弱光胁迫影响玉米产量形成的生理机制及调控效应

孙智超 张吉旺

综述

弱光胁迫影响玉米产量形成的生理机制及调控效应

孙智超 张吉旺*

山东农业大学农学院 / 作物生物学国家重点实验室, 山东泰安 271018

在全球气候变化背景下, 生育期内光照不足已成为制约玉米产量提高的主要因素之一, 增加了全球粮食生产和营养安全的风险。本文从光合性能、养分吸收特性、籽粒形成与灌浆特性等方面系统总结了弱光胁迫影响玉米产量形成的生理机制。弱光降低了叶片捕光能力, 基质和基粒类囊体结构解体, 相关酶活性降低, 光系统受到损伤, 碳同化能力降低, 进而抑制根系发育, 影响根系形态和功能, 不利于养分吸收和代谢。由于营养供应不足, 雌、雄穗发育受阻, 花粉和花丝的形态功能受到影响, 导致小花受精率低, 穗粒数降低。弱光条件下, 胚乳细胞数量——“库”容量降低, 胚乳传递细胞结构和功能受到影响, 内源激素平衡被打破, 蔗糖-淀粉代谢相关酶活性下降, 茎节维管束数目和面积减少, 物质转运和转化能力降低, 导致淀粉充实状态差, 粒重降低。因此, 为缓解弱光胁迫对玉米产量形成的影响, 亟须创建系统评估耐阴品种的指标, 利用现代育种技术加快培育出高光效耐阴新品种, 采取增施氮肥、去除顶部叶、喷施生长调节剂和叶面肥等栽培措施提高产量。未来研究需要注重根冠协调, 深入探讨弱光胁迫的作用机理, 为玉米抗逆增产关键技术的创建提供理论依据。

弱光胁迫; 人工遮阴; 玉米; 产量; 耐阴性; 生理机制; 调控效应

玉米作为我国第一大粮食作物, 在农业生产和经济发展中发挥着重要作用。光是玉米生长发育不可或缺的气候因子, Chen等[1]研究表明, 太阳辐射每减少1 MJ m−2, 玉米产量降低6%～7%。但近年来由于气候变化等因素, 玉米生育期内日照时数平均降低13%, 太阳辐射平均降低4% (图1, 中国气象数据网, http://data.cma.cn/)。光照不足将成为未来粮食产量进一步提高的重要限制因素。

弱光胁迫对玉米的光合特性、养分吸收特性、籽粒形成与灌浆特性等均有显著影响, 导致产量降低。前人通过人工遮阴的方式模拟寡照天气, 以探究弱光胁迫影响玉米产量形成的生理生态机制。本文主要从大田中模拟弱光胁迫的方法、弱光胁迫影响玉米产量形成的生理机制、提高产量的途径和未来研究展望4个方面进行综述, 以期为耐阴玉米品种选育和应对弱光胁迫关键技术的创建提供科学依据。

1 大田弱光研究方法

前人针对不同的研究对象(单株或群体)和研究内容, 选用的材料和遮阴方式也不同(图2)。Earley等[2]使用木框和金属片来探究产量与遮阴度的关系; Struik[3]、Kiniry等[4]、赵久然等[5]和张吉旺等[6]利用遮阴网以明确弱光胁迫影响产量形成的关键生育时期; Takayuki等[7]通过盆栽试验探索生育后期叶片相互遮挡导致弱光的再适应能力(图2)。人工遮阴试验能否实现遮光处理的唯一差异性尤为重要, 但目前部分试验条件由于一些原因未能实现单一光照变量,主要有以下几点: 不同的遮阴方式产生不同的气候条件, 当用遮阴网把玉米植株的一半或全部覆盖, 其内部的温度和CO2浓度会有所差异; 木框、聚丙烯、聚乙烯、棉布、铝箔纸、尼龙等遮阴材料的材质和颜色不同, 容易改变入射光光质, 影响植株形态; 当试验面积不足时, 随着光照角度不断偏移, 相同处理的植株受光条件不一致, 取样植株不具有代表性; 当遮阴设备的宽度和高度无法满足机械耕作要求时, 人工整地的深度不足, 土壤质量变差, 影响作物根系下扎。

因此, 建议大田遮阴试验在面积较大、土壤理化性质一致的地块上进行, 采用透光率稳定、不改变光质和质量良好的遮阴网, 搭配可拆卸、可升降的支撑架组成遮阴设备。其中遮阴网的覆盖方式应当不改变作物田间气候, 以达到最大程度地模拟自然弱光环境, 尽可能实现光照强度或者光照时间改变的唯一差异性, 增加试验结果的可信度与一致性。

图1 6月至10月的日照时数(1961−2018年)和总太阳辐射(1961−2020年)

2 弱光胁迫影响玉米产量形成的生理机制

2.1 光合特性

光合作用包括原初反应、电子传递、碳同化等步骤, 是玉米干物质积累最基本的方式, 也是对环境变化最敏感的代谢过程。不同于高温等氧化胁迫带来的伤害, 弱光胁迫对光合性能的影响在于结构形成。由于光照不足, 单位叶面积的叶肉细胞和叶绿体数量减少, 内部类囊体结构部分解体, 基粒类囊体数量减少且排列疏松, 片层松散[12](图3-a～d)。位于类囊体膜上的叶绿素等聚光色素含量降低[13], 导致叶片捕光能力降低。叶绿素尤其是叶绿素含量降低可能与参与卟啉和叶绿素代谢基因下调有关[14]。反应中心色素含量减少, 氧化激发出的电子也相应减少。弱光胁迫显著下调玉米光系统II中的、、、和, 光系统I中的, 细胞色素复合体b6/f中的等基因[14], 导致反应中心亚基及电子受体数量减少。两系统间电子传递受阻, 光化学效率降低[15-17]。

在暗反应中, 磷酸烯醇式丙酮酸羧化酶(phosphoenolpyruvate carboxylase, PEPC)相关基因表达易受光强影响[18], 核酮糖-1,5-二磷酸羧化酶(ribulose-1,5-bisphosphate carboxylase/oxygenase,Rubisco)的活化又受限于依赖光照的三磷酸腺苷(adenosine triphosphate, ATP)[19]。在低光照条件下, Rubisco、PEPC、苹果酸酶(NADP-malic enzyme, NADP-ME)等光合酶活性显著降低[13,20], 光合产物输出减少且速率变慢。并且叶绿体中发现淀粉粒增大[21], 可能是弱光胁迫改变了磷酸丙糖转运蛋白(triose phosphate translocator, TPT)活性, 进而改变了淀粉与蔗糖的合成比例[22], 出现“淀粉阻塞”现象, 减少了对其他器官的蔗糖供应, 限制作物生长。

叶片是植物截获光能的物质载体, 光照不足导致类囊体结构松散、光合酶活性降低, 光合产物供应不足, 降低叶片生长速率和叶面积指数(leaf area index, LAI)[13], 进一步限制光能截获。玉米叶片生长响应差异是光合碳同化能力差异的结果。综合来看, 叶片整体光合性能降低, 干物质积累量不足且向籽粒分配比例减小, 收获指数和产量显著降低[23]。

2.2 养分吸收特性

根系作为最主要的吸收器官, 其功能期长短决定叶片功能期长短。弱光条件下由于干物质供应不足, 根系发育显著受阻(图3-i, j), 根干重、根长度、根表面积、根体积等指标均下降[24-26], 根系直径和根长密度降低[24-26]。根部细胞呼吸作用放出的CO2溶于水后解离出H+和HCO3-离子, 与土壤溶液和土壤胶粒上吸附的离子进行交换。弱光条件下, 根系碳水化合物浓度下降[27], 根系呼吸速率降低[28], 进而改变了离子交换频率, 导致根系总吸收面积与活跃吸收面积显著降低, 根系活力降低[25], 氮、磷、钾吸收量减少[29], 影响植株正常生长发育。

光照不仅影响根系吸收养分的能力, 对土壤养分循环过程也有影响。在土壤-植物系统中, 土壤微生物通过产生多种调节土壤有机质分解的胞外酶来驱动养分循环。弱光胁迫显著改变了根际土壤微生物细菌、放线菌和真菌数量, 抑制了根际土壤中脲酶的活性, 导致土壤氮含量减少[30]。微生物生命活动能力减弱, 对有机物质的分解速度减慢, 有机质含量减少[31]。微生物生命活动能力减弱还会与作物争夺氮素养分, 形成恶性循环。但Zhou等[32]研究报道, 在弱光缺磷条件下, 玉米接受弱光信号并将更多的光合产物以蔗糖的形式分配给根系, 刺激根系生长, 促进根系对磷的吸收, 是玉米适应弱光胁迫的一种表现。

在根系-微生物-土壤微生态系统中, 弱光胁迫改变了土壤中微生物的数量和结构, 各种酶活性降低, 土壤中有效养分的积累减少。由于干物质供应不足, 根系对养分吸收量减少, 进一步影响地上部生长发育, 产量显著降低。但弱光胁迫导致玉米植株养分含量减少的关键是土壤中养分积累与转化能力减弱还是根系吸收养分的过程受到阻碍？其主导因素及相关机制仍应继续研究。为了改善弱光胁迫带来的“养分胁迫”, 植株内部的同化物分配[32]或根系分泌物对有益微生物的招募[33]等适应机制也需深入挖掘, 为培育高效利用养分的新品种提供理论依据。

2.3 籽粒形成与灌浆特性

弱光胁迫显著降低玉米叶片花后干物质生产能力, 且由于碳、氮积累不足[34], 蔗糖转化酶(sucrose invertase, INV)活性较高[35], 蔗糖磷酸酶(sucrose phosphate synthase, SPS)活性较低[36], 叶片直接利用了原本转运到雌、雄穗的同化物, 导致蔗糖输出量减少。因此, 为满足籽粒发育和灌浆需求, 淀粉酶(amylase)和SPS活性增加[37], 促进碳储备从茎向籽粒的再调动, 同化物转运量增加[23,38], 但仍不能弥补吐丝后干物质生产量在光照不足条件下的产量损失。

蔗糖通过维管束长距离运至籽粒, 经珠心突起细胞后通过胚乳转移细胞进入内胚乳, 在蔗糖-淀粉代谢酶作用下合成淀粉。弱光条件下, 穗柄维管束面积未受光照影响[39], 但基部第3茎节的维管束数目显著减少, 中央大维管束的木质部和韧皮部面积减小[40](图3-e～h), 蔗糖流速受限。弱光胁迫使胚乳传递细胞变小, 传递细胞壁内突变稀、变短[39], 不同层次间连接程度下降。线粒体数量减少, 籽粒中提前形成黑层, 导致籽粒胚乳传递细胞功能期提前结束[41]。弱光胁迫不仅减少了运往籽粒的同化物, 而且限制了蔗糖的长距离运输, 导致供给籽粒利用的蔗糖显著降低。

穗粒数由雌、雄穗开花受精特性决定。弱光条件下雌、雄穗发育和授粉受精过程受到显著影响, 穗粒数显著降低。由于同化物供应不足, 玉米控制穗发育的miR156、miR172表达下调[42], 穗原基分化的总小花数减少[42], 雌、雄穗的发育和分化受阻(图3-e, h), 尤其是小花分化时间的延长, 导致花期不遇[43]。花粉由于淀粉粒数目减少, 营养供应不足, 导致萌发孔及其附近严重畸形及内陷(图3-a～d), 萌发率降低[44]。花丝生长速率减慢, 雌雄间隔期延长[43]。弱光胁迫也显著降低花药开裂率[45], 但具体影响方式还需进一步探索。

粒重是由库容大小和库的充实程度共同决定的,胚乳细胞数目反映库容大小, 灌浆特性反映充实程度。到达籽粒的蔗糖经蔗糖合酶(sucrose synthase, SUS)、腺苷二磷酸葡萄糖焦磷酸化酶(adenosine 5' diphosphate glucose pyrophosphorylase, AGPase)、尿苷二磷酸葡萄糖焦磷酸化酶(uridine diphosphate glucose pyrophosphorylase, UGPase)、可溶性淀粉合成酶(soluble starch synthase, SSS)和淀粉分支酶(starch branching enzyme, SBE)等转化为淀粉。植物激素是一种调节植物生长发育的微量活性物质, 各激素协同作用, 共同调节籽粒形成和灌浆。生长素(IAA)、玉米素(ZR)和赤霉素(GA)和适宜的脱落酸(ABA)含量[46-50]与胚乳细胞分化、增殖和籽粒灌浆速率呈显著正相关, 但ABA是一种反馈调节型激素,超过一定值后ABA会产生抑制作用, 导致籽粒灌浆速率变慢[51]。因此, 猜想籽粒中存在一种灌浆通路: 激素在接收蔗糖信号后, 通过控制蔗糖-淀粉代谢酶活性对淀粉合成起作用。喂养蔗糖弥补籽粒损失试验[52]以及淀粉合成酶含量与激素含量的同步变化曲线[53]进一步证明了此观点, 具体调控机制还需进一步探究。弱光条件下, 供给玉米籽粒的蔗糖减少, IAA、GA和ZR含量降低, ABA含量升高[54], 影响胚乳游离核的分裂和增殖[5], 使胚乳细胞数量减少。并且SUS、SSS、AGP、UGP、SBE等酶活性低[39,55], 灌浆高峰持续期与活跃灌浆期缩短, 最大灌浆速率和平均灌浆速率下降[56], 籽粒充实度不足, 粒重显著降低。蔗糖信号如何调控各激素表达以及激素间相互影响的方式还需进一步探究。籽粒中细胞壁转化酶(cell wall invertase, CWI)等活性降低[38], 不利于蔗糖的卸载。综合来看, 弱光条件下籽粒形成与灌浆受阻多由于蔗糖供应不足、运输受阻、卸载困难、利用率低以及库容限制, 其中喂养蔗糖弥补籽粒损失试验[52]进一步证明蔗糖供应不足是影响穗粒数和粒重的主导因素。

同一果穗不同位置的籽粒存在同化物竞争关系,这在一定程度上制约产量的提高。在籽粒形成和灌浆过程中, 上部籽粒的小花分化比中下部滞后[57], 胚乳细胞数目最少[58], ZR和IAA浓度较低, ABA浓度较高[58-59], 蔗糖-淀粉转化相关酶(SSS、AGP、SUS和SBE)活性及峰值较低[46,58-59], 同化物竞争力弱, 产生较多的未灌浆型败育粒和已灌浆型败育粒。目前, 关于逆境对籽粒发育的研究多集中于果穗中部, 对果穗顶部籽粒的研究较少, 未来应重点改善上部弱势粒的授粉结实特性, 进一步挖掘玉米的高产潜力。

综上所述, 弱光胁迫降低了玉米光合作用, 导致后续一系列生理过程缺乏能量和物质供应, 产量显著降低(表1和图4)。光照减少导致叶绿体内部类囊体发育不良, 光系统间电子传递不协调, ATP和[H]无法满足暗反应的需求, PEPC和Rubisco等关键酶活性降低, 同化能力减弱。各器官发育所需的同化物供应不足, LAI减小, 根系形态和功能受到抑制, 吸收养分的效率降低。由于营养供应不足和同化物利用率低, 开花受精过程受到影响, 内源激素平衡被打破, 蔗糖-淀粉转化相关酶活性降低, 胚乳细胞数目减少, 且淀粉合成不足, 籽粒充实度较差。弱光胁迫最终导致穗粒数和粒重降低, 产量显著降低。

图3 自然光照和弱光条件下玉米根、茎、叶、雌穗、雄穗和花粉的对比

a, d: 花粉的淀粉粒数量; b, c: 花粉的外观扫描结构(800×); e, h: 雌雄穗分化进程; f, g: 果穗; i, j: 叶片横切面(200×); A, D: 叶绿体在叶肉细胞内的分布状况(2500×); B, C: 叶肉细胞的超微结构(25,000×); E, H: 第3茎节中心维管束的结构(100×); F, G: 第3茎节小维管束的结构(100×); I, J: 根横切面(100×)。EP: 表皮细胞; MT: 叶肉细胞; N: 细胞核; Ch: 叶绿体; SL: 基质片层; GL: 基粒片层; Mi: 线粒体; CW: 细胞壁; CM: 细胞膜; Spikelet differentiation: 小穗分化期; Filament elongation: 花丝伸长期; Filament maturation: 吐丝期; Sex organ formation: 性器官形成期; Anther development: 花药发育期。本表部分图片引自高佳等[12]、王群等[25]、周卫霞等[43]、崔海岩等[40]、杜成凤等[60]。

a, d: the number of starch grains in pollen; b, c: scanning structure of pollen appearance (800×); e, h: differentiation process of tassel and ear; f, g: ears; i, j: leaf cross-section (200×); A, D: distribution of Chloroplasts in mesophyll cells (2500×); B, C: ultrastructure of mesophyll cells (25,000×); E, H: the structure of central vascular bundle of the third stem segment (100×); F, G: the structure of small vascular bundle of the third stem segment (100×); I, J: root cross-section (100×). EP: epidermal cell; MT: mesophyll cell; N: nucleus; Ch: chloroplast; SL: stroma lamella; GL: grana lamella; Mi: mitochondria; CW: cell wall; CM: cytomembrane. Some images in this picture were quoted from Gao et al.[12], Wang et al.[25], Cui et al.[40], Zhou et al.[43], and Du et al.[60].

表1 不同遮光时期和遮光率对玉米产量造成的损失

(续表1)

图4 弱光条件下可能影响玉米产量形成的生理机制

3 弱光条件下可能提高玉米产量的途径

光合作用产物是形成作物产量的物质基础, 光能利用率是投射到作物表层的光合有效辐射能被植物转化为化学能的比率。在光照不足的情况下, 提高叶片光截获及光能利用效率, 增加光合产物的积累量, 提高同化物向籽粒的转运比例是增产关键。作物的光截获取决于叶片的大小、分布等因素, 增产需要增加叶片截获光照的时间长度和空间宽度。引用生育期长的品种或喷施植物生长调节剂可有效延缓灌浆期叶片衰老速度, 保持冠层结构不变, 充分利用气候资源, 提高潜在产量。Su等[65]研究报道,引种生长季较长的品种可有效提高作物的辐射和热利用率, 提高产量。外源喷施植酶Q9后, 叶片活性氧清除能力提高, 叶片功能期延长, 粒重增加[66-67]。植物生长调节剂和叶面肥是目前促进作物增产的主要措施, 明确其作用机理及作用有效时间, 对后续新产品的施用方式和粘附时间提供理论指导意义。通过“去源”、改变叶夹角等措施可有效改善叶片分布, 优化作物冠层结构, 尽可能减少叶片间的遮挡面积。去除顶部2片叶能显著改善冠层中下部叶片光照环境, 保证籽粒灌浆期间的光合效率, 提高籽粒灌浆速率, 增加产量[68]。优化综合农艺管理措施(栽培方式、种植密度、施肥管理和收获时间)可以调整冠层结构, 增加光截获, 减少光损失[69]。聚合优势耐阴表观性状以获得高光效耐阴新品种是新时期育种的主要目标。Shi等[70]将LAI (品种A)+氮素利用效率(品种B)+叶角等(品种A)+叶片氮含量(品种A) 4个参数组合, 其产量比品种A和B分别提高了24.1%和134.7%。不同品种的耐阴性状不同, 明确玉米各生育时期的物质需求特性, 准确地将不同品种的“耐阴性状”组合在同一品种, 最大限度地利用光照, 达到弥补干物质需求缺口的目标。

太阳光中约有47%不能被叶片吸收, 剩余53%中约有16%的光能不能被叶片充分吸收, 约有9%的光能吸收后在体内不能有效传递, 约有19%的光能由于耗散等方式不能转化为稳定的化学能, 大约仅有4%和5%的光能用于物质代谢消耗和物质积累[71]。弱光胁迫降低玉米叶片光合性能, 光能利用率将会进一步降低。如何改善植株内部光合性能, 提高光能利用率是下一步增产亟须解决的问题。在弱光条件下, 光受体PHOTO2感受光照强度后, 通过调控定位于叶绿体外膜的CHUP1蛋白, 使叶绿体沿垂直于光线的方向贴细胞壁排列, 增加光能的吸收和利用[72]。在叶绿体发育中起着重要的作用, 遮阴处理后叶片表达减少, 影响叶绿体数量和基质片层发育[73]。若将过表达, 对叶绿体发育不良的问题是否有缓解作用？籼稻和粳稻的耐光性差异在于D1蛋白[71], 明确籼稻是如何调控D1蛋白的表达, 对缓解弱光条件下电子传递受阻有重要意义。增加养分供应也间接提高了作物的光合效率。弱光胁迫下玉米接种摩西球囊霉后, 菌丝会从土壤中摄取各种营养元素供玉米生长, 叶片合成叶绿素的能力提高, 捕光能力增强[74]。适量增施氮肥也促进了根系对氮素的吸收, 增加了叶片中叶绿素含量, 提高光合效率[75]。施氮同时增强了硝酸还原酶(nitrate reductase, NR)、谷氨酰胺合成酶(glutamine synthetase, GS)和SPS的活性, 提高碳氮代谢能力, 增加穗粒数和粒重[76]。发挥其他部位的光合作用也是增产的途径之一。大豆豆荚具有与叶片相似的光合场所和功能, 其光合速率可以弥补叶片衰老后光合性能降低的问题[77]。小麦的芒、颖片、内稃和外稃等均具有较完整的叶绿体结构和进行光合作用的能力[71]。挖掘并提高茎、苞叶等器官光合作用的能力, 为实现籽粒多通道物质积累提供可能。Shi等[78]研究表明, 参与耐阴反应的核心基因除了参与光信号传导(FKF1)外, 占比最大的是IAA (IAA16)。外源喷施6-BA提高了玉米籽粒中IAA含量, 促进籽粒中淀粉积累[79]。乔江方等[80]研究报道, 喷施IAA缓解减产效果最好。目前试验结果直接或间接证明IAA对耐阴反应具有主导作用, 但其对胁迫的应答机制还未清楚。若能明确弱光条件下IAA的传递网络和调控位点, 对夏玉米源、流、库限制的改进将有很大可能性。

4 研究展望

近几十年来, 光照时数和太阳辐射的变化趋势表明弱光胁迫已经成为未来影响玉米产量的重要因素之一。综合前人的研究结果, 对未来发展和研究方向有以下思考和建议:

一是深入和系统研究弱光胁迫影响玉米产量形成的生理生态机制。耐阴性通常被描述为植物在弱光条件下继续生存的能力, 理论上分为适应弱光和回避弱光, 但由于位置的固定性, 作物缺乏回避弱光的能力, 对弱光的响应多被归为第一类。例如, 玉米接受弱光信号后, 将更多的光合产物以蔗糖的形式分配给根系, 刺激根系生长, 促进玉米根系对磷的吸收[32]。目前关于玉米适应弱光胁迫的机制报道较少, 未来应深入研究弱光胁迫是如何影响产量形成以及植株内部是如何启动“防御机制”来适应弱光。作物生长需要地上部与地下部的协同发展, 但目前研究多集中于地上部, 关于地下部以及整株联动的研究鲜见报道。光照减少改变土壤温、湿度的同时是否会影响微生物数量和群落组成？若微生物发生改变是否会影响土壤养分循环和根系吸收养分的过程？活力低的根系是否会产生某种分泌物加强与有益微生物的互作, 从而增加对养分的吸收能力？这些问题需要进一步探索和研究。

二是弱光胁迫降低玉米产量的问题仍亟待解决。目前仍缺少系统评估耐阴品种的指标和精确的育种策略。未来需要将生化手段(转录组学、蛋白质组学、代谢组学等)和遗传策略(转基因技术、QTL定位等)结合, 找到耐阴性状的主导调控基因, 为培育耐阴型新品种提供理论依据。未来需要开展耐阴品种的筛选和培育、抗逆高产栽培技术的攻关等工作。如何构建植株形态以最大限度地截获光能？如何调控叶片中的氮素分布以提高光合效率？如何最大化地发挥植物生长调节剂的调控作用？从品种和栽培措施两方面入手, 寻求缓解弱光胁迫降低玉米产量的途径, 为实现玉米抗逆、稳产、高效提供科学依据。

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Physiological mechanism and regulation effect of low light on maize yield formation

SUN Zhi-Chao and ZHANG Ji-Wang*

Agronomy College, Shandong Agricultural University / State Key Laboratory of Crop Biology, Tai’an 271018, Shandong, China

As for global climate change, insufficient light during the growth periods has become one of the main factors restricting maize yield, increasing the risk of global food production and nutritional security. In this study, based on the previous experiments, we explored the physiological mechanism of low light on maize yield formation from the aspects of photosynthetic performance, nutrient absorption characteristics, grain formation, and filling characteristics. Under low light stress, the light harvesting ability of leaves was reduced, the stromal and grana thylakoids disintegrated, the activities of related enzymes were reduced, the photosystem was damaged, and the carbon assimilation ability was reduced, which further inhibited root development, significantly affected root morphology and function, and was not conducive to nutrient absorption and metabolism. Due to the insufficient nutrition supply, the development of tassel and ear was blocked, the morphological function of pollen and filaments was affected, resulting in low flower fertilization rate and decreased grain number per ear. Low light also reduced the number of endosperm cells— “sink” capacity, the structure and function of the endosperm transfer cells were affected, the endogenous hormonal balance was broken, sucrose, starch metabolism related enzyme activity decreased, internodes vascular bundle number and area reduced, transport and transformation ability were limited, eventualy led to the poor state of starch and the decreased grain weight significantly. Therefore, to alleviate the influence of low light stress on maize yield formation, it is urgent to establish indexes for systematic evaluation of shade tolerance varieties, accelerate the cultivation of new shade-tolerant varieties with high light efficiency by modern technology, and adopt cultivation measures such as increasing nitrogen fertilizer application, removing top leaves, spraying growth regulator and foliar fertilizer to improve maize yield. In the future, more attention should focus on root-shoot coordination and deeply explore the mechanism of low light stress, so as to provide the theoretical basis for the establishment of key techniques of maize resistance to yield increase.

low-light stress; artificial shading; maize; yield; shade tolerance; physiological mechanism; regulation effect

10.3724/SP.J.1006.2023.13064

本研究由财政部和农业农村部国家现代农业产业技术体系建设专项(CARS-02-21), 山东省重点研发计划项目(2021LZGC014-2)和山东省中央引导地方科技发展资金项目(YDZX20203700002548)资助。

This study was supported by the China Agriculture Research System of MOF and MARA (CARS-02-21), the Shandong Province Key Research and Development Project (2021LZGC014-2), and the Shandong Central Guiding the Local Science and Technology Development (YDZX20203700002548).

通信作者(Corresponding author):张吉旺, E-mail: jwzhang@sdau.edu.cn

E-mail: 3148755134@qq.com

2021-11-15;

2022-08-01;

2022-08-11.

URL: https://kns.cnki.net/kcms/detail/11.1809.S.20220809.1536.005.html

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).