the photosynthetic production and obtaining higher grain yield. This suggests that the well-developed roots can guarantee the plant nitrogen uptake at high density, contributing to the photosynthetic production of the aboveground part and thus achieving higher grain yield. The bigger seed set and stronger seed set adjustment ability of ZD958 promoting nitrogen were the primary reason of its higher NUE and NPFP than LD981 at high plant density.