硫膜和树脂膜控释尿素对小麦产量、品质及氮素利用率的影响

通过田间试验,研究了硫膜和树脂膜控释尿素对小麦产量、品质和耕层土壤无机氮含量及氮素利用率的影响.结果表明：与普通尿素相比,硫膜和树脂膜控释尿素均能显著提高小麦籽粒产量和品质,增产幅度达10.4%～16.5%,小麦籽粒蛋白质和淀粉含量分别提高5.8%～18.9%和0.3%～1.4%;两种控释肥均能有效保持耕层土壤无机氮含量,且其氮素后移的功效满足了小麦生育后期对氮素的需求;有效提高了氮肥偏生产力,降低了土壤氮素依存率（降幅11.0%～17.3%）,提高了氮素利用率（增幅58.2%～101.2%）.其中,树脂膜控释尿素比硫膜控释尿素表现出更好的增产效应,实现了氮素的高效利用.     

水稻土模拟土柱中肥料氮素的迁移转化特征

为了明确肥料氮素在模拟土柱中的迁移转化特征,通过布置室内模拟土柱试验,研究了3倍常规施肥水平下（360 mg·kg^-1）水稻土中矿质氮的变化.结果表明： 不同处理、不同土层间NH₄⁺-N和NO₃^--N含量差异显著.不施肥对照在整个培养期间养分含量变化不大,不同土层间亦没有显著性差异.施用尿素和硫铵后,土壤NH₄⁺-N和NO₃^--N含量显著提高,尤其是0～50 mm土层内,分别达到186.0～2882.1 mg·kg^-1和268.7～351.5 mg·kg^-1,分别相当于对照的4.8～242倍和5.7～316倍,50 mm以下各土层与对照处理相似,表明肥料氮素的迁移转化主要发生在0～50 mm土层内,并且在培养的前14 d变化最大.整个培养期间不同土层内,硫铵处理不同矿质态氮含量是尿素处理的0.7～2.0倍,硝化率是尿素处理的0.9～1.4倍,表明硫铵在水稻土中的转化效率略高于尿素.     

氮肥调控剂对潮褐土中不同氮源氮素转化及油菜生长的影响

采用土壤培养和盆栽试验相结合的方法,研究了硝化抑制剂双氰胺(DCD)与纳米碳配合施用对尿素和碳酸氢铵在华北平原典型土壤潮褐土中转化的调控效果及其对油菜生长的影响.结果表明： 尿素和碳酸氢铵在施入土壤后的2周内,土壤无机氮的供应强度差别较大,2周以后则基本相似.2种氮源对油菜生长及氮素利用的影响在生育前期(播种后34 d)差异显著,但最终达到商品生物量收获时,氮源之间差异不大.DCD对尿素和碳酸氢铵在潮褐土中的转化表现出显著的硝化抑制作用,其抑制强度和有效抑制时间随DCD用量的增加而增强,且以对碳酸氢铵施入土壤后的硝化抑制效果更好.在本研究条件下,DCD用量以占肥料纯氮量的1.0%～1.5%相对较佳,可显著提高油菜产量,改善叶色,降低植株硝酸盐含量,提高氮肥利用率.纳米碳与DCD配合施用对土壤铵氧化有明显的协同抑制效果,且可以显著刺激油菜前期的生长发育和氮素利用,降低油菜硝酸盐含量.     

深松与包膜尿素对玉米田土壤氮素转化及利用的影响

耕作方式和氮肥施用是影响土壤中氮肥转化、利用效率和作物产量的重要因素。通过夏玉米田的2a(2011—2012)定位试验,研究了两种耕作方式(深松、旋耕)配合不同尿素类型(包膜尿素、普通尿素)的施用对玉米田土壤硝态氮和铵态氮含量、脲酶活性、硝化细菌和反硝化细菌数量、玉米产量以及氮肥农学效率的影响。研究结果表明:相同耕作方式下,包膜尿素处理土壤中脲酶活性较稳定,且增加了旱田土壤亚硝酸细菌数量而降低了反硝化细菌数量,有利于土壤硝态氮含量的提高,尤其是作物生长的中后期;包膜尿素处理的产量比普通尿素提高7.25%—10.82%,同时提高氮肥农学效率。深松处理增加了土壤中的反硝化细菌数量,配合施用包膜尿素进一步提高了土壤脲酶活性,增加了亚硝酸细菌数量;旋耕与包膜尿素配合施用在一段时期内能显著增加土壤硝态氮含量,减少反硝化细菌数量。深松配合包膜尿素处理能够显著的增加玉米产量,2a分别比旋耕配合包膜尿素增加1.41%和10.62%。因此,深松措施配合施用包膜尿素能够增强土壤脲酶活性,增加亚硝酸细菌数量,提高氮素转化速率,增加作物产量和氮肥农学效率,其稳产效果在干旱年份尤为显著。     

速效氮肥配施双氰胺对减控小白菜镉积累的作用

本文以小白菜为试材,研究了镉(Cd)污染土壤中配施双氰胺(DCD)对不同速效氮肥(硫酸铵,简称全铵;硝酸钠,简称全硝;11硫酸铵和硝酸钠,简称硝铵;尿素)下小白菜生长及Cd含量的影响。结果表明: 与对照相比,Cd污染土壤中配施DCD使全铵、硝铵和尿素处理下的小白菜可食部分鲜重分别增加583.3%、41.5%和206.8%,耐受系数(TI)和光合作用速率均大幅度提高;全硝处理则无明显变化。配施DCD使各氮肥处理下小白菜叶片的丙二醛、过氧化氢含量和超氧自由基产生速率均不同程度地下降,且以全铵和尿素处理的下降幅度最大。与对照相比,全铵、硝铵和尿素处理的小白菜叶片的Cd含量分别减少58.3%、34.0%和44.5%;叶柄的Cd含量分别减少61.8%、29.4%和55.6%。全硝处理下小白菜叶片和叶柄的Cd含量与对照相比无明显差异。配施DCD不同程度降低了各处理根际土壤的酸化可能是造成上述结果的主要原因。在缓冲能力较弱的Cd污染土壤中,施用全铵、硝铵和尿素氮肥时配施DCD可以缓解Cd污染土壤对小白菜生长的胁迫,并有效减少Cd在植物体内的积累。     

南京郊区番茄地中氮肥的效应与去向

采用田间小区和微区试验,研究了施用化学氮肥对南京郊区菜地番茄产量、氮肥去向及氮素损失的影响.结果表明, 由于土壤和有机肥供氮充分,氮肥施用未增加番茄产量.用差值法计算得到的氮肥利用率在14.5%～22.5%之间.¹⁵N标记尿素微区试验表明,施入氮量的16.6%～28.8%被作物吸收,氮素总损失为34.2%～46.0%.施用化学氮肥增加了土壤剖面中的硝酸盐含量,番茄收获时,10%～10.2%的标记尿素被淋洗到40 cm以下土层.增施化学氮肥也显著增加了菜地土壤的反硝化损失和N₂O排放,其中反硝化损失占施入氮量的5.50%～6.01%;N₂O排放量占施入氮量的2.62%～4.92%.但番茄生长期间未检测到氨挥发.减少氮肥用量或施用包衣尿素可降低菜地施用氮肥的环境风险,特别是减少硝酸盐淋洗和硝化反硝化损失.     

氮肥调控剂对潮褐土中不同氮源氮素转化及油菜生长的影响

采用土壤培养和盆栽试验相结合的方法,研究了硝化抑制剂双氰胺(DCD)与纳米碳配合施用对尿素和碳酸氢铵在华北平原典型土壤潮褐土中转化的调控效果及其对油菜生长的影响.结果表明:尿素和碳酸氢铵在施入土壤后的2周内,土壤无机氮的供应强度差别较大,2周以后则基本相似.2种氮源对油菜生长及氮素利用的影响在生育前期(播种后34 d)差异显著,但最终达到商品生物量收获时,氮源之间差异不大.DCD对尿素和碳酸氢铵在潮褐土中的转化表现出显著的硝化抑制作用,其抑制强度和有效抑制时间随DCD用量的增加而增强,且以对碳酸氢铵施入土壤后的硝化抑制效果更好.在本研究条件下,DCD用量以占肥料纯氮量的1.0％ ～1.5％相对较佳,可显著提高油菜产量,改善叶色,降低植株硝酸盐含量,提高氮肥利用率.纳米碳与DCD配合施用对土壤铵氧化有明显的协同抑制效果,且可以显著刺激油菜前期的生长发育和氮素利用,降低油菜硝酸盐含量.     

施用纳米碳对烤烟氮素吸收和利用的影响

为明确纳米碳在提高烤烟氮素吸收利用方面的效果,在盆栽条件下,研究了纳米碳不同用量对烤烟根系生长发育、干物质积累和氮素吸收利用的影响。结果表明,在常规肥料中添加纳米碳能够促进烤烟根系生长发育,明显提高烟株根系活力和单株根系生物量,增加植株干物质积累量。施用纳米碳增加了烤烟植株成熟期各器官氮素含量和积累量,而未明显影响氮素在植株不同器官的分配。施用纳米碳不仅增加了植株对肥料氮的吸收量,还增加了对土壤氮的吸收量,这与其促进烤烟根系生长发育、提高根系吸收能力有密切关系。纳米碳无论做基肥还是做追肥,均显著提高了氮肥利用率,提高幅度分别达到14.44%和9.62%,有效降低了氮素土壤残留和损失。     

添加生化抑制剂和腐植酸的稳定性增效尿素在黄土中的施用效果

采用田间盆栽试验,研究生化抑制剂与生物刺激素腐植酸结合制成的高效稳定性增效尿素肥料在黄土中的氮素转化特征、增产效果和氮素肥料表观利用率,以探明其施用效果,为开发适宜黄土施用的新型增效尿素肥料提供理论依据。本研究以不施氮肥(CK)和施尿素氮肥(N)为对照,在尿素中分别添加腐植酸(F)、N-丁基硫代磷酰三胺(NBPT)、3,4-二甲基吡唑磷酸盐(DMPP)和2-氯-6-三甲基吡啶(CP),以及腐植酸与3种生化抑制剂分别组合(NBPT+F、DMPP+F、CP+F)。结果表明: 与N处理相比,F、NBPT+F、DMPP+F和CP+F处理均能显著提高玉米的产量、叶片叶绿素含量、叶面积指数和植株吸氮量,对土壤铵态氮和硝态氮含量也有显著影响。与单独施用生化抑制剂相比,添加腐植酸可提高玉米叶片叶绿素含量。与CP相比,CP+F玉米的植株吸氮量、叶绿素含量、氮肥吸收利用率均显著提高;与NBPT相比,NBPT+F硝化抑制率提高10.7%,但玉米产量、叶面积指数、植株吸氮量和氮肥利用率等均有所降低;与DMPP相比,DMPP+F显著降低了玉米产量、叶面积指数、植株吸氮量、氮肥利用率和硝化抑制率等。综合玉米产量、植株吸氮量、氮肥吸收利用率以及土壤铵态氮、硝态氮含量等指标,在黄土地区施用尿素肥料时,建议添加腐植酸和CP以提升尿素性能,从而提高产量和肥料利用率。     

控失尿素对稻田氨挥发、氮素转运及利用效率的影响

通过田间试验,以普通尿素分次施用处理(CU)为对照,研究了控失尿素分次施用(LCUS)和一次施用(LCUB)对水稻田土壤氨挥发特征、水稻氮素营养状况、稻谷产量及氮肥利用效率的影响. 结果表明: 普通尿素分次施用、控失尿素分次施用和控失尿素一次施用条件下,生育期氨挥发总量占总施氮量的比例分别为15.8%、13.4%和19.7%. 与普通尿素分次施用处理相比,控失尿素分次施用处理可降低土壤氨挥发损失量4.4 kg N·hm^-2,降幅达18.0%,而控失尿素一次施用处理稻田土壤氨挥发总量却增加了7.2 kg N·hm^-2,增幅达24.7%. 与普通尿素分次施用处理相比,控失尿素分次施用处理的水稻叶片叶绿素、籽粒和茎叶氮含量与氮素积累量、稻谷产量均有不同程度提高,氮肥利用率显著提高了7.6%,但氮素转运量、转运率和对穗氮贡献率均显著降低,而控失尿素一次施用处理的水稻叶片叶绿素、籽粒和茎叶氮含量与氮素积累量以及氮肥利用率均显著降低,氮素转运量、转运率、对穗氮贡献率以及稻谷产量无显著差异. 综上所述,控失尿素分次施用处理可以在保证稻谷稳产的同时,有效降低稻田土壤氨挥发损失,改善植株氮素营养状况,显著提高氮肥利用效率.     

Nitrogen use strategies of neotropical rainforest trees in threatened Atlantic Forest

The characteristics of nitrogen acquisition, transport and assimilation were investigated in species of an Atlantic Forest succession over calcareous soil in south‐eastern Brazil. Differences in behaviour were observed within the regeneration guilds. Pioneer species showed high leaf nitrogen contents, a high capacity to respond to increased soil nitrogen availability, a high capacity for leaf nitrate assimilation and were characterized by the transport of nitrate + asparagine. At the other end of the succession, late secondary species had low leaf nitrogen contents, little capacity to respond to increased soil nitrogen availability, low leaf nitrate assimilation and were active in the transport of asparagine + arginine. The characteristics of nitrogen nutrition in some early secondary species showed similarities to those of pioneer species whereas others more closely resembled late secondary species. Average leaf δ¹⁵N values increased along the successional gradient. The results indicate that the nitrogen metabolism characteristics of species may be an additional ecophysiological tool in classifying tropical forest tree species into ecological guilds, and may have implications for regeneration programmes in degraded areas.     

氮素形态及配比对夏播菘蓝生长及活性成分含量的影响

以来自山西的菘蓝(Isatis indigotica Fort.)为实验对象,采用盆栽法研究铵态氮(NH4+-N)、硝态氮(NO3--N)和酰胺态氮〔CO(NH2)2〕的不同配比对夏播菘蓝生长,叶和根中的可溶性蛋白质及总氮含量,根中多糖含量,叶中叶绿素相对含量,以及叶中靛玉红和靛蓝、根中(R,S)-告依春的含量和积累量的影响.结果表明:各施氮处理组的单株叶干质量均高于对照(不施用氮素)组,但单株根干质量或高于或低于对照组,其中,T4〔n(铵态氮):n(硝态氮):n(酰胺态氮)=25:75:0〕处理组的单株叶和根干质量均最大,且总体上显著高于对照组及其他施氮处理组(P<005);而施氮处理组的根冠比均显著低于对照组.各施氮处理组叶中的可溶性蛋白质含量与对照均无显著差异,但各施氮处理组根中的可溶性蛋白质含量、叶和根中的总氮含量以及叶中的叶绿素相对含量总体上显著高于对照组,而根中的多糖含量或高于或低于对照组,其中,T6〔n(铵态氮):n(硝态氮):n(酰胺态氮)=0:75:25〕处理组根中的多糖含量和叶中的叶绿素相对含量均最高,T3〔n(铵态氮):n(硝态氮):n(酰胺态氮)=50:50:0〕处理组叶和根中的可溶性蛋白质含量均较高.各施氮处理组叶中靛玉红含量总体上显著高于对照组,多数施氮处理组叶中靛蓝含量则显著低于对照组,但各施氮处理组的单株叶中靛蓝和靛玉红积累量总体上高于对照组;其中,T2〔n(铵态氮):n(硝态氮):n(酰胺态氮)=75:25:0〕处理组叶中靛玉红含量及其单株积累量均最高,T6处理组叶中靛蓝含量最高,而单株叶中靛蓝积累量则以T3处理组最高.各施氮处理组根中(R,S)-告依春含量总体上显著低于对照组,其中,以T1〔n(铵态氮):n(硝态氮):n(酰胺态氮)=100:0:0〕处理组根中(R,S)-告依春含量最高,T4处理组单株根中(R,S)-告依春积累量最高.综合分析结果表明:按不同配比施用不同形态氮素,夏播菘蓝的生长及活性成分含量有明显差异,因此,若以收获叶为目的,结合叶中靛玉红含量,建议施用铵态氮和硝态氮物质的量比为75:25的复合氮肥;若以收获根为目的,结合根中(R,S)-告依春含量,建议施用铵态氮和硝态氮物质的量比为25:75的复合氮肥.     

不同土壤水分条件下香樟凋落叶覆盖对土壤碳氮循环的影响

凋落物作为森林生态系统碳库的重要组成部分对森林土壤碳、氮循环具有重要作用.为探讨香樟凋落叶对土壤碳、氮循环的影响,室内模拟研究了10%、20%和30% 3种土壤含水量条件下香樟凋落叶覆盖森林土壤中碳、氮元素的变化.结果表明: 3种含水量条件下香樟凋落叶覆盖均显著增加了土壤CO₂排放速率和土壤溶解性有机碳(WSOC)含量,但显著降低了土壤中硝态氮含量,表明香樟凋落叶覆盖能够增强土壤呼吸强度和碳矿化,抑制土壤硝化作用;香樟凋落叶覆盖能够显著增加10%含水量土壤中铵态氮含量,但降低了20%和30%含水量土壤铵态氮含量,表明香樟凋落叶覆盖对土壤铵态氮含量的影响与土壤含水量有关.香樟凋落叶中部分单萜烯浓度在不同土壤含水量条件下分别与土壤CO₂排放速率和铵态氮含量呈显著正相关,而与土壤WSOC和硝态氮含量呈显著负相关,说明香樟凋落叶覆盖对土壤碳、氮循环的影响可能与凋落叶中的单萜烯有关.     

不同烤烟品种衰老叶片的无机氮积累及其生理调控

以不同烤烟品种‘红花大金元’和‘中烟100’为试验对象,研究同一生育期不同部位叶片的无机氮积累及其与氮素代谢和氨挥发的关系。结果表明,烟草植株下部衰老叶片（第5片叶）NO3^-和NH4^＋的含量要高于中部叶（第10和第15片叶）和上部叶（第20片叶）,并且‘红花大金元’下部叶NO3^-和NH4^＋的含量比‘中烟100’显著偏高;‘中烟100’植株各部位叶片的氨气补偿点比‘红花大金元’高。两个品种在第5到第20叶位间的谷氨酰胺合成酶（GS）、硝酸还原酶（NR）和谷氨酸脱氢酶（GDH）活性大小及其变化不一致,是叶片无机氮积累存在品种间差异的生理基础。     

A model of the acclimation of photosynthesis in the leaves of C3 plants to sun and shade with respect to nitrogen use

A model of leaf photosynthesis of C₃, plants has been developed to describe their nitrogen economy. In this model, photosynthetic proteins are categorized into five groups depending on their functions. The effects of investment of nitrogen in each of these groups on the maximal rate of photosynthesis and/or the initial slope of the light-response curve are described as simple equations. Using this model, the optimal pattern of nitrogen partitioning which maximizes the daily rate of CO₂ exchange is estimated for various light environments and leaf nitrogen contents. When the leaf nitrogen content is fixed, the amount of nitrogen allocated to Calvin cycle enzymes and electron carriers increases with increasing irradiance, while that allocated to chlorophyll-protein complexes increases with decreasing irradiance. For chlorophyll-proteins of photosystem II, the amount of light-harvesting complex II relative to that of the core complex increases with decreasing irradiance. At any irradiance, partitioning into ribulose bisphosphate carboxylase increases with increasing leaf nitrogen content Taking the total leaf nitrogen content and the daily CO₂ exchange rate as ‘cost’ and ‘benefit’, respectively, the optimal amount and partitioning of nitrogen are examined for various conditions of light environment and nitrogen availability. The leaf nitrogen content that maximizes the rate of daily carbon fixation increases with increasing growth irradiance. It is also predicted that, at low nitrogen availabilities, low leaf nitrogen contents are advantageous in terms, of nitrogen use efficiency. These trends predicted by the present model are largely consistent with those reported for actual plants. The differences in the total amount of leaf nitrogen and in the organization of photosynthetic components that have been reported for plants from different environments would therefore be of adaptive significance, because such differences can contribute to realization of efficient photosynthesis. These results are fürther discussed in an ecological context.     

不同海拔生境条件下水稻叶片及茎鞘氮素含量的变化

本文报道生长在不同海拔生境条件下(云南省元江、玉溪、昆明、大理、丽江)的水稻叶片及茎鞘氮素含量的变化。所获得的主要结果如下: 1.自然生境条件下,水稻叶片和茎鞘的氮素含量随着生育期的进展而变化,有一个由高到低的下降趋势。而前期低海拔地区的含量比高海拔地区的高,成熟期则是海拔越高其叶片含氮量也越高,茎鞘含氮量的情形与叶片相反。 2.穗肥施用时期不同,对叶片和茎鞘氮素含量的影响不同,在低和较低海拔地区施用时期越晚,成熟期残存于叶片及茎鞘的氮素就越多;而且海拔高的地区的含量也高。在冷凉的高海拔地区丽江以颖花分化期追肥比幼穗分化和减数分裂期施用则黄熟期保持较高的含氮量。     

Inorganic nitrogen assimilation in plants of Austrlian rainforest communities

In a study of the plant communities of two Australian rainforests, it was found that pioner species had high levels of nitrate reductase (EC 1.6.6.1) and were predominantly leaf nitrate assimilators. Under- and over-storey species had low levels of shoot and root nitrate reductase activity, and many of them showed little capacity for nitrate reduction even when nitrate ions were freely available. Although closed-forest species have lower levels of nitrate reductase than those of gaps and forest margins, their total nitrogen contents were similar, suggesting the former utilize nitrogen sources other than nitrate ions. Glutamine synthetase (EC 6.3.1.2) was present in the leaves of all species examined. In the leaves of pioneer species the chloroplastic isoform of glutamine synthetase predominted, while in most of the species typical of closed-forest the cytosolic isoform accounted for at least 40% of total leaf activity. Low levels of chloroplastic glutamine synthetase were correlated with a low capacity for leaf nitrate reduction, and both are characteristic of many species that regenerate and grow for some time in shade. Low levels of chloroplastic glutamine synthetase imply that, in some of these woody plants, photorespiratory ammonia is re-assimilated via cytosolic glutamine synthetase.     

不同施肥处理对甜菊生长及糖苷含量和积累量的影响

采用盆栽法,以甜菊( Stevia rebaudiana Bertoni)品种‘中山4号'(‘Zhongshan No.4')当年生扦插苗为研究对象,研究不同形态氮肥(硫酸铵、硝酸钠和尿素)及不同施氮量(纯氮)、施磷量( P2 O5)和施钾量( K2 O)对幼苗生长及糖苷含量和单株积累量的影响。结果显示：随氮肥、磷肥和钾肥施用量的提高,甜菊幼苗的株高、茎粗、叶长、叶宽、单株叶干质量和单株茎干质量均呈先升后降的变化趋势,且总体上与对照无显著差异,仅施磷量300 mg·kg-1处理组的叶长显著高于对照;根据施肥量与单株叶干质量的回归方程,确定硫酸铵、硝酸钠、尿素、磷肥和钾肥的施用量分别为64.87、660.21、735.84、211.54和775.92 mg·kg-1时,幼苗单株叶干质量最高。在硫酸铵处理组中,300 mg·kg-1处理组甜菊叶片中的莱鲍迪苷A( R-A)含量及甜菊苷( St)、R-A和总苷的单株积累量以及600 mg·kg-1处理组的St单株积累量高于对照,多数处理组的St、R-A和总苷含量及单株积累量均低于对照;在硝酸钠处理组中,1200 mg·kg-1处理组的R-A和总苷含量、600和900 mg·kg-1处理组的St单株积累量以及300~900 mg·kg-1处理组的R-A和总苷单株积累量高于对照,其他处理组的St、R-A和总苷含量及单株积累量均低于对照;在尿素处理组中,1500 mg·kg-1处理组的R-A和总苷的含量和单株积累量以及600和900 mg·kg-1处理组的R-A和总苷单株积累量高于对照,其他处理组的St、R-A和总苷含量及单株积累量均低于对照;各施氮处理组中,仅1500 mg·kg-1处理组的R-A含量与对照差异显著,其他指标均与对照无显著差异。在施磷处理组中,100 mg·kg-1处理组的R-A含量以及100和200 mg·kg-1处理组的St、R-A和总苷的单株积累量高于对照,多数处理组的St、R-A和总苷含量及单株积累量低于对照且与对照均无显著差异。在施钾处理组中,各处理组的St、R-A和总苷含量及单株积累量均高于对照,其中仅900 mg·kg-1处理组的St、R-A和总苷含量与对照显著差异。各施肥处理组的St含量占总苷含量的百分率均低于对照、R-A含量占总苷含量的百分率均高于对照,且总体上与对照无显著差异。经过综合分析,建议在甜菊生育期内的施肥量为纯氮600~900 mg·kg-1、P2 O5200~300 mg·kg-1和K2 O 600~900 mg·kg-1,其中氮肥以尿素为宜。     

Effects of leaf age,nitrogen nutrition and photon flux density on the distribution of nitrogen among leaves of a vine (Ipomoea tricolor Cav.) grown horizontally to avoid mutual shading of leaves

Effects of leaf age, nitrogen nutrition and photon flux density (PFD) on the distribution of nitrogen among leaves were investigated in a vine, Ipomoea tricolor Cav., which had been grown horizontally so as to avoid mutual shading of leaves. The nitrogen content was highest in newly developed young leaves and decreased with age of leaves in plants grown at low nitrate concentrations and with all leaves exposed to full sunlight. Thus, a distinct gradient of leaf nitrogen content was formed along the gradient of leaf age. However, no gradient of leaf nitrogen content was formed in plants grown at a high nitrate concentration. Effects of PFD on the distribution of nitrogen were examined by shading leaves in a manner that simulated changes in the light gradient of an erect herbaceous canopy (i.e., where old leaves were placed under increasingly darker conditions with growth of the canopy). This canopy-type shading steepened the gradient of leaf nitrogen content in plants grown at a low nitrogen supply, and created a gradient in plants grown at high concentrations of nitrate. The steeper the gradient of PFD, the larger the gradient of leaf nitrogen that was formed. When the gradient of shading was inverted, that is, younger leaves were subjected to increasingly heavier shade, while keeping the oldest leaves exposed to full sunlight, an inverted gradient of leaf nitrogen content was formed at high nitrate concentrations. The gradient of leaf nitrogen content generated either by advance of leaf age at low nitrogen availability, or by canopy-type shading, was comparable to those reported for the canopies of erect herbaceous plants. It is concluded that both leaf age and PFD have potential to cause the non-uniform distribution of leaf nitrogen. It is also shown that the contribution of leaf age increases with the decrease in nitrogen nutrition level.     

Optimal leaf area indices in C3 and C4 mono- and dicotyledonous species at low and high nitrogen availability

From an analytical model it was shown that for a given total amount of nitrogen in the canopy, there exists an optimal leaf area index (LAI), and therefore an optimal average leaf introgen content, at which canopy photosynthesis is maximal. If the LAI is increased above this optimum, increased light interception will not compensate for reduction in photosynthetic capacity of the canopy resulting from reduced leaf nitrogen contents. It was further derived from the model that the value of the optimal LAI increases with the photosynthetic nitrogen use efficiency (PNUE) and decreases with the canopy extinction coefficient for light (K_L) and incident photon flux density (PFD) at the top of the canopy. These hypotheses were tested on dense stands of species with different photosynthetic modes and different architectures. A garden experiment was carried out with the C₄ monocot sorghum ( Sorghum bicolor [L.] Moensch cv. Pioneer), the C₃ monocot rice ( Oryza sativa L. cv. Araure 4), the C₄ dicot amaranth ( Amaranthus cruentus L. cv. K113) and the C₃ dicot soybean ( Glycine max [L.] Merr. cv. Williams) at two levels of nitrogen availability.
The C₄ species had higher PNUEs than the C₃ species while the dicots formed stands with higher extinction coefficients for light and had lower PNUEs than the monocots. The C₄ and monocot species were found to have formed more leaf area per unit leaf nitrogen (i.e., had lower leaf nitrogen contents) than the C₃ and dicot species, respectively. These results indicate that the PNUE and the extinction coefficient for light are important factors determining the amount of leaf area produced per unit nitrogen as was predicted by the model.