玉米是全球也是中国第一大作物，在保障国家粮食安全中占有重要地位。当前，面对经济社会的快速发展和人增地减、资源紧缺、生态环境恶化等一系列突出问题，玉米栽培学科正面临着严峻挑战和新的历史发展机遇，在此重要历史关头，回顾中国玉米栽培研究历程和科技进展，探索未来发展方向具有重要的意义。分析表明，经过60年不懈努力，玉米栽培研究的目标已由产量为主向高产、优质、高效、生态、安全等多目标协同发展，研究内容不断拓宽与深入，形成了具有显著中国特色的玉米栽培科学与技术体系。进入21世纪以来，玉米栽培研究进入黄金发展期，在栽培理论、关键技术创新与应用方面取得一系列重要突破，在保障国家粮食安全中发挥了重要的作用。围绕未来玉米生产对科技的需求，依据现代科技的发展趋势，笔者认为高产、优质、高效、生态、安全仍将是未来玉米栽培研究的主要目标，并提出今后20年重点研究的方向与任务：一是继续探索不同生态区玉米产量潜力及突破技术途径，努力提高单产水平；二是转变生产方式，围绕籽粒生产效率，以提高资源利用效率和劳动生产效率为目标，降低生产成本，提高商品质量，增强玉米市场竞争力；适度发展青贮玉米和鲜食玉米等，促进玉米生产向多元化方向发展；三是应对全球气候变化，开展抗逆、减灾、稳产理论和技术研究，实施保护性耕作，实现玉米可持续生产；四是依托现代信息技术，开展智能化栽培技术研究，实现玉米精准生产与管理；五是强化栽培学科基础研究，玉米设计栽培，夯实玉米科技研究和生产发展基础。

【目的】探究密度与氮肥用量对不同耐密型夏玉米品种籽粒产量及氮素利用效率的影响。【方法】以稀植大穗型品种鲁单981（LD981）和紧凑耐密型品种郑单958（ZD958）为供试材料，设置52 500和82 500 株/hm²两个种植密度，同时设置0、90、180、270和360 kg·hm^-25个施氮水平，研究密度与氮肥用量对不同耐密型夏玉米品种单株及群体干物质积累特性、氮素转运效率、氮素利用效率、产量及其构成因素的影响。【结果】增加种植密度，相同施氮水平处理的千粒重和穗粒数显著降低，单位面积穗数、空秆率、倒伏率显著提高，不耐密品种空秆率、倒伏率增加更显著。其中，ZD958与LD981各施氮处理的平均千粒重、穗粒数分别降低6.24%、6.77%和7.52%、18.09%，LD981空秆率、倒伏率高达17.0%、27.6%，显著高于ZD958。高密度条件下，籽粒产量随施氮量增加而增加，施氮270和360 kg·hm^-2处理的产量差异不显著；低密度条件下，随施氮量增加，籽粒产量先上升后下降，施氮量270 kg·hm^-2处理产量达到最大值。增加种植密度，夏玉米单株干物质积累量呈降低趋势，群体干物质积累量呈增加的趋势。随施氮量增加，单株和群体干物质积累量均显著增加，花后干物质贡献率呈上升趋势。相同氮素水平下，高密度处理显著提高夏玉米总氮素积累量、氮素转运量及其对籽粒的贡献率。增加种植密度，ZD958和LD981各施氮处理的平均总氮素积累量、氮肥农学利用率、氮肥利用率分别增加15.94%、39.01%、26.22%和1.96%、5.79%、14.92%。相同种植密度水平下，总氮素积累量和花后氮素同化量随施氮量增加呈上升趋势，而氮肥农学效率、氮肥利用率和氮肥偏生产力呈下降趋势。增加种植密度，营养器官氮素转运量和氮素转运对籽粒的贡献率显著增加。高密度种植条件下，氮素转运效率及贡献率随施氮量增加而增加，而低密度种植条件下，随施氮量增加而降低。【结论】本试验条件下，增密施氮显著提高不同耐密型夏玉米干物质积累量，但密度对籽粒产量的影响，品种间差异显著。增密后，LD981 籽粒产量增加不显著，ZD958 籽粒产量显著提高。高密度条件下，增加施氮量，不同耐密型玉米籽粒产量均显著增加，而 LD981 空秆率、倒伏率显著提高，是限制 LD981 籽粒产量提高的主要原因。增密显著提高不同耐密型玉米氮素利用率，提高营养器官氮素转运量；增加种植密度，ZD958 花后氮素同化量增加，LD981 则降低。施氮降低了植株氮素利用效率，但可以提高高密度条件下植株氮素吸收量，提高花后氮素同化量。增密与施氮相结合，有利于耐密型玉米产量与氮肥利用率协同提高。综合考虑产量和氮效率两方面，ZD958适宜种植密度为82 500株/hm²，施氮量为270 kg·hm^-2；LD981适宜种植密度为52 500株/hm²，施氮量为180 kg·hm^-2。

Many plant species can modify their root architecture to enable them to forage for heterogeneously distributed nutrients in the soil. The foraging response normally involves increased proliferation of lateral roots within nutrient-rich soil patches, but much remains to be understood about the signalling mechanisms that enable roots to sense variations in the external concentrations of different mineral nutrients and to modify their patterns of growth and development accordingly.In this review we consider different aspects of the way in which the nitrogen supply can modify root branching, focusing on Arabidopsis thaliana. Our current understanding of the mechanism of nitrate stimulation of lateral root growth and the role of the ANR1 gene are summarized. In addition, evidence supporting the possible role of auxin in regulating the systemic inhibition of early lateral root development by high rates of nitrate supply is presented. Finally, we examine recent evidence that an amino acid, L-glutamate, can act as an external signal to elicit complex changes in root growth and development.It is clear that plants have evolved sophisticated pathways for sensing and responding to changes in different components of the external nitrogen supply as well as their own internal nitrogen status. We speculate on the possibility that the effects elicited by external L-glutamate represent a novel form of foraging response that could potentially enhance a plant's ability to compete with its neighbours and micro-organisms for localized sources of organic nitrogen.

The plant root system is highly sensitive to nutrient availability and distribution in the soil. For instance, root elongation is inhibited when grown in high nitrate concentrations. To decipher the mechanism underlying the nitrate-induced inhibition of root elongation, the involvement of the plant hormone auxin in nitrate-dependent root elongation of maize was investigated. Root growth, nitrogen and nitrate concentrations, and indole-3-acetic acid (IAA) concentrations in roots and in phloem exudates of maize grown under varying nitrate concentrations were analyzed. Total N and nitrate concentrations in shoots and roots increased and elongation of primary, seminal and crown roots were inhibited with increasing external nitrate from 0.05 to 5mM. High nitrate-inhibited root growth resulted primarily from the reduced cell elongation and not from changes in meristem length. IAA concentrations in phloem exudates reduced with higher nitrate supply. Inhibition of root growth by high nitrate was closely related to the reduction of IAA levels in roots, especially in the sections close to root tips. Exogenous NAA and IAA restored primary root growth in high nitrate concentrations. It is concluded that the inhibitory effect of high nitrate concentrations on root growth may be partly attributed to the decrease in auxin concentrations of roots.

【目的】研究密度对高产玉米（＞15 000 kg•hm-2）产量及其构成因子的影响，揭示高产玉米产量形成机制，为玉米持续稳定高产提供依据。【方法】连续两年在新疆和宁夏高产玉米区，以郑单958为试材，以1.5万株/hm2为一个密度梯度，设置从1.5万株/hm2至18万株/hm2不同密度处理，充分满足水肥需求，进行高产栽培实践，在实现高产基础之上分析其产量及产量构成因子特征。【结果】两年多点共68个处理，最低和最高单产分别为7 675.5和20 503.5 kg•hm-2，其中有47个处理达到15 000 kg•hm-2以上的产量；对产量构成特征的分析表明，要达到15 000 kg•hm-2以上的高产，最低、最高密度分别为5.25万株/hm2和16.28万株/hm2；最低、最高收获穗数分别为6.66万穗/hm2和13.84万穗/hm2；最低、最高穗粒数分别为365和657粒；最低、最高千粒重分别为237和404 g。【结论】密度与单产呈抛物线关系，以10.5万株/hm2密度处理单产最高；随着产量的提高，种植密度、单位面积穗数、穗粒数和千粒重表现出最适值范围变窄的趋势。随种植密度增加，单位面积穗数呈增加趋势，穗粒数和千粒重呈下降趋势，而单位面积粒数呈增加并趋于不变趋势。

【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¹⁵N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/hm²与D2，82 500 plants/hm²），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。

Increasing evidence shows that partial nitrate nutrition (PNN) can be attributed to improved plant growth and nitrogen-use efficiency (NUE) in rice. Nitric oxide (NO) is a signalling molecule involved in many physiological processes during plant development and nitrogen (N) assimilation. It remains unclear whether molecular NO improves NUE through PNN. Two rice cultivars (cvs Nanguang and Elio), with high and low NUE, respectively, were used in the analysis of NO production, nitrate reductase (NR) activity, lateral root (LR) density, and (15)N uptake under PNN, with or without NO production donor and inhibitors. PNN increased NO accumulation in cv. Nanguang possibly through the NIA2-dependent NR pathway. PNN-mediated NO increases contributed to LR initiation, (15)NH₄(+)/(15)NO₃(-) influx into the root, and levels of ammonium and nitrate transporters in cv. Nanguang but not cv. Elio. Further results revealed marked and specific induction of LR initiation and (15)NH₄(+)/(15)NO₃(-) influx into the roots of plants supplied with NH₄(+)+sodium nitroprusside (SNP) relative to those supplied with NH₄(+) alone, and considerable inhibition upon the application of cPTIO or tungstate (NR inhibitor) in addition to PNN, which is in agreement with the change in NO fluorescence in the two rice cultivars. The findings suggest that NO generated by the NR pathway plays a pivotal role in improving the N acquisition capacity by increasing LR initiation and the inorganic N uptake rate, which may represent a strategy for rice plants to adapt to a fluctuating nitrate supply and increase NUE.© The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.