吸收与分配规律的初步研究

选择苗期耐盐性较强的水稻(Oryza sativa)品种（株系）‘AB52’、‘02402’和‘02435’及敏感品种‘日本晴’, 在网室周转箱内,设置5 000和8 000 mg•L^－1 NaCl两种盐处理,以清水为对照, 研究盐胁迫下苗期水稻植株不同部位Na⁺和K⁺的吸收和分配与品种耐盐性的关系。结果表明,盐胁迫下,株高、绿叶干重和绿叶面积下降,绿叶中的水分含量降低,但茎鞘中的水分含量有所上升。5 000 mg•L^－1 NaCl胁迫处理10 d,耐盐品种所受的生长影响和叶片伤害程度低于敏感品种,但8 000 mg•L^－1 NaCl胁迫处理下品种间差异变小。盐胁迫下,水稻植株吸收 Na⁺和置换出K⁺,但不同器官部位中Na⁺和K⁺的区域化分布特征明显,各部位的Na⁺含量由低到高依次为绿叶、根、茎鞘和枯叶。下部老叶能优先积累较多Na⁺而枯黄;绿叶吸收Na⁺ 相对较少,维持较低的Na⁺水平,同时保持较高且稳定的K⁺含量;植株茎鞘通过选择性吸收大量Na⁺ 和置换出一部分K⁺到叶片中,保持绿叶较稳定的K⁺含量和相对较低的Na⁺含量,维持较高的K⁺ /Na⁺比,从而使植株少受盐害。敏感品种‘日本晴’在盐胁迫下绿叶中的Na⁺含量相对较高,且 5 000 mg●L^－1 NaCl胁迫下绿叶Na⁺含量已接近高值,与在8 000 mg●L^－1 NaCl胁迫下差异不大, 而耐盐品种绿叶吸收较少的Na⁺。另一方面,耐盐品种茎鞘的含K⁺相对较高,在盐胁迫下能吸收容纳较多的Na⁺,而绿叶中K⁺/Na⁺比较高。可以认为,绿叶的K⁺/Na⁺比可作为一个衡量耐盐性的相对指标。     

大气CO_2浓度倍增对油菜韧皮部汁液成分及根部氮素积累的影响

以甘蓝型欧洲油菜(Brassica napus)‘814’和‘湘油15’两个品种为研究对象,探寻在两个CO2浓度(自然CO2浓度:400μmol·mol–1和高CO2浓度:(800±20)μmol·mol–1)和两个氮素水平(低氮和常氮)处理下,欧洲油菜韧皮部汁液中可溶性糖和游离氨基酸含量,以及根部干物质量和氮素累积量的变化。结果表明:1)CO2浓度升高提高欧洲油菜韧皮部汁液可溶性糖含量,施氮条件下‘814’在抽薹期达到0.29%,‘湘油15’在盛花期达到0.25%,其含量均显著高于自然CO2浓度处理。2)CO2浓度对韧皮部汁液游离氨基酸含量的影响因品种而异,无论施氮与否,CO2浓度升高使‘814’的游离氨基含量降低;而‘湘油15’CO2浓度升高促使其在低氮条件下含量升高,在常氮条件下则降低。3)根部干物质量和氮素累积量均随CO2浓度升高而增加,且欧洲油菜韧皮部汁液中可溶性糖含量与游离氨基酸含量与根部干物质量和氮素累积量呈显著正相关。     

施氮对不同品种冬小麦氮素累积和运转的影响

在鄂北岗地以当地主栽的5个冬小麦品种‘鄂麦14'、‘鄂麦18'、‘鄂麦23'、‘郑麦9023'、和‘洛麦1号'为试验材料,通过田间裂区试验在不施氮(0 kg/hm2)和施氮(195 kg/hm2)条件下研究不同品种小麦氮素的累积、转移与分配规律的差异.结果表明:(1)在扬花期,不施氮处理叶片、茎鞘和穗部氮素累积量均为‘鄂麦14' 最大,积累量分别达到14.2 、16.6 和10.8 kg/hm2;施氮后‘鄂麦23' 的叶片氮素积累量最大(71.5 kg/hm2),‘鄂麦14' 的茎鞘积累量最大(69.0 kg/hm2),‘鄂麦18'的穗部积累量最大(34.2 kg/hm2).(2)成熟后不同部位氮素转移效率表现为叶片>穗>茎鞘,且叶、茎鞘、穗氮素转移效率存在品种差异;不同品种间氮肥效率差异显著,并以‘鄂麦23'的氮肥利用率、氮肥农学效率最高,而‘郑麦9023'的氮肥生理效率最高.(3)在氮胁迫条件下,扬花前‘鄂麦14'各器官氮素累积量、成熟期的氮素转移率及籽粒氮素累积量都显著高于其它品种;而在施氮条件下,冬小麦各器官氮素的累积、转移与分配因品种不同而异,‘鄂麦14'和‘鄂麦23'籽粒及植株氮素累积量都显著高于其它品种.研究发现,冬小麦氮素的累积、转移与分配受品种与氮素调控共同影响;施氮能显著提高各器官氮素的累积量,且提高的幅度因品种而异.     

红光与远红光比值对温室切花菊形态指标、叶面积及干物质分配的影响

以切花菊品种‘神马’(Chrysanthemum morifolium Ramat ‘Jinba’)为试材,于2010-2011年设计不同红光(R: (660 ±10) nm)与远红光(FR: (730±10)nm)比值(R/FR分别为0.5、2.5、4.5、6.5)的LED灯照射处理,研究不同R/FR值对温室切花菊形态指标、叶面积形成及干物质分配的影响。结果显示R/FR=2.5处理的植株叶片数、株高、茎粗、花径、叶面积及总干重均为各个处理中最高,R/FR=0.5处理的节间最长。所有R/FR处理的单株地上干物质重量与光质处理天数呈指数-线性模型。随处理天数的增加不同R/FR值处理菊花植株地上部分及地下部分干物质分配指数差异均不显著,叶片和花的干物质分配指数随处理天数的增加分别呈降低和升高的趋势,茎干物质分配指数则呈现先升高后降低的趋势,R/FR=2.5处理下,菊花叶片干物质分配指数和花干物质分配指数最高,而茎干物质分配指数却为最低;R/FR=6.5处理茎干物质分配指数最高,叶片干物质分配指数最低;0.5处理花朵干物质分配指数最低,说明远红光比例增加能够促进干物质向茎中分配,R/FR=2.5处理利于干物质向花朵中分配。     

大气CO2浓度倍增对油菜韧皮部汁液成分及根部氮素积累的影响

以甘蓝型欧洲油菜(Brassica napus) ‘814’和‘湘油15’两个品种为研究对象, 探寻在两个CO₂浓度(自然CO₂浓度: 400 μmol·mol^-1和高CO₂浓度: (800 ± 20) μmol·mol^-1)和两个氮素水平(低氮和常氮)处理下, 欧洲油菜韧皮部汁液中可溶性糖和游离氨基酸含量, 以及根部干物质量和氮素累积量的变化。结果表明: 1) CO₂浓度升高提高欧洲油菜韧皮部汁液可溶性糖含量, 施氮条件下‘814’在抽薹期达到0.29%, ‘湘油15’在盛花期达到0.25%, 其含量均显著高于自然CO₂浓度处理。2) CO₂浓度对韧皮部汁液游离氨基酸含量的影响因品种而异, 无论施氮与否, CO₂浓度升高使‘814’的游离氨基含量降低; 而‘湘油15’ CO₂浓度升高促使其在低氮条件下含量升高, 在常氮条件下则降低。3)根部干物质量和氮素累积量均随CO₂浓度升高而增加, 且欧洲油菜韧皮部汁液中可溶性糖含量与游离氨基酸含量与根部干物质量和氮素累积量呈显著正相关。     

江西千烟洲人工针叶林下狗脊蕨群落生物量

 根据野外调查和实验分析研究了江西省千烟洲人工针叶林下狗脊蕨（Woodwardia japonica）群落的生物量、细根生物量、净初级生产力(Net primary productivity, NPP)、 比叶面积（Specific leaf area, SLA） 和叶面积指数（Leaf area index, LAI）等。通过叶片参数和地上生 物量的相关关系建立了狗脊蕨单株地上生物量估算模型,分别 为W1=0.021H^1.545（R²=0.790）和W1=2.518（D²H）^{0 .616}（R²=0.894;H为株高 ,D为地径）。人工针叶林下灌草层地上生物量为367.8 g&;#8226;m^－2（52～932 g&;#8226;m^－2）,凋落物为1 631 g&;#8226;m^－2（672～2 763 g&;#8226;m^－2）,分别占 乔木层地上生物量的4.7%（1.55%～13.2%）和20.7%（7.6%～32.1%）。狗脊蕨群落地上生物量和NPP分别为266.6 g&;#8226;m^－2和88.67 g&;#8226;m^－2&;#8226;a ^-1 ,其中狗脊蕨种群占73.7%;地下生物量为212.6 g&;#8226;m^－2。狗脊蕨的SLA和叶干物质含量（Leaves day mutter content, LDMC）分别为144.0 cm²&;#8226;g^-1和31.99%,二者之间呈显著负相关;最佳叶面积估算模型为S=21.922 6-0.152L²+0.000 9L³（9.0≤L（叶片长度）≤23.5;1.4≤W （ 叶片宽度）≤5.9）。狗脊蕨种群的LAI为1.8。土壤含水量对狗脊蕨生物量有显著影响。群落生物量与土壤有机质和全氮含量正相关     

大气NH3浓度升高对不同氮效率玉米生理指标及生物量的影响

 该试验采用开顶式气室(Open top chambers)装置,在两种大气NH₃浓度水平(大气背景浓度值为10 nl&;#8226;L^－1和高NH₃浓度1 000 nl&;#8226;L^－1)和两种 供氮介质水平(高供氮介质和低供氮介质)下,对两种氮效率玉米(Zea mays)基因型(‘氮高效5号’(NE5)和‘氮低效四单19’(SD19))的叶绿素 指标值(SPAD值)、净光合速率(P_n)、气孔导度(G_s )、生物量和根冠比等生物学和生理学指标进行了测定。结果表明,大气NH₃浓度升高对两种 氮效率玉米基因型各生理指标有显著影响(p<0.05)。与大气背景NH₃浓度相比,当大气NH₃浓度为1 000 nl&;#8226;L^－1 时,生长在高供氮介质中‘氮 高效5号’的SPAD值、P_n和G_s分别降低7.0%、14.0%和6.5%,而‘氮低效四单19’的对应指标分别降低9.0%、11.0%和6.9%;生长在低供氮介质 中的两种氮效率玉米基因型各生理指标均显著增加(p<0.05)：‘氮高效5号’的SPAD值、P_n和G_s分别增加5.7%、7.1%和17%,‘氮低效四单19’ 的对应指标分别增加7.0%、11.0%和22.0%。高供氮介质中NH₃浓度升高对氮低效基因型玉米冠层生物 量抑制作用小于对氮高效基因型玉米的抑 制效应,而低供氮介质中NH₃浓度升高对氮高效基因型玉米冠部的促进作用显著高于对氮低效基因型玉米的促进作用(p<0.05);两种大气NH₃营 养下玉米根冠比的变化与采样时期有关。说明从大气中吸收NH3有利于改善生长在低供氮介质上玉米的氮素营养状况,而且对氮低效基因型玉米 的促进作用比对氮高效基因型玉米更加显著。     

DYNAMIC RESPONSE OF ROOT BORDER CELLS AND THEIR ASSOCIATED MUCILAGE EXUDATION IN SOYBEAN TO AI STRESS AND RECOVERY

 以耐铝性明显差异的两个大豆(Glycine max)基因型‘浙秋2号’(耐性)和‘浙春3号’(敏感)为材料, 研究根尖边缘细胞比活度、粘液分泌和根长对铝胁迫和解除胁迫的反应, 明确边缘细胞的粘液分泌对策在铝毒环境中的生态学意义。结果表明, ‘浙秋2号’在100~400 µmol&;#8226;L^–1 Al³⁺处理的3~12 h, 边缘细胞比活率呈递减趋势, 12 h后比活率又略有上升。‘浙春3号’在300和400 µmol&;#8226;L^–1 Al³⁺处理的变化与前者一致。两个大豆基因型的粘液层随着Al³⁺浓度增加和时间延长而增厚, 并于400 µmol&;#8226;L^–1 Al³⁺处理24 h时达到最大(>17 µm)。‘浙秋2号’在低浓度Al3+ (100和200 µmol&;#8226;L^–1)处理3~6 h后就会分泌大量粘液, ‘浙春3号’则在300 µmol&;#8226;L^–1 Al³⁺处理12 h后才有类似的变化。‘浙秋2号’在400 µmol&;#8226;L^–1 Al³⁺处理下的根相对伸长率均高于100~300 µmol&;#8226;L^–1 Al³⁺处理, ‘浙春3号’则表现为Al³⁺浓度越高, 根伸长受抑越明显。Al³⁺胁迫解除后, ‘浙秋2号’的粘液分泌速度和分泌量急剧下降, ‘浙春3号’在胁迫解除后的24 h, 仍会持续、大量地分泌粘液(>19 µm)。可见, 耐性大豆通过在铝胁迫初期快速、大量地分泌粘液以维持较高的边缘细胞活性和解除胁迫后迅速降低粘液的分泌速度及分泌量来适应铝毒害环境。     

浓度升高对不同氮效率玉米生理指标及生物量的影响

该试验采用开顶式气室(Open top chambers)装置,在两种大气NH₃浓度水平(大气背景浓度值为10 nl&#8226;L^－1和高NH₃浓度1 000 nl&#8226;L^－1)和两种 供氮介质水平(高供氮介质和低供氮介质)下,对两种氮效率玉米(Zea mays)基因型(‘氮高效5号’(NE5)和‘氮低效四单19’(SD19))的叶绿素 指标值(SPAD值)、净光合速率(P_n)、气孔导度(G_s )、生物量和根冠比等生物学和生理学指标进行了测定。结果表明,大气NH₃浓度升高对两种 氮效率玉米基因型各生理指标有显著影响(p<0.05)。与大气背景NH₃浓度相比,当大气NH₃浓度为1 000 nl&#8226;L^－1 时,生长在高供氮介质中‘氮 高效5号’的SPAD值、P_n和G_s分别降低7.0%、14.0%和6.5%,而‘氮低效四单19’的对应指标分别降低9.0%、11.0%和6.9%;生长在低供氮介质 中的两种氮效率玉米基因型各生理指标均显著增加(p<0.05)：‘氮高效5号’的SPAD值、P_n和G_s分别增加5.7%、7.1%和17%,‘氮低效四单19’ 的对应指标分别增加7.0%、11.0%和22.0%。高供氮介质中NH₃浓度升高对氮低效基因型玉米冠层生物 量抑制作用小于对氮高效基因型玉米的抑 制效应,而低供氮介质中NH₃浓度升高对氮高效基因型玉米冠部的促进作用显著高于对氮低效基因型玉米的促进作用(p<0.05);两种大气NH₃营 养下玉米根冠比的变化与采样时期有关。说明从大气中吸收NH3有利于改善生长在低供氮介质上玉米的氮素营养状况,而且对氮低效基因型玉米 的促进作用比对氮高效基因型玉米更加显著。     

不同冬小麦品种在3种质地土壤中氮代谢特征及利用效率分析

为明确不同土壤质地条件下不同品种冬小麦(Triticum aestivum)的氮代谢和利用特征, 筛选与土壤质地相适宜的高产和氮高效利用的优质小麦品种, 采用大田试验的方法, 在同一生态类型区砂土、壤土和黏土3种质地土壤上, 以当地生产上大面积应用的强筋小麦‘郑麦366’ (‘ZM366’)和中筋小麦‘矮抗58’ (‘AK58’)、‘周麦22’ (‘ZM22’)为材料, 系统地研究了土壤质地对不同冬小麦品种主要生育时期叶片氨同化关键酶谷氨酰胺合成酶(GS)活性、游离氨基酸含量、花前和花后不同器官氮素积累和分配、氮素再分配等氮代谢过程及产量、品质和氮素利用效率等的影响。结果表明: 在这3种土壤质地上, 不同品种冬小麦旗叶GS活性和游离氨基酸含量均呈倒“V”型变化特征。各品种小麦旗叶GS活性、游离氨基酸含量大小及达到最大值的时期不一样, 砂土条件下峰值早于壤土10天左右出现, 且在5月22日已检测不到GS活性和游离氨基酸含量。花前和花后小麦地上部及各器官氮积累量(NA)、氮再分配量(NR)、成熟期籽粒产量和氮素当季利用率(NUE)均以壤土上为最高。氮素转运率(NRE)、花前再分配氮素对籽粒氮素的贡献率(NRC)、氮素生理效率(NPE)、氮收获指数(NHI)以砂土上为最高。其中, 砂土上NRC达82.46%-95.84%, 是花后的7倍左右; 壤土和黏土条件下花后吸收的氮素在籽粒氮素的积累中占有较大的比例, 贡献率分别为36.6%和29.2%。同一土壤质地上3个品种比较, 在砂土上, GS活性、游离氨基酸含量、籽粒产量、蛋白质含量及NUE和NPE以‘郑麦366’最高, 而壤土上以‘矮抗58’最高, 黏土上则以‘周麦22’最高。因此, 在生产上应培育和选择与土壤质地相适应的小麦品种, 砂土地种植‘郑麦366’, 壤土条件下种植‘矮抗58’, 黏土条件下种植‘周麦22’, 可以在获得较高产量和品质的同时, 提高氮素利用效率。     

Combined Effects of Partial Defoliation and Nutrient Availability on Cloned Betula pendula Saplings: I CHANGES IN GROWTH, PARTITIONING AND NITROGEN UPTAKE

The combined effects of partial defoliation and nutrient availabilityon dry matter accumulation and partitioning, and on nitrogenuptake and partitioning, were studied in cloned Betula pendulaRoth saplings. The saplings were randomly assigned to differentnutrient levels (5, 1·5 and 0·5 mol Nm^–3)in aerated nutrient culture and to the following defoliationtreatments: (1) control (no damage), (2)damage of the developingmain stem leaves (half of the leaf lamina removed), and (3)removalof the developing main stem leaves (entire leaf lamina removed).Measured in terms of cumulative whole-plant dry weight (includingremoved leaf tissue), the birch saplings were unable to compensatefor the loss of the developing leaves (treatment 3) during the14 d study period. In response to leaf removal (treatment 3)the mean final percentage reduction in whole-plant dry weightwas actually greater than the initial mean percentage reductioncaused by the removal itself; the magnitude of the final reductionwas independent of nutrient availability. After removal of thedeveloping leaves, branch growth was favoured at the expenseof the growth of the rest of the shoot; the relative branchgrowth was most pronounced at the highest nutrient level. Atthe two highest nutrient levels the nitrogen uptake of the saplingswith the developing leaves removed was less than that of undamagedsaplings. We suggest, however, that the incapacity of the saplingsfor compensatory growth after removal of the developing leaveswas primarily due to the decreased total carbon gain of thesaplings rather than to the decreased nitrogen uptake rate. Key words: Partial defoliation, nutrient availability, birch sapling, dry matter, nitrogen     

定植期和定植密度对温室单头切花菊外观品质的影响

定植期和种植密度是影响切花菊外观品质的重要栽培措施.本文以单头切花菊‘神马’（Chrysanthemum morifolium cv. Shenma）为材料,研究定植期和密度对温室单头菊外观品质的影响.结果表明,在试验的定植期和密度范围内,随着定植期的延迟、密度的增加,单头菊株高增加,单株叶数、茎直径减小,单株鲜质量降低,花颈长度增加,花朵直径减小,但密度对株高的影响不大.在上海地区非加温温室单头切花菊生产中,以生产A级产品为目标的适宜定植期为8月中旬,适宜种植密度为64株·m^-2;以生产B级产品为目标的适宜定植期为8月中旬至9月初,适宜种植密度为72～80株·m^-2.本研究为建立基于光、温和密度的温室单头切花菊外观品质预测模型提供了参考.     

Is Partitioning of Dry Weight and Leaf Area Within Dactylis glomerata Affected by N and CO2Enrichment?

We examined changes in dry weight and leaf area within Dactylisglomerata L. plants using allometric analysis to determine whetherobserved patterns were truly affected by [CO₂] and N supplyor merely reflect ontogenetic drift. Plants were grown hydroponicallyat four concentrations of in controlled environment cabinets at ambient (360 µll^–1) or elevated (680 µl l^–1) atmospheric[CO₂]. Both CO₂and N enrichment stimulated net dry matter production.Allometric analyses revealed that [CO₂] did not affect partitioningof dry matter between shoot and root at high N supply. However,at low N supply there was a transient increase in dry matterpartitioning into the shoot at elevated compared to ambient[CO₂] during early stages of growth, which is inconsistent withpredictions based on optimal partitioning theory. In contrast,dry matter partitioning was affected by N supply throughoutontogeny, such that at low N supply dry matter was preferentiallyallocated to roots, which is in agreement with optimal partitioningtheory. Independent of N supply, atmospheric CO₂enrichment resultedin a reduction in leaf area ratio (LAR), solely due to a decreasein specific leaf area (SLA), when plants of the same age werecompared. However, [CO₂] did not affect allometric coefficientsrelating dry weight and leaf area, and effects of elevated [CO₂]on LAR and SLA were the result of an early, transient stimulationof whole plant and leaf dry weight, compared to leaf area production.We conclude that elevated [CO₂], in contrast to N supply, changesallocation patterns only transiently during early stages ofgrowth, if at all. Copyright 2000 Annals of Botany Company Allometric growth, carbon dioxide enrichment, Cocksfoot, Dactylis glomerata L., dry weight partitioning, leaf area ratio, nitrogen supply, shoot:root ratio, specific leaf area     

Nitrogen Uptake and Plant Growth II. An Empirical Model of Vegetative Growth and Partitioning

An empirical model of vegetative plant growth is presented.The model is based on experimental data on Polygonum cuspidatum,which showed (1) that the partitioning of dry matter and nitrogenamong organs was linearly related to the nitrogen concentrationof the whole plant and (2) that leaf thickness was negativelycorrelated with leaf nitrogen concentration. The model properlydescribes the behaviour of plants. Steady-state solutions ofthe model give the relative growth rate, specific leaf weight,and partitioning of dry matter and nitrogen among organs withthe net assimilation rate and the specific absorption rate asenvironmental variables. The effect of nitrogen removal on drymatter and nitrogen partitioning was examined as non-steady-statedynamic solutions of the model. The model predicted not onlyreduced leaf growth and enhanced root growth but also a fluxof nitrogen from the leaf to the root, which agreed with theexperimental results. Mathematical model, partitioning of dry matter and nitrogen, plant nitrogen, relative growth rate, shoot: root ratio, specific leaf weight     

Pre-flowering Growth and Development of the Inflorescences of Maize: II. ACCUMULATION AND PARTITIONING OF DRY MATTER AND NITROGEN BY INFLORESCENCES

The accumulation and partitioning of dry matter and nitrogenwere examined in the developing tassel and two uppermost earshoots of field-grown maize under varying levels of appliednitrogen and times of sowing. Accumulation of dry matter and nitrogen within an axillary branchalways favoured the ear over the husk and shank. Dry matterand nitrogen accumulated faster in the first ear than in thetassel or second ear and the partitioning between inflorescencesof dry matter and nitrogen was not affected by treatment. Therelative rate of growth, RGR(dry matter), of the first and secondear shoots increased by up to 42% at high levels of appliednitrogen and with early sowing. In contrast, the relative rateof accumulation of nitrogen (RNAR) was not sensitive to N supply,although it was reduced, on average, by 22% at the late timeof sowing. We conclude that accumulation, but not partitioning, of drymatter and nitrogen between developing inflorescences of maizeare altered by nitrogen application, time of sowing, and positionof the inflorescence on the stem. Key words: Maize, N-application, partitioning, inflorescence, sowing time     

Uptake and Partitioning of Nitrogen by Maize Infected withStriga hermonthica

The uptake and partitioning of nitrogen (N) by maize infectedwith the parasitic angiosperm,Striga hermonthicawas investigatedin sand culture in a glasshouse. The purpose was to determinethe effect ofStrigaon N uptake and partitioning in maize. Maizewas grown at 22, 66 and 133 mg N per plant and sampled fivetimes. There was no significantStrigaxN interaction in any measuredresponse. Leaf dry matter ofStriga-infected maize, averagedover all N treatments, was 92% that of uninfected maize at thefour-leaf stage but by the 18-leaf stage it had decreased to58%. Similarly, stem dry matter of infected maize which was91% that of uninfected maize at the four-leaf stage was only42% at the 18-leaf stage. Root dry matter was similar for infectedand uninfected maize. N concentration in the leaf, stem androot declined asymptotically from the first to the last samplingdate for both infected and uninfected maize. The asymptoticvalue of N concentration inStriga-infected maize was 16% greaterin the leaf, 55% in the stem, and 21% in the root than in uninfectedmaize. The concentration of N inStrigawas higher than in maizeat the 16- and 18-leaf stages. Uptake of N was similar for infectedand uninfected plants at the four–eight leaf stage butat the eight–12 leaf stage, N uptake by infected maizewas 52% that of uninfected maize. However, the proportion oftotal plant nitrogen partitioned to the root was greater (P<0.001)forStriga-infected maize. These results showed that the extentto whichS. hermonthicareduced maize growth and N uptake, butincreased the proportion of N partitioned to the roots, didnot depend on the rate of N fertilizer applied.Copyright 1998Annals of Botany Company Maize; nitrogen; partitioning;Striga hermonthica; uptake.     

Dry Weight and N Partitioning in Relation to Substrate N Supply, Internal N Status and Developmental Stage in Jack Pine (Pinus banksianaLamb.) Seedlings: Implications for Modelling

Dry weight and nitrogen (N) partitioning of sand-cultured youngjack pine (Pinus banksianaLamb.) seedlings under controlledenvironments were studied 3, 6, 9, 12 and/or 15 weeks afterthe initiation of six dynamic N supply treatments. The supplyof other nutrients was maintained at optimal levels. Total dryweight varied widely among treatments and whole plant totalN concentration ranged from 10 to 32 mg g^-1d. wt at most samplingintervals. Whole plant N concentration changed, with time, accordingto three distinct patterns: (1) stable; (2) rapidly increasing;or (3) gradually declining. Regardless of N treatment and samplinginterval, whole plant N concentration was linearly and positivelycorrelated with root, needle and stem N concentration. Dry weightand N weight ratios of needles declined, whereas those of rootsincreased linearly with decreasing whole plant N concentration(r²=0.43 to 0.76) regardless of N regime. Dry matter partitioningto stems, however, was better explained by developmental stagethan by whole plant N concentration. With the decline in internalN status, N was increasingly concentrated in roots at the expenseof needles and stems. These results suggest: (1) dry weightand N partioning may be largely a function of the internal Nstatus of plant rather than root and shoot activities; (2) bothshoot and root specific activities may have a close, positiveassociation with whole plant N concentration; (3) N-partitioningmay be an active process itself and may warrant separate considerationfrom dry weight; and (4) developmental stage may be a significantdeterminant of partitioning, particularly to stems.Copyright1998 Annals of Botany Company Developmental stage; dry weight; internal N status; jack pine; modelling; nitrogen; partitioning;Pinus banksiana; substrate N supply.     

Modelling Nitrogen Content and Distribution in Cauliflower (Brassica oleracea L.botrytis )

A model of nitrogen uptake and distribution is presented whichdescribes these processes in relation to the amount of availablesoil nitrate and the rate of plant growth. Nitrogen uptake iseither sink or source limited. Sink limitation is based on maximumN-concentrations of plant compartments. The N-uptake model iscombined with a photosynthesis model based on the productivity-nitrogenrelationship at the single-leaf level. The model is parameterizedusing cauliflower as an example crop. Applied to an independentdata set, the combined model was able to predict leaf, stemand inflorescence nitrogen concentrations with correlation coefficientsbetween predicted and simulated values of 0.89, 0.66 and 0.86,respectively. The influence of nitrogen supply and light intensityon leaf nitrate-N could also be predicted with good accuracy(r² = 0.87). Dry matter production based on the productivity-Nrelationship and the partitioning into leaf, stem and inflorescencewas also reproduced satisfactorily (r² = 0.91, 0.93 and 0.92,respectively). Copyright 2000 Annals of Botany Company Brassica oleracea L. botrytis, cauliflower, nitrogen, nitrate, nitrogen supply, nitrogen uptake, nitrogen distribution, model