徐云姬^1,2,, 许阳东¹, 李银银¹, 钱希旸¹, 王志琴¹, 杨建昌^1,*,
1 扬州大学江苏省作物遗传生理重点实验室 / 粮食作物现代产业技术协同创新中心, 江苏扬州 225009
² 扬州大学教育部农业与农产品安全国际合作联合实验室, 江苏扬州 225009

Effect of Alternate Wetting and Drying Irrigation on Post-anthesis Remobilization of Assimilates and Grain Filling of Rice

XUYun-Ji^1,2,, XUYang-Dong¹, LIYin-Yin¹, QIANXi-Yang¹, WANGZhi-Qin¹, YANGJian-Chang^1,*,
1 Key Laboratory of Crop Genetics and Physiology of Jiangsu Province / Yangzhou University, Yangzhou 225009, Jiangsu, China
² Joint International Research Laboratory of Agriculture and Agri-product Safety, the Ministry of Education of China, Yangzhou University, Yangzhou 225009, Jiangsu, China
通讯作者:杨建昌, E-mail: jcyang@yzu.edu.cn, Tel: 0514-87979317
收稿日期:2018-09-4
接受日期:2018-01-8
网络出版日期:2018-01-26
版权声明:2018作物学报编辑部作物学报编辑部
基金资助:本研究由国家自然科学基金项目(31461143015, 31471438), 国家科技支撑计划项目(2014AA10A605), 国家重点研发计划(2016YFD0300206-4), 江苏高校优势学科建设工程项目(PAPD)和扬州大学高端人才支持计划项目(2015-1)资助
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摘要
为阐明干湿交替灌溉对水稻花后同化物转运和籽粒灌浆的影响及其生理原因, 大田种植扬两优6号、武运粳24和旱优8号3个水稻品种, 自移栽后10 d起, 设置常规灌溉(CI)、轻干-湿交替灌溉(WMD)和重干-湿交替灌溉(WSD) 3种灌溉模式, 观察产量及构成因素、强弱势粒灌浆动态、籽粒中酶活性变化、剑叶光合性能、茎鞘非结构性碳水化合物(NSC)运转及其淀粉水解酶活性变化, 并利用¹³C同位素示踪茎鞘物质运转动态。结果表明, 与CI相比, WMD显著增加了3个水稻品种的每穗粒数、千粒重和结实率, 进而提高籽粒产量。WMD显著提高千粒重和结实率的主要原因是促进了弱势粒的灌浆。WMD和WSD显著增强了茎鞘α-淀粉酶和β-淀粉酶活性, 促进同化物质再运转与分配, 提高茎鞘储藏物质对粒重的贡献率。其中WMD提高了剑叶光合性能以及增强了水稻弱势粒中蔗糖-淀粉代谢途径关键酶活性, WSD的作用相反。表明较好的叶片性能、花后茎中较多的同化物向籽粒转运、较高的茎鞘淀粉水解酶活性以及弱势粒中较高的糖代谢酶活性是WMD促进弱势粒灌浆的重要生理原因。

关键词：水稻;干湿交替灌溉;籽粒灌浆;¹³C同位素示踪;强势粒;弱势粒;茎鞘物质运转
Abstract
Alternate wetting and drying irrigation (AWD) has been widely adopted in rice production for saving water and increasing water use efficiency. However, there is limited information about how AWD affects post-anthesis remobilization of assimilates and grain filling. To elucidate this issue, we planted three rice cultivars, including Yangliangyou 6 (indica hybrid), Wuyunjing 24 (japonica) and Hanyou 8 (japonica) in the field. With treatments of conventional irrigation (CI), alternate wetting and moderate soil drying irrigation (WMD) and alternate wetting and severe soil drying irrigation (WSD) from 10 days after transplanting to maturity. Grain yield and its components, grain filling of superior and inferior spikelets, changes in activities of the key enzymes involved in the conversion from sucrose to starch in grains, photosynthetic traits of flag leaf, the remobilization of non-structural carbohydrates in stems (culms and sheaths) and changes in starch hydrolytic enzymes in stems were investigated and isotope ¹³C was applied to trace redistribution of stem reserves. WMD significantly increased number of spikelets per panicle, 1000-grain weight, percentage of filled grains and grain yield of all the tested cultivars as compared with CI. Increases in 1000-grain weight and percentage of filled grains under WMD were mainly due to the enhancement of grain filling in inferior spikelets. Both WMD and WSD significantly enhanced the activities of α-amylase and β-amylase in stems and promoted translocation and redistribution of stem reserves, and increased the contribution of reserved carbohydrates in stems to grain yield. Moreover, WMD strengthened photosynthetic efficiency of flag leaf and enhanced the activities of the key enzymes involved in the conversion from sucrose to starch in inferior spikelets, whereas WSD exhibited the opposite effects. The results suggest that better leaf performance and higher activities of starch hydrolytic enzymes in stems, more remobilization of assimilates from stems to grains, and stronger activities of the key enzymes involved in sugar metabolism in inferior spikelets under the WMD are important physiological reasons for the enhancement of grain-filling in inferior spikelets of rice.

Keywords：rice;alternate wetting and drying irrigation;grain filling;tracer of isotope ¹³C;superior spikelets;inferior spikelets;remobilization of reserves in stems

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徐云姬, 许阳东, 李银银, 钱希旸, 王志琴, 杨建昌. 干湿交替灌溉对水稻花后同化物转运和籽粒灌浆的影响[J]. 作物学报, 2018, 44(04): 554-568 https://doi.org/10.3724/SP.J.1006.2018.00554
XU Yun-Ji, XU Yang-Dong, LI Yin-Yin, QIAN Xi-Yang, WANG Zhi-Qin, YANG Jian-Chang. Effect of Alternate Wetting and Drying Irrigation on Post-anthesis Remobilization of Assimilates and Grain Filling of Rice[J]. Acta Agronomica Sinica, 2018, 44(04): 554-568 https://doi.org/10.3724/SP.J.1006.2018.00554
水稻籽粒充实的优劣和粒重的高低与颖花在穗上着生的位置密切相关。一般着生在稻穗中上部早开花的强势粒灌浆快、充实好、粒重高; 着生在稻穗下部迟开花的弱势粒灌浆慢、充实差、粒重低^[1,2]。通过遗传改良和栽培途径促进弱势粒灌浆是提高产量的重要途径, 也一直受到研究者们的关注^{[3,4,5,6,7,8]}。水稻干湿交替灌溉(AWD)作为一种新的节水灌溉技术已经在中国、孟加拉国、印度、越南等国被采用^[9,10,11,12]。该技术在水稻生育过程中保持土壤水层和自然落干相互交替, 可以显著减少灌溉用水, 提高灌溉水利用效率^[11,13-15]。有****提出, 与常规灌溉相比, AWD不仅可以保持甚至可以提高产量^[16,17,18]。但也有报道称, AWD会减少产量^[19,20]。目前, 关于AWD增加或减少产量的机制一直受到研究者们的关注^{[6,8,16,18-21]}。徐芬芬等^[21]观察到, 水稻土壤适度干旱后的复水可以增强灌浆前期籽粒的生理活性, 有利于灌浆和粒重提高。付景等^[18]报道, 结实期轻度干-湿交替灌溉可以显著提高水稻灌浆期剑叶的净光合速率和膜质过氧化酶活性, 增强根系氧化力和根系激素等根部性状以及根冠比, 进而提高结实率和粒重。陈婷婷等^[6,8]提出, 花后轻度干-湿交替灌溉和重度干-湿交替灌溉条件下, 水稻弱势粒中多种与灌浆相关的蛋白质表达或淀粉合成相关酶活性及其基因表达的差异是其灌浆速率和粒重增加或降低的重要原因。前人的研究大多集中于从水稻根系活力、叶片光合性能和籽粒内部活性3个方面阐述AWD对籽粒灌浆速率和粒重的影响机制, 有关干湿交替灌溉对花后茎(含鞘)中非结构性碳水化合物(NSC)的再运转与分配影响的研究较少。
水稻花前储存于茎鞘中的NSC既是籽粒灌浆物质的重要来源, 也是启动灌浆的重要物质基础^[22]。有研究报道, 水稻花前储存于茎鞘中的NSC对籽粒产量的贡献率可高达40%^[23,24,25]。但水稻AWD是否或如何促进茎鞘中NSC向籽粒转运, 进而促进弱势粒灌浆?相关研究较少。本研究以3个水稻品种为材料, 研究干湿交替灌溉对水稻产量及构成因素、强弱势粒灌浆动态、籽粒中酶活性变化、剑叶光合性能、茎鞘NSC运转及其淀粉水解酶活性变化, 并利用¹³C同位素示踪茎鞘物质运转动态, 以期从光合性能、茎鞘NSC转运、叶片标记¹³C运转、籽粒库活性等方面较为深入地揭示AWD对水稻花后同化物转运和籽粒灌浆的影响机制, 为水稻节水灌溉提供理论依据。

1 材料与方法

1.1 供试品种与试验处理

于2014—2015年在扬州大学江苏省作物遗传生理重点实验室试验农场进行试验。试验地前茬作物为小麦, 土壤为沙壤土, 耕作层含有机质2.02%、有效氮103.2 mg kg^-1、速效磷24.5 mg kg^-1、速效钾85.6 mg kg^-1。供试品种2014年为扬两优6号(两系籼型杂交稻)和武运粳24(常规粳稻), 2015年为旱优8号(粳型三系杂交稻)。每年5月10日至11日播种, 6月9日至10日移栽。株、行距为15 cm × 25 cm, 扬两优6号单本栽, 武运粳24和旱优8号双本栽。
自移栽后10 d, 设灌溉处理为: (1)常规灌溉(CI): 保持浅水层(1~2 cm), 收获前1周断水。(2)轻干-湿交替灌溉(WMD): 移栽10 d后, 自浅水层(1~2 cm)自然落干到土壤水势达-15 kPa时再灌水至浅水层, 如此循环。(3)重干-湿交替灌溉(WSD): 移栽10 d后, 自浅水层(1~2 cm)自然落干到土壤水势达-30 kPa时再灌水至浅水层, 如此循环。裂区设计, 灌溉方式为主区, 品种为裂区(小区), 两小区面积为8 m × 5 m, 重复3次, 随机区组排列。在试验大田建有砂浆混凝土为基底的遥控自动式遮雨大棚, 全钢架屋顶结构, 周边高3.6 m, 顶部高5.5 m, 薄膜的材质为聚碳酸酯型聚氨酯(PCU), 雨时关, 雨停即开, 在严格控水的基础上尽量避免遮光和增温现象。各试验小区内安装土壤水分张力计(中国科学院南京土壤研究所生产)监测土壤深度15~20 cm处水势。通过在灌溉管道上安装流量表(LXSG-50流量计, 上海水分仪表制造厂)记录灌水量。全生育期施纯氮240 kg hm^-2, 按基肥(移栽前1 d)∶分蘖肥(移栽后7 d)∶穗肥(叶龄余数2.0)=5∶2∶3施用。基施过磷酸钙(含P₂O₅ 13.5%) 445 kg hm^-2和氯化钾(含K₂O 62.5%)150 kg hm^-2。其余田间管理同当地常规高产栽培。

1.2 叶片水势测定

于水稻花后当WMD和WSD处理的土壤水势分别达到-15 kPa和-30 kPa时(即土壤落干期, 花后8 d和25 d, 分别用D1和D2表示)及其相应复水期(花后10 d和28 d, 分别用W1和W2表示), 采用压力室法(Model 3000, 土壤水分仪器公司, Santa Barbara, CA, USA)测定中午(11:30—12:30)水稻剑叶水势, 各处理重复测定10张叶片。

1.3 籽粒灌浆动态测定

于抽穗开花期选择穗型大小基本一致的穗子每小区200个并挂牌, 标记部分穗各颖花开花日期。自开花后6、12、18、24、30、36、45和50 d分别取各小区标记穗15个(籼稻扬两优6号取样到45 d)用于测定强、弱势粒增重动态。于土壤落干期(D1和D2)和复水期(W1和W2)分别取标记穗18个(各小区6个)剥取强、弱势粒, 置液氮冷冻10 min后放入-70℃冰箱保存用于蔗糖-淀粉代谢途径关键酶活性测定。强势粒为穗上第1、2天开花的颖花, 着生在穗顶部一次枝梗, 弱势粒为穗上最后2 d开花的颖花, 着生在穗基部二次枝梗。用于测定籽粒灌浆动态的籽粒在105℃杀青30 min后, 置于70℃烘箱中烘至恒重, 剥去颖壳后称重, 测定籽粒增重动态并参照朱庆森等^[26]方法用Richards方程^[27]对籽粒灌浆过程进行拟合, 计算灌浆速率。
W = A/(1 + Be^-kt)^1/N (1)
对方程(1)求导, 得到籽粒灌浆速率(G)。
G = AkBe^-kt/N(1 + Be^-kt)^(N+1)/N (2)
式中, W为籽粒重量, A为最大籽粒重, t为开花后的时间(d), B、k和N为方程参数。从籽粒最大粒重(A)的5%(t₁)到95%(t₂)定义为活跃灌浆期(D), D = 2(N+2)/K。活跃灌浆期内籽粒增加的重量除以活跃灌浆期为籽粒平均灌浆速率(G_mean)。

1.4 籽粒中蔗糖-淀粉代谢途径关键酶活性的测定

5~10粒去壳籽粒加3~5 mL 100 mmol L^-1 Tricine-NaOH提取液[pH 8.0, 含有10 mmol L^-1 MgCl₂, 2 mmol L^-1 EDTA, 50 mmol L^-1 2-mercaptoethanol, 12% (v/v) glycerol, 5% (w/v) PVP 40]于研钵中研磨(温度保持在0℃), 15 000 × g离心10 min (4℃), 上清液(粗酶液)用于各酶活性测定。参照Yang等^[28]方法测定蔗糖合酶(SuSase)、腺苷二磷酸葡萄糖焦磷酸化酶(AGPase)、淀粉合酶(StSase)和淀粉分支酶(SBE)的活性。

1.5 剑叶光合速率、超氧化物歧化酶(SOD)活性和丙二醛(MDA)含量测定

分别于上述土壤落干期(D1和D2)和复水期(W1和W2), 使用美国LI-COR-6400便携式光合测定仪(Li-Cor 6400 portable photosynthesis measurement system, Li-Cor, Lincoln, NE, USA)测定水稻植株剑叶的光合速率。测定时间为上午9:00—11:00, 使用红蓝光源, 光量子通量密度(PFD)为1200 μmol m^-2 s^-1, 叶室CO₂浓度为380 μmol mol^-1, 每个小区测定10张叶片。
分别于上述土壤落干期(D1和D2)和复水期(W1和W2), 取挂牌稻穗的剑叶于液氮冷冻10 min后放入-70℃冰箱保存待用。将冷藏的鲜样叶去除中部叶脉, 剪碎混匀后称取0.5 g, 加5 mL硫酸妥缓冲溶液(pH 7.8), 冰浴研磨至匀浆, 4℃离心20 min (12 000 r min^-1), 上清液即为酶提取液。采用NBT光化还原法^[29]测定SOD活性, 以抑制NBT光化还原50%的酶量为1个酶活力单位; 采用硫代巴比妥酸法^[30]测定MDA含量。为尽量减少叶片含水量差异的影响, 以干重计算SOD活性和MDA含量。

1.6 茎鞘非结构性碳水化合物(NSC)和淀粉水解酶(α-淀粉酶和β-淀粉酶)活性测定

自抽穗期至成熟期每隔10 d分别在各小区内选择生长整齐一致水稻植株5穴, 按叶、茎鞘和穗进行分解, 105℃下杀青30 min后, 70℃烘干后称重, 用蒽酮法^[31,32,33]测定茎鞘干样淀粉和可溶性总糖含量。NSC为淀粉和可溶性总糖的总和。
茎鞘NSC的运转率(%) = (抽穗期茎鞘NSC-成熟期茎鞘NSC)/抽穗期茎鞘NSC×100
茎鞘NSC对籽粒产量的贡献率(%) = (抽穗期茎鞘NSC-成熟期茎鞘NSC)/籽粒产量×100
分别于上述土壤落干期(D1和D2)和复水期(W1和W2), 取各处理植株茎鞘少许立即置液氮固定10 min后保存, 用以测定α-淀粉酶和β-淀粉酶活性。参照McCleary等^[34,35]的方法并稍作改进测定α-淀粉酶和β-淀粉酶。参照Bradford^[36]的考马斯亮蓝G-250染色法测定蛋白质含量, 以牛血清蛋白(BSA)作为标准样品。酶活性单位记为μmol mg^-1 protein h^-1。

1.7 剑叶¹³CO₂的饲喂和样品中¹³C的测定

于水稻孕穗期, 各小区分别选取长势一致的单茎30个挂牌标记, 将剑叶套上大小适中的聚乙烯薄膜塑料袋, 赶走空气后进行封闭, 并用医用注射器注入6 mL (粳稻, 叶片相对较小)或8 mL (籼稻, 叶片相对较大)的¹³CO₂气体(购自于上海化工研究院有限公司, 由上海稳定性同位素工程技术研究中心研发, ¹³CO₂的纯度 > 99%)。选取的每张叶片自然光照下光合同化30 min后立即缓慢移除塑料袋, 饲喂时间为天气晴朗的上午9:00—11:00。
于花后0、10、30和40 d, 选取各处理标记单株15个(各小区5个), 分根系(20 cm×20 cm×20 cm挖出整穴土块, 放入网袋冲洗干净, 挑出所选单茎对应的根系部分)、叶片、茎鞘和穗(籽粒), 105℃杀青30 min, 70℃烘干至恒重。粉碎混匀后过100目筛, 分别称取25.00 mg和3.00 mg过筛的样品, 分别利用CHNS元素分析仪(CHNS elemental analyzer, Vario marco cube, Elementar, Germany)和Isoprime公司的稳定同位素比例质谱仪(Isotope ratio mass spectrometer, Isoprime100, Elementar, Germany)测定总C含量和δ¹³C值, 计算同位素¹³C/¹²C比率(即R值)及¹³C含量。根据质谱仪使用手册, δ¹³C_样品(‰) = (R_样品/R_标准-1)×1000。稳定同位素比例质谱仪中的国际标准物质为美国南卡罗来纳州白垩纪皮狄组层位中的拟箭石化石(Pee Dee Belemnite, 即PDB, R_标准 = 0.0112372, 定义其δ¹³C_标准 = 0‰), 通过计算, 下文以百分数表示标记¹³C在植株体内的积累与分配情况。

1.8 考种计产

取成熟期各处理30穴植株, 考查每平方米穗数、每穗粒数、结实率和千粒重。实收各小区计产。

1.9 数据处理

采用Microsoft Excel 2003和SPSS 16.0统计软件分析试验数据, SigmaPlot 10.0作图。用最小显著差法(LSD_0.05)检验平均数。

2 结果与分析

2.1 土壤与叶片水势

在水稻灌浆期, WMD处理下土壤水势达到-15 kPa需要4~6 d, WSD处理下土壤水势需要10~12 d才能达到-30 kPa (图1)。在同一灌溉处理下, 3个供试水稻品种的土壤水势变化基本一致(图1)。由图1可知, 花后8 d及25 d, WMD和WSD处理的土壤水势分别达到灌浆过程中两个不同程度干湿交替灌溉处理共同的土壤落干期-15 kPa和-30 kPa (D1和D2), 花后10 d和28 d为处理的复水期(W1和W2, 图1中箭头所示)。
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图1干湿交替灌溉处理下水稻灌浆期土壤水势的变化
WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉; D1和D2表示土壤落干期; 箭头指示复水期。
-->Fig. 1Changes in soil water potential under alternate wetting and drying irrigation (AWD) during grain filling of rice
WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying; D1 and D2 represent soil water potential at -15 kPa and -30 kPa, respectively, under WMD and WSD. Arrows indicate the re-watering period.
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图2为中午水稻剑叶的水势情况。在土壤落干期(D1和D2), WMD和WSD处理下剑叶水势分别为-0.62~ -0.82 MPa和-0.91~ -1.27 MPa, 均显著低于CI处理(-0.40~ -0.64 MPa), 其中WSD处理降低的幅度更大。土壤复水期(W1和W2), WMD和WSD处理下的剑叶水势与对照CI无显著差异(图2)。
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图2干湿交替灌溉对灌浆期剑叶水势的影响
CI: 常规灌溉; WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉。D1和D2表示土壤落干期; W1和W2表示复水期。
-->Fig. 2Effect of alternate wetting and drying irrigation on water potential of the flag leaf during grain filling of rice
CI: conventional irrigation; WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying. D1 and D2 represent soil water potential at -15 kPa and -30 kPa, respectively, under WMD and WSD. W1 and W2 indicate the re-watering period.
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2.2 产量、产量构成因素以及灌溉水利用效率

与CI相比, WMD显著提高了扬两优6号、武运粳24和旱优8号的产量, 增加幅度分别为10.68%、10.96%和7.75% (表1)。WSD显著降低了3个水稻品种的籽粒产量(表1)。从产量构成因素分析, WMD和WSD均显著降低了供试水稻品种的每公顷穗数, 其中WSD处理后的穗数下降幅度较大。WMD却显著提高了每穗粒数、千粒重及结实率, WSD处理的结果则相反(表1)。
Table 1
表1
表1干湿交替灌溉对供试水稻产量及其构成因素的影响
Table 1Effect of alternate wetting and drying irrigation on grain yield and its components of rice

品种 Cultivar	灌溉 方式 Irrigation regime	产量 Grain yield (t hm-2)	穗数 Panicles (×104 hm-2)	每穗粒数 Number of spikelets per panicle	千粒重 1000-grain weight (g)	结实率 Filled grains (%)	整个生长期 灌溉水量 Irrigation water during the whole growing season (mm)	抽穗后 灌溉水量 Irrigation water after heading (mm)	灌溉水 利用效率 Water use efficiency for irrigation (kg grain m-3)
扬两优6号	CI	9.83 b	218.88 a	189.50 b	28.40 b	83.42 b	922 a	286 a	1.07 c
Yangliangyou 6	WMD	10.88 a	205.83 b	206.04 a	29.96 a	85.63 a	704 b	140 b	1.55 a
	WSD	7.22 c	186.69 c	177.40 c	26.88 c	81.06 c	516 c	108 c	1.40 b
武运粳24	CI	8.76 b	230.25 a	175.13 b	26.06 b	83.35 b	914 a	275 a	0.96 c
Wuyunjing 24	WMD	9.72 a	210.17 b	188.68 a	27.96 a	87.68 a	722 b	124 b	1.35 a
	WSD	5.99 c	189.18 c	160.30 c	24.36 c	81.12 c	536 c	104 c	1.12 b
旱优8号	CI	9.03 b	236.01 a	172.84 b	25.20 b	87.84 b	908 a	279 a	0.99 c
Hanyou 8	WMD	9.73 a	220.47 b	183.71 a	26.85 a	89.45 a	687 b	133 b	1.42 a
	WSD	6.97 c	208.85 c	162.42 c	24.16 c	85.02 c	528 c	94 c	1.32 b

同一品种不同字母表示在P = 0.05水平上差异显著。CI: 常规灌溉; WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉。Values within the same cultivar followed by different letters are significantly different at P < 0.05. CI: conventional irrigation; WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying.
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较CI处理而言, WMD和WSD均显著减少了3个供试水稻品种的灌溉用水量, 降低幅度分别为21.01%~24.34%和41.36%~44.03%, 抽穗后灌溉用水量也显著降低(表1)。另外, 干湿交替灌溉(AWD)显著提高了灌溉水利用效率(籽粒产量/整个生长期灌溉水量), 其中WMD处理下灌溉水利用效率达最高(表1)。表明WMD可提高灌溉水利用效率又可增加籽粒产量。

2.3 籽粒灌浆特性

由图3和表2可知, 3个供试水稻品种强势粒的粒重、最大灌浆速率和平均灌浆速率均显著高于弱势粒。与CI相比, WMD显著增加了供试水稻品种弱势粒的粒重、最大灌浆速率和平均灌浆速率, 对强势粒没有显著影响; WSD显著降低了强势粒和弱势粒的粒重、最大灌浆速率和平均灌浆速率。说明WMD主要是通过促进弱势粒灌浆来提高千粒重和结实率。
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图3干湿交替灌溉对供试水稻品种强、弱势粒增重动态和籽粒灌浆速率的影响
CI: 常规灌溉; WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉; S: 强势粒; I: 弱势粒。
-->Fig. 3Effect of alternate wetting and drying irrigation on grain weight and grain filling rate for superior and inferior spikelets of rice
CI: conventional irrigation; WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying; S: superior spikelets; I: inferior spikelets.
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Table 2
表2
表2干湿交替灌溉对水稻强、弱势粒灌浆特征参数的影响
Table 2Effect of alternate wetting and drying irrigation on grain filling parameters of superior and inferior spikelets of rice

品种 Cultivar	灌溉方式 Irrigation regime	粒位 Grain position	粒重 Grain weight (A) (mg grain-1)	最大灌浆速率 The maximum grain-filling rate (Gmax) (mg grain-1 d-1)	平均灌浆速率 The mean grain-filling rate (Gmean) (mg grain-1 d-1)
扬两优6号	CI	S	27.34 a	1.87 a	1.19 a
Yangliangyou 6		I	19.06 d	1.27 d	0.84 d
	WMD	S	27.64 a	1.89 a	1.21 a
		I	21.60 c	1.32 c	0.95 c
	WSD	S	24.82 b	1.61 b	1.03 b
		I	15.00 e	1.01 e	0.67 e
武运粳24	CI	S	26.84 a	1.89 a	1.22 a
Wuyunjing 24		I	16.91 d	1.16 d	0.77 d
	WMD	S	26.99 a	1.84 a	1.18 a
		I	18.80 c	1.32 c	0.88 c
	WSD	S	24.33 b	1.69 b	1.09 b
		I	15.00 e	1.01 e	0.67 e
旱优8号	CI	S	26.85 a	1.88 a	1.13 a
Hanyou 8		I	16.78 d	1.21 d	0.81 d
	WMD	S	26.92 a	1.86 a	1.16 a
		I	18.56 c	1.33 c	0.92 c
	WSD	S	24.67 b	1.63 b	1.08 b
		I	15.19 e	1.00 e	0.70 e

同一品种不同字母表示在P=0.05水平上差异显著。CI: 常规灌溉; WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉。S: 强势粒; I: 弱势粒。Values within the same cultivar followed by different letters are significantly different at P<0.05. CI: conventional irrigation; WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying. S: superior spikelets; I: inferior spikelets.
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2.4 籽粒中蔗糖-淀粉代谢途径关键酶活性变化

由图4可知, 3个供试水稻品种籽粒中的蔗糖合酶(SuSase, 图4-a~c)、腺苷二磷酸葡萄糖焦磷酸化酶(AGPase, 图4-d~f)、淀粉合酶(StSase, 图4-g~i)和淀粉分支酶(SBE, 图4-j~l)活性在灌浆前期表现为强势粒的显著高于弱势粒, 灌浆中后期逐渐呈现相反的趋势。在花后土壤落干期(D1和D2), 与CI相比, WMD处理下籽粒中上述4种蔗糖-淀粉代谢途径关键酶活性无明显变化; 在复水期(W1和W2), WMD处理显著提高了弱势粒中上述4种关键酶活性, 对强势粒无影响。不论土壤落干期还是复水期, WSD处理均显著降低了强势粒和弱势粒中上述酶活性(图4)。说明WMD增强上述4种关键酶活性是提高3个供试水稻品种弱势粒灌浆速率的主要原因之一。
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图4干湿交替灌溉对水稻籽粒中蔗糖合酶(SuSase, a~c)、腺苷二磷酸葡萄糖焦磷酸化酶(AGPase, d~f)、淀粉合酶(StSase, g~i)和淀粉分支酶(SBE, j~l)活性的影响
CI: 常规灌溉; WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉。S: 强势粒; I: 弱势粒。D1和D2表示土壤落干期。W1和W2表示复水期。
-->Fig. 4Effect of alternate wetting and drying irrigation on activities of sucrose synthase (SuSase), adenosine diphosphate glucose pyrophosphorylase (AGPase), starch synthase (StSase), and starch branching enzyme (SBE) in rice grains
CI: conventional irrigation; WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying. S: superior spikelets; I: inferior spikelets. D1 and D2 represent soil water potential at -15 kPa and -30 kPa, respectively, under WMD and WSD. W1 and W2 indicate the re-watering period.
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2.5 剑叶光合特性和茎鞘NSC的积累与运转

在土壤落干期(D1和D2), WMD处理的剑叶光合速率与对照CI无显著差异, WSD处理下剑叶光合速率降低显著(表3)。土壤复水后(W1和W2), 较CI处理而言, WMD处理显著提高了剑叶的光合速率, WSD处理下光合速率仍然最低(表3)。在土壤落干期, WMD处理下的剑叶SOD活性和MDA含量与对照CI无显著差异; 复水则显著增加了剑叶SOD活性和降低了MDA含量(图5)。无论是土壤落干期还是复水期, WSD处理均显著降低了剑叶SOD活性, 增加了MDA含量(图5)。3个供试水稻品种的变化趋势相同(表3和图5)。表明WMD处理可以延缓叶片衰老, 进而提高灌浆期剑叶的光合速率。
Table 3
表3
表3干湿交替灌溉对水稻剑叶光合速率的影响
Table 3Effect of alternate wetting and drying irrigation on photosynthetic rate of flag leaf of rice

品种 Cultivar	灌溉方式 Irrigation regime	光合速率 Photosynthetic rate (μmol m-2 s-1)
		D1	W1	D2	W2
扬两优6号	CI	20.59 a	21.13 b	15.89 a	15.96 b
Yangliangyou 6	WMD	21.00 a	24.08 a	16.20 a	17.81 a
	WSD	18.42 b	19.43 c	13.37 b	14.16 c
武运粳24	CI	20.61 a	20.30 b	16.23 a	16.56 b
Wuyunjing 24	WMD	20.75 a	23.05 a	16.56 a	18.03 a
	WSD	19.02 b	18.72 c	14.03 b	14.81 c
旱优8号	CI	21.38 a	20.43 b	15.92 a	15.38 b
Hanyou 8	WMD	20.83 a	22.94 a	16.11 a	17.09 a
	WSD	18.72 b	18.22 c	14.63 b	12.27 c

同一品种不同字母表示在P = 0.05水平上差异显著。CI: 常规灌溉; WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉。D1和D2表示土壤落干期; W1和W2表示复水期。Values within the same cultivar followed by different letters are significantly different at P < 0.05. CI: conventional irrigation; WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying. D1 and D2 represent soil water potential at -15 kPa and -30 kPa, respectively, under WMD and WSD. W1 and W2 indicate the re-watering period.
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图5干湿交替灌溉对供试水稻品种剑叶超氧化物歧化酶(SOD)活性和丙二醛(MDA)含量的影响
CI: 常规灌溉; WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉。D1和D2表示土壤落干期, W1和W2表示复水期。
-->Fig. 5Effect of alternate wetting and drying irrigation on SOD activity and MDA content of flag leaf of rice
CI: conventional irrigation; WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying. D1 and D2 represent soil water potential at -15 kPa and -30 kPa, respectively, under WMD and WSD. W1 and W2 indicate the re-watering period.
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与CI相比, WMD和WSD均显著降低了抽穗期和成熟期的茎鞘NSC积累量, 其中WSD降低的幅度远大于WMD (表4)。抽穗至成熟期茎鞘NSC运转量在不同灌溉处理间表现为WMD>WSD>CI, 运转率则表现为WMD和WSD处理下的差异不显著, 但均显著高于CI (表4)。经计算, 茎鞘NSC对籽粒产量的贡献率表现为WSD>WMD>CI。3个水稻品种的趋势相同。表明干湿交替灌溉(AWD)能够促进花前茎鞘临时性贮藏同化物质向籽粒运转并且显著增加茎鞘NSC对籽粒产量的贡献率。
Table 4
表4
表4干湿交替灌溉对供试水稻品种茎鞘NSC积累和运转的影响
Table 4Effect of alternate wetting and drying irrigation on NSC accumulation and remobilization of rice

品种 Cultivar	灌溉方式 Irrigation regime	茎鞘NSC积累 NSC accumulation in stems (g m-2)			NSC运转率 NSC remobilization (%)	NSC对籽粒产量 的贡献率 Contribution of NSC to grain yield (%)
		抽穗期 Heading	成熟期 Maturity	抽穗-成熟 Heading-maturity
扬两优6号	CI	282.89 a	214.05 a	68.84 c	24.33 b	7.00 c
Yangliangyou 6	WMD	275.06 b	170.45 b	104.61 a	38.03 a	9.61 b
	WSD	238.15 c	147.12 c	91.03 b	38.22 a	12.60 a
武运粳24	CI	248.12 a	192.58 a	55.54 b	22.38 b	6.34 c
Wuyunjing 24	WMD	236.84 b	152.54 b	84.30 a	35.59 a	8.67 b
	WSD	224.85 c	144.26 c	80.59 a	35.84 a	13.45 a
旱优8号	CI	256.00 a	198.13 a	57.87 c	22.61 b	6.41 c
Hanyou 8	WMD	241.88 b	156.02 b	85.86 a	35.50 a	8.83 b
	WSD	220.59 c	140.58 c	80.01 b	36.27 a	11.48 a

同一品种不同字母表示在P=0.05水平上差异显著。CI: 常规灌溉; WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉。Values within the same cultivar followed by different letters are significantly different at P<0.05. CI: conventional irrigation; WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying.
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2.6 茎鞘中淀粉含量及其水解酶活性变化

由表4和图6可知, 3个供试水稻品种抽穗开花期茎鞘贮藏的淀粉含量约占茎鞘NSC含量的75%~ 90%。在灌浆结实期, 茎鞘中淀粉的含量逐渐降低, 而且降低幅度随着干旱程度的加剧而增大, 降低幅度具体表现为WSD>WMD>CI (图6), 这与茎鞘NSC运转的变化趋势一致(表4), 表明灌浆期茎鞘NSC主要是淀粉经水解后向籽粒转运, 而且干湿交替灌溉(AWD)能够显著促进茎鞘淀粉的水解以及转运。
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图6水稻花后茎鞘中淀粉含量变化
CI: 常规灌溉; WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉。
-->Fig. 6Changes in starch content in rice stems
CI: conventional irrigation; WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying.
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α-淀粉酶和β-淀粉酶是淀粉水解的两个关键酶。在土壤落干期(D1和D2), 与CI相比, WMD和WSD均显著增强了茎鞘α-淀粉酶(图7-a~c)和β-淀粉酶(图7-d~f)活性, 其中WSD处理增加的幅度更大。土壤复水后(W1和W2), WMD处理下的上述2种淀粉水解酶活性略有提高, 但与CI处理无显著差异, 而WSD处理下茎鞘仍具有较高的α-淀粉酶和β-淀粉酶活性(图7)。表明茎鞘淀粉水解酶活性的提高是其淀粉转运加快的主要原因。从图7还可以看出, 干湿交替灌溉(AWD)处理下, α-淀粉酶活性远远高于β-淀粉酶, 而且前者提高幅度大于后者。表明茎鞘NSC或淀粉转运过程中, α-淀粉酶发挥的作用可能更大一些。
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图7水稻花后茎鞘中淀粉水解酶活性变化
CI: 常规灌溉; WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉。D1和D2表示土壤落干期, W1和W2表示复水期。
-->Fig. 7Changes in hydrolytic enzymes in rice stems
CI: conventional irrigation; WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying. D1 and D2 represent soil water potential at -15 kPa and -30 kPa, respectively, under WMD and WSD. W1 and W2 indicate the re-watering period.
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图8显示, 开花时标记剑叶¹³C的72.88%~ 84.00%分配到茎鞘中(图8-a~c), 少部分(15.67%~ 19.22%)滞留在叶片中(表5), 极微量的分配到穗子中(数据未显示), 根系中未检测到¹³C, 表明开花前植株茎鞘是光合同化物质的临时性贮藏库。随着灌浆的进行, 叶片中滞留的¹³C逐渐减少, 到花后30 d已降低到标记¹³C的1.97%~6.05% (表5)。无论哪种灌溉处理下, 茎鞘中¹³C比例均呈现降低趋势(图8-a~c), 而籽粒中¹³C则逐渐积累(图8-d~f)。灌浆期间茎鞘中¹³C比例均表现为CI>WMD>WSD, 籽粒中¹³C比例则呈现CI<WMD<WSD (图8)。3个供试水稻品种的结果一致。花后40 d, 在WMD和WSD处理下, 通过剑叶光合同化饲喂的¹³C在水稻茎鞘中比例已降为8.40%~15.84% (图8-a~c), 在籽粒中已积累到70.50%~84.20% (图8-d~f)。再次表明干湿交替灌溉(AWD)促进了花前茎鞘贮藏同化物向籽粒的再转运, 而且干旱程度越大, 这种促进作用就越大。
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图8水稻灌浆期茎鞘和籽粒中¹³C分配的变化
CI: 常规灌溉; WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉。
-->Fig. 8Changes in ¹³C-distribution in rice stems and grains during grain filling
CI: conventional irrigation; WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying.
-->

Table 5
表5
表5水稻灌浆期叶片中¹³C的分配比例
Table 5Proportion of ¹³C-distribution in rice leaves during grain filling

品种 Cultivar	灌溉方式 Irrigation regime	叶片中13C分配比例 13C-distribution in rice leaves (%)
		抽穗期 Heading	花后10 d 10 DPA	花后30 d 30 DPA
扬两优6号	CI	15.67 a	11.88 a	4.62 a
Yangliangyou 6	WMD	16.20 a	9.74 b	3.04 b
	WSD	16.89 a	7.00 c	1.97 c
武运粳24	CI	18.25 a	12.39 a	5.12 a
Wuyunjing 24	WMD	17.88 a	11.86 a	2.38 b
	WSD	18.43 a	6.87 b	2.00 b
旱优8号	CI	19.03 a	14.21 a	6.05 a
Hanyou 8	WMD	18.41 a	13.69 ab	4.97 b
	WSD	19.22 a	12.43 b	4.33 b

同一品种不同字母表示在P=0.05水平上差异显著。CI: 常规灌溉; WMD: 轻干-湿交替灌溉; WSD: 重干-湿交替灌溉; DPA: 花后天数。Values within the same cultivar followed by different letters are significantly different at P<0.05. CI: conventional irrigation; WMD: alternate wetting and moderate soil drying; WSD: alternate wetting and severe soil drying; DPA: days post-anthesis.
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2.7 籽粒中蔗糖-淀粉代谢途径关键酶活性、剑叶性能以及茎鞘中淀粉水解酶活性与籽粒灌浆及物质运转的相关

由表6可见, 籽粒粒重、最大灌浆速率和平均灌浆速率与SuSase、AGPase和StSase活性以及剑叶光合速率、超氧化物歧化酶活性均呈极显著正相关(r = 0.55^**~0.94^**, P=0.01), 与剑叶丙二醛含量呈极显著负相关(r = -0.82^**~ -0.90^**, P=0.01), 与SBE活性相关性不显著(r = 0.35~0.43, P>0.05)。表明增加灌浆期籽粒中SuSase、AGPase和StSase活性以及提高叶片光合性能, 有利于促进籽粒灌浆, 进而增加粒重。
Table 6
表6
表6籽粒中蔗糖-淀粉代谢途径关键酶活性和剑叶光合性能与籽粒灌浆的相关系数
Table 6Correlation coefficients of key enzyme activities in sucrose-starch pathway and photosynthetic characteristics of flag leaf with grain weight and grain filling rate

项目 Item	粒重 Grain weight	最大灌浆速率 The maximum grain-filling rate (Gmax)	平均灌浆速率 The mean grain-filling rate (Gmean)
蔗糖合酶活性 SuSase activity	0.56**	0.55**	0.59**
腺苷二磷酸葡萄糖焦磷酸化酶活性 AGPase activity	0.59**	0.62**	0.65**
淀粉合酶活性 StSase activity	0.55**	0.58**	0.57**
淀粉分支酶活性 SBE activity	0.35	0.40	0.43
剑叶光合速率 Photosynthetic rate of flag leaf	0.82**	0.91**	0.89**
剑叶超氧化物歧化酶活性 SOD activity of flag leaf	0.87**	0.94**	0.93**
剑叶丙二醛含量 MDA content of flag leaf	-0.82**	-0.88**	-0.90**

^** 表示0.01水平上相关显著 (与蔗糖-淀粉代谢途径关键酶活性的相关n=36; 与剑叶光合性能的相关n=27)。^** Significant at P=0.01 (n=36 for correlations with key enzyme activities in sucrose-starch pathway and n=27 for correlations with photosynthetic characteristics of flag leaf).
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表7表明, 茎鞘α-淀粉酶和β-淀粉酶活性与茎鞘NSC运转率、NSC对产量的贡献率、淀粉运转、¹³C运转以及籽粒中¹³C分配比例呈显著或极显著正相关(r = 0.67^*~0.94^**, P=0.01), 与茎鞘中¹³C滞留比例呈极显著负相关(r =-0.77^**~ -0.92^**, P=0.01)。再次表明, 较高的α-淀粉酶和β-淀粉酶活性是茎鞘贮藏物质再转运并分配至籽粒的重要生理原因, 提高茎鞘淀粉水解酶活性, 有利于促进茎鞘物质转运, 进而提高粒重。
Table 7
表7
表7茎鞘中淀粉水解酶活性与物质运转的相关系数
Table 7Correlation coefficients of starch hydrolytic enzymes activities in stems with carbon remobilization

与相关 Correlations with	茎鞘中α-淀粉酶活性 α-amylase activity in stems	茎鞘中β-淀粉酶活性 β-amylase activity in stems
茎鞘中NSC运转 NSC remobilization	0.90**	0.67*
茎鞘中NSC对产量的贡献率 Contribution of NSC to grain yield	0.93**	0.80**
茎鞘中淀粉运转 Starch remobilization in stems	0.94**	0.79**
茎鞘中13C 13C in stems	-0.92**	-0.77**
茎鞘中13C运转 13C remobilization in grains	0.92**	0.79**
籽粒中13C 13C in grains	0.91**	0.84**

^*和^** 分别表示0.05和0.01水平上相关显著(n=27)。^*, ^** Significant at P = 0.05 and P =0.01, respectively (n=27).
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3 讨论

有关干湿交替灌溉对产量影响的报道, 有的增产^[16,17,18], 有的减产^[19,20], 其差异可能与土壤落干的程度、灌溉处理的时期以及水稻品种的抗旱性等有密切关系。本研究表明, 与常规灌溉(CI)相比, 3个供试水稻品种在全生育期轻干-湿交替灌溉(WMD)下可增产7.75%~10.96%, 在重干-湿交替灌溉(WSD)下则减产22.81%~31.62%。表明干湿交替灌溉中土壤落干程度是决定产量增减的重要原因, WMD不仅可提高灌溉水利用效率, 而且可增加籽粒产量。WSD虽可提高灌溉水利用效率, 但会严重减产。从产量构成因素分析, WMD处理显著增加了各品种的每穗粒数、千粒重和结实率, 而WSD的作用则相反。本研究还发现, WMD可显著增加稻穗弱势粒的粒重、最大灌浆速率和平均灌浆速率, 对强势粒则无显著影响。表明WMD促进弱势粒灌浆是千粒重和结实率提高的主要原因。
陈婷婷等^[6,8]报道, 结实期轻干-湿交替灌溉能够显著提高弱势粒中多种与灌浆相关的蛋白质表达或淀粉合成相关酶活性及其相关基因的表达, 进而增加弱势粒粒重。本研究观察到, WMD可显著提高灌浆期剑叶中超氧化物歧化酶(SOD)活性, 降低过氧化物(MDA)含量, 提高剑叶的光合速率, WSD处理的结果与之相反。粒重和籽粒灌浆速率与剑叶光合速率、SOD活性均呈极显著正相关, 与剑叶MDA含量呈极显著负相关。表明WMD可以增强叶片光合能力, 加大光合产物对籽粒特别是弱势粒的供给量。从籽粒内部因素分析, WMD显著增强了弱势粒中蔗糖合酶(SuSase)、腺苷二磷酸葡萄糖焦磷酸化酶(AGPase)、淀粉合酶(StSase)和淀粉分支酶(SBE)活性, WSD则显著降低了籽粒中上述4种关键酶活性。说明灌浆期弱势粒生理活性的增强, 是WMD促进弱势粒灌浆和增加粒重的重要生理原因。
水稻抽穗前茎鞘中储存的碳水化合物是灌浆物质的重要组成部分^[22,37-39]。有研究表明, 抽穗后土壤遭受干旱, 稻茎中储存的NSC会大量转运至籽粒, 对籽粒最终产量的贡献率可达40%以上^[38]。但干湿交替灌溉是否可促进茎中同化物向籽粒转运, 相关研究很少。本研究表明, 无论是WMD还是WSD, 均可显著增加茎鞘中NSC向籽粒的转运。WMD既可提高花后叶片光合速率, 又可促进茎中同化物向籽粒转运, 因此产量显著提高, 而在WSD条件下, 茎中光合同化物向籽粒转运增加之得不能补偿光合作用下降之失, 导致产量下降。
水稻干湿交替灌溉如何促进同化物向籽粒转运, 其机制仍不清楚。本研究发现, WMD和WSD可显著增强茎鞘中α-淀粉酶和β-淀粉酶活性。¹³C同位素示踪试验进一步显示, 随着籽粒的灌浆, 茎鞘中¹³C比例逐渐降低, 籽粒中¹³C比例逐渐增加。相关分析表明, 茎鞘α-淀粉酶和β-淀粉酶活性与茎鞘NSC运转率、NSC对产量的贡献率、淀粉运转率、¹³C运转率以及籽粒中¹³C分配比例均呈显著或极显著正相关, 与茎鞘中¹³C滞留比例呈极显著负相关。表明α-淀粉酶和β-淀粉酶活性的大幅度提高是AWD处理下茎鞘NSC向籽粒转运的重要生理原因。Morita等^[40]和杨建昌等^[25,41]也有类似的研究结果。本研究还观察到, 水稻茎鞘中α-淀粉酶活性在AWD条件下增加的幅度大于β-淀粉酶。α-淀粉酶活性与物质运转的相关系数均大于β-淀粉酶。据此作者推测, AWD对α-淀粉酶活性的增强作用较对β-淀粉酶的促进作用更大, 前者与茎中同化物转运的关系较后者更为密切。但这一推测需要进一步的验证。
值得注意的是, 本研究中WMD处理不仅提高了水稻的千粒重与结实率, 还提高了每穗粒数, WSD则显著降低了每穗粒数、千粒重和结实率。张慎凤^[42]也有相近的研究结果。每穗粒数多, 说明颖花分化数多或颖花退化数少, 或两者兼之。表明WMD有利于稻穗颖花发育与形成。但有关干湿交替灌溉影响水稻颖花分化和退化的机制, 作者尚未查到相关文献, 也缺乏研究探讨。深入开展这方面的研究, 对于揭示干湿交替灌溉影响水稻产量形成的机制, 指导优质高产节水灌溉有重要意义。

4 结论

水稻干湿交替灌溉可显著增强花后茎鞘中α-淀粉酶和β-淀粉酶活性, 促进茎中同化物向籽粒转运。轻干-湿交替灌溉(WMD)可增强灌浆期弱势粒中蔗糖-淀粉代谢途径相关酶活性, 促进弱势粒灌浆, 进而提高结实率和粒重, 重干-湿交替灌溉(WSD)则可抑制弱势粒灌浆。在WMD下, 灌浆期叶片光合速率的提高, 茎中同化物向籽粒转运的增加以及弱势粒活性的增强是产量和水分利用效率提高的重要生理基础; WSD虽能提高水分利用效率, 但因茎中光合同化物向籽粒转运增加之得不能补偿光合作用下降之失, 导致产量下降。WMD还可增加每穗粒数, 其机制有待深入研究。
The authors have declared that no competing interests exist.
作者已声明无竞争性利益关系。

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参考文献文献选项 原文顺序
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