A dynamic model for nitrogen-stressed lettuce

A previously developed dynamic lettuce model, designed to predict growth and nitrate content under the normal range of glasshouse environmental conditions, has been extended to cover high nitrogen-stress situations. Under severe shortage of nitrogen, lettuce has been observed to grow at a very slow rate, as well as to have abnormally low water content, low reduced-nitrogen content and negligible nitrate content. The new model mimics these observations by adding to the original model a storage compartment for 'excess' carbon. The resulting model has three compartments: (1) 'vacuole', where the soluble non-structural material is stored, and the nitrate : carbon ratio may vary as needed to maintain a constant osmotic potential; (2) 'structure', a metabolically active compartment with fixed chemical composition; and (3) 'excess-carbon', which serves as a long-term storage of 'waterless' carbohydrates. Simulations with the model illustrate its ability to predict the effect of light, temperature and nitrogen in the nutrient solution on the long-term growth and composition of lettuce. They also illustrate the effects of plant size, and the associated relative growth rate, on the characteristic times of transient responses resulting from step changes in the environment.     

Nitrate accumulation in plants: a role for water

Plant nitrate and water contents (g^-1 dry weight) were monitored (1) in tomato plants in a growth room, during the day/night cycle with varied light intensities; (2) in two lettuce cultivars during the day/night cycle in a growth room and during growth in a glasshouse. Large, concurrent, and linearly correlated changes in nitrate and water contents were observed in both species and time-scales. Although these changes were dependent on light intensity and other environmental conditions, the slope of their relationship was not affected. Furthermore, when a limiting nitrate nutrition regime was applied to tomato, a significant and concurrent reduction of both plant nitrate and water contents was observed. Thus, when compared on the same water content basis, their nitrate content was only slightly reduced. These nitrate and water content changes were also observed in plant parts, and confirmed, through data extracted from the literature, in a large number of species (annuals and perennials) and other environments (open-field, soil culture). They are interpreted as an effect of homoeostasis for endogenous nitrate concentration (mol m^-3), and it is suggested that nitrate content changes (mol g^-1 dry wt.) result from the varying size of a water reservoir (m³ g^-1 dry wt.) whose nitrate concentration is regulated. From this viewpoint, the concept of critical nitrate concentration is discussed, and it is proposed to introduce explicitly water content in plant nitrogen models.Keywords: Nitrate content, water content, homoeostasis.      

LED短期连续光照与氮营养对水培生菜品质的影响

设置10和15 mmol·L^-12个氮水平处理,NO₃^- -N∶NH₄⁺-N比例分别为1∶0、4∶1和1∶1的3个氮形态处理,水培紫叶生菜,研究其在LED红蓝组合光短期连续光照(SCL)后的品质提升效果.结果表明： 各处理生菜地上部干质量在LED光源SCL处理后均显著提高,最小增幅为35.1%,根系干质量除NO₃^- -N∶NH₄⁺-N为1∶1且氮水平为15 mmol·L^-1的处理和NO₃^- -N∶NH₄⁺-N为1∶0且氮水平为10 mmol·L^-1的处理外,差异都达到显著水平.SCL处理前,不同氮营养处理生菜总酚、类黄酮相对含量差异不显著.SCL处理后,不同氮营养条件下生菜总酚、类黄酮和花青素相对含量差异显著.2种氮水平下,总酚和类黄酮相对含量随铵氮比例的提高而增加,花青素相对含量随铵氮比例增加而先降低后升高.SCL处理使生菜叶片、叶柄硝酸盐含量显著降低,其中叶片硝酸盐含量降低23.2%,生菜叶片抗坏血酸、可溶性糖和可溶性蛋白含量均显著提高.叶片硝酸盐含量降低速率随氮水平和铵氮比例的增加而提高.抗坏血酸含量增加速率主要受氮水平影响,氮水平较低时抗坏血酸含量增加速率较高.可溶性糖含量增加速率随着铵氮比例的增加而增加.SCL处理显著提高了不同氮营养水培生菜干物质的积累,同时显著降低了硝酸盐的积累,显著提高了抗坏血酸、可溶性糖和可溶性蛋白含量,氮营养条件对SCL改善生菜品质的速率有显著影响.     

莴笋对不同形态氮素的反应

探讨了不同形态氮素对莴笋生长发育的影响及其营养特性。结果表明,莴笋幼苗根系对NH4^+ -N的亲和力稍大于NO3^- -N的亲和力;分别供给NO3^- -N+NO3^- -N及NH4^+ -N,莴笋的生物学产量和吸N量均依次递减（分别为100：56.9：12.4,100：48.9：8.6）,因此在水培条件下,NO3^- -N是最适合莴笋生长发育的氮源,NH4^+ -N与NO3^- -N各占50％时对莴笋的生长发育已有一定的抑制作用,仅以NH4^+ -N作氮源则莴笋很难生长;NH4^+ -N与NO3^- -N各占50％时,莴笋倾向于吸收较多的NH4^+ -N,而且在培养不同阶段NH4^+/NO3^-吸收比例均大于1,莴笋表现出喜铵性,但NH4^+ -N并非莴笋很适合的氮源;营养液中NO3^- -N不足,主要影响莴笋茎叶的生长,而NH4^+ -N所占比例达50％时,莴笋根系生长受到抑制,且有明显的受害症状;以NO3^- -N作氮源预培养两周,以含微量NO3^- -N的自来水为水源,再单独以NH4^+ -N为氮源,对莴笋生长有极大的促进作用,同时还大幅度降低了体内硝酸盐的含量。尿素作氮源莴笋未出现受害症状,但莴笋的生长发育状况明显劣于其它氮源。     

Leaf age as a risk factor in contamination of lettuce with Escherichia coli O157:H7 and Salmonella enterica

Outbreaks of Escherichia coli O157:H7 infections have been linked increasingly to leafy greens, particularly to lettuce. We present here the first evidence that this enteric pathogen can multiply on the leaves of romaine lettuce plants. The increases in population size of E. coli O157:H7 in the phyllosphere of young lettuce plants ranged from 16- to 100-fold under conditions of warm temperature and the presence of free water on the leaves and varied significantly with leaf age. The population size was consistently ca. 10-fold higher on the young (inner) leaves than on the middle leaves. The growth rates of Salmonella enterica and of the natural bacterial microflora were similarly leaf age dependent. Both enteric pathogens also achieved higher population sizes on young leaves than on middle leaves harvested from mature lettuce heads, suggesting that leaf age affects preharvest as well as postharvest colonization. Elemental analysis of the exudates collected from the surfaces of leaves of different ages revealed that young-leaf exudates were 2.9 and 1.5 times richer in total nitrogen and carbon, respectively, than middle-leaf exudates. This trend mirrored the nitrogen and carbon content of the leaf tissue. Application of ammonium nitrate, but not glucose, to middle leaves enhanced the growth of E. coli O157:H7 significantly, suggesting that low nitrogen limits its growth on these leaves. Our results indicate that leaf age and nitrogen content contribute to shaping the bacterial communities of preharvest and postharvest lettuce and that young lettuce leaves may be associated with a greater risk of contamination with E. coli O157:H7.     

施用猪粪对油麦菜产量、硝酸盐含量及土壤养分的影响

应用盆栽试验方法,研究了施用猪粪对西南地区黄壤和紫色土中油麦菜产量、硝酸盐含量及土壤养分的影响.结果表明:施用猪粪能显著提高油麦菜产量,且黄壤中油麦菜增产幅度大于紫色土;油麦菜中硝酸盐、氮磷钾含量与土壤类型及猪粪施用量密切相关,以中国农业科学院制定的蔬菜中硝酸盐污染程度评价标准为依据,在紫色土对照(CK)及1倍猪粪(相当于施纯N 200 kg·hm^-2)处理下油麦菜硝酸盐含量较低,符合一级标准(≤432 mg·kg^-1,轻度污染);其他处理多超过二级标准(≤758 mg·kg^-1,中度污染),但均未超过三级标准(≤1440 mg·kg-¹,重度污染);黄壤中除化肥和8倍猪粪(相当于施纯N 1600 kg·hm^-2)处理下油麦菜硝酸盐含量超过二级标准外,其他各处理均符合一级标准;黄壤和紫色土中表征磷素淋失风险的有效磷临界值分别为96.3和107.7 mg·kg^-1.黄壤的猪粪环境安全容量较紫色土高.施用猪粪能显著提高两种土壤的有机碳和全氮含量.     

The effects of host carbon dioxide, nitrogen and water supply on the infection of wheat by powdery mildew and aphids

In two experiments, winter wheat (Triticum aestivum cv. Cerco) was grown in 350 (ambient) and 700 μmol mol^-1 (elevated) atmospheric CO₂ concentrations. In the first experiment, plants were grown at five levels of nitrogen fertilization, and in the second experiment, plants were grown at three levels of water supply. All plants were infected with powdery mildew, caused by the fungus Erysiphe graminis. Plants grown in elevated atmospheric CO₂ concentrations had significantly reduced % shoot nitrogen contents and significantly increased % shoot water contents. At elevated atmospheric CO₂ concentrations, where plant nitrogen content was significantly reduced, the severity of mildew infection was significantly reduced, and where host water content was significantly increased, the severity of mildew infection was significantly increased. In a moderate water supply treatment, the plants grown in elevated atmospheric CO₂ concentrations had significantly reduced nitrogen contents (9·9%) and significantly increased water content (4%), the amount of mildew infection was unchanged. The severity of mildew infection appeared to be more sensitive to host water content than to host nitrogen content.     

不同施氮量对乌龙茶生长和生理的影响

以武夷肉桂为研究对象,研究不同施氮量对乌龙茶幼龄茶树生长和生理的影响。结果表明,幼龄茶树对氮肥的需求不强烈,其新梢生物量、根生物量和总生物量以及茶叶产量随施氮量的增加而下降。茶树新梢全氮、叶绿素、游离氨基酸、茶多酚和咖啡碱的含量随施氮量的增加而增加,而茶树碳氮比随着施氮量增加而下降;但施氮并没有影响茶树总碳含量。老叶叶绿素含量、根全氮和硝态氮含量、新梢总糖含量与施氮量呈二次曲线回归关系,适度施氮促进根对氮的吸收、老叶叶绿素合成和新梢总糖代谢,过度施氮则相反。新梢生物量与其硝态氮含量和游离氨基酸总量显著负相关;根生物量与根碳氮比和新梢咖啡碱含量显著负相关;茎叶生物量和总生物量与根含氮量显著正相关,但与新梢硝态氮和氨基酸含量显著负相关。过度施氮造成茶树生产力下降的主要原因是因为过度施氮极显著提高了茶树氨基酸代谢水平,使用于茶树生长的碳代谢产物（如总糖）减少,进而影响茶树的生长。     

长江中游浅水湖泊水生植物氮磷含量与水柱营养的关系

水生植物组织内氮和磷(N和P)含量受到水体营养状况和植物生长状况影响。对长江中游江汉湖群不同营养水平湖泊中大型水生植物的N和P含量3个季度的研究表明,在不同生活型水生植物中,沉水植物主要分布在中营养到中富营养湖泊中,在富营养湖泊均无分布,浮叶和挺水植物在不同营养类型湖泊的沿岸带均有分布。N和P含量以沉水植物最高,浮叶植物次之,挺水植物最低。水生植物的N和P含量都达到或超过生长所需最低N和P阈值,代表性浮叶植物和沉水植物的N和P含量随着湖泊营养水平提高呈现规律性变化。湖泊5种常见的水生植物N和P含量与水柱中不同种类N和P浓度具有季节性相关:菱(TrapabispinosaRoxb.)春夏季P含量都与TP(总磷)和TDP(总溶解磷)明显相关,春季N含量与NH4—N(氨氮)明显相关;春季黄丝草(PotamogetonmaackianusA.Benn.)的P含量与TP明显相关,夏季与TDP明显相关,春季和夏季黄丝草和穗花狐尾藻(MyriophyllumspicatumL.)的N含量与TN(总氮)和TDN(总溶解氮)显著正相关,秋季成负相关;夏季芦苇(PhragmitescommunisTrin.)P含量与TP和TDP显著相关;春季芦苇和香蒲(TyphaorientalisPresl.)N含量与NH4N和NO2N(亚硝态氮)显著相关。       

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.     

Nitrogen Fixation and Nitrogen Assimilation in a Temperate Saline Ecosystem

As nitrogen is known to be a limiting factor for plant growth, we were interested in the relationship between soil microbial activity and the nitrogen assimilation of 5 different halophytes from 4 saline sites near the lake “Neusiedlersee”, Austria. The following were studied between May and October 1985: nitrogen fixation (¹⁵N₂ and acetylene reduction): N-mineralization; several soil characteristics and in vivo nitrate reductase activity of roots and shoots of these plants. NO^?₃, org. N- and carboxylate contents of both roots and shoots, as well as the effect of NO^?₃-fertilization on the amounts of these substances, were determined on plants growing in the field during a 3-day period in September 1985. Fertilization led to a decrease in acetylene reduction activity at most sites, and an increase in the nitrate reductase activity of the shoots of all plants. Overall, carboxylate and organic nitrogen contents of these halophytes did not change in response to fertilization. Only in the roots of Aster tripolium and Atriplex hastata was there a marked increase in the nitrate reductase activity in response to fertilization. Species growing at the same site, such as Plantago maritima and Lepidium crassifolium showed contrasting levels of assimilatory activity. Apparent low rates of ammonification and nitrification were detected in soils from the 4 sites. The results are discussed in relation to the nitrogen and carbon economies of the microorganisms and plants.     

Distribution of dry weight between root and shoot in white clover dependent on N2 fixation or utilizing abundant nitrate nitrogen

Summary Plants of white clover var. Blanca were grown singly in pots in controlled environments, or in small swards in a glasshouse, to determine how their distribution of dry weight between root and shoot was influenced when they were dependent on N₂ fixation in their root nodules or when they lacked nodules but utilized an abundant supply of nitrate nitrogen. In single plants and in swards, changes in root/shoot ratio with increasing age and plant development were not influenced by the source of nitrogen, but nodulated plants always displayed a higher root/shoot ratio. When nodulated plants were supplied with nitrate nitrogen, root/shoot ratio declined to values intermediate between those of nodulated and of nitrate plants. The results are discussed in relation to the persistence of white clover, and the general level of productivity, in grass-clover swards. The Grassland Research Institute is financed through the Agricultural Research Council.     

Interaction of sulfur and nitrogen nutrition in tobacco (Nicotiana tabacum) plants: significance of nitrogen source and root nitrate reductase

Abstract: The significance of root nitrate reductase for sulfur assimilation was studied in tobacco (Nicotiana tabacum) plants. For this purpose, uptake, assimilation, and long-distance transport of sulfur were compared between wild-type tobacco and transformants lacking root nitrate reductase, cultivated either with nitrate or with ammonium nitrate. A recently developed empirical model of plant internal nitrogen cycling was adapted to sulfur and applied to characterise whole plant sulfur relations in wild-type tobacco and the transformant. Both transformation and nitrogen nutrition strongly affected sulfur pools and sulfur fluxes. Transformation decreased the rate of sulfate uptake in nitrate-grown plants and root sulfate and total sulfur contents in root biomass, irrespective of N nutrition. Nevertheless, glutathione levels were enhanced in the roots of transformed plants. This may be a consequence of enhanced APR activity in the leaves that also resulted in enhanced organic sulfur content in the leaves of the tranformants. The lack of nitrate reductase in the roots in the transformants caused regulatory changes in sulfur metabolism that resembled those observed under nitrogen deficiency. Nitrate nutrition reduced total sulfur content and all the major fractions analysed in the leaves, but not in the roots, compared to ammonium nitrate supply. The enhanced organic sulfur and glutathione levels in ammonium nitrate-fed plants corresponded well to elevated APR activity. But foliar sulfate contents also increased due to decreased re-allocation of sulfate into the phloem of ammonium nitrate-fed plants. Further studies will elucidate whether this decrease is achieved by downregulation of a specific sulfate transporter in vascular tissues.     

横断山区草本沼泽湿地水体氮含量空间分布特征

草本沼泽是横断山区重要的湿地类型,为探明横断山区草本沼泽湿地水体中总氮、硝氮和氨氮的空间分布特征及其控制因素,于2014—2017年在横断山区对典型草本沼泽湿地开展水样采集和分析工作,同时收集降水量、地表大气温度、水温、水深、人口数量、GDP、家畜数量等环境数据。结果表明：1）横断山区草本沼泽湿地水体中总氮含量表现出明显的纬向地带性和垂直地带性：总氮含量随纬度和海拔增加而下降,水温是控制这种地带性特征的主要因素。同时,随经度增加,水体中总氮含量也显著增加,社会经济发展因素是导致这种分布特征的主要原因;2）横断山区沼泽湿地水体中硝氮和氨氮含量在海拔梯度上的变化趋势不明显;3）随经度和纬度增加,沼泽湿地水体中硝氮含量逐渐增加,导致这种现象的主要原因是水深和水温;4）随经度增加,沼泽湿地水体中氨氮的含量逐渐增加,但氨氮含量与自然环境因素和社会经济发展因素均无显著相关性。     

Quantitative trait loci analysis of water and anion contents in interaction with nitrogen availability in Arabidopsis thaliana

In plants, water and anion parameters are linked, for example through the integration of nutritional signaling and the response to diverse stress. In this work, Arabidopsis thaliana is used as a model system to dissect the genetic variation of these parameters by quantitative trait loci (QTL) mapping in the 415 recombinant inbred lines of the Bay-0 x Shahdara population. Water, nitrate, chloride, and phosphate contents were measured at the vegetative stage in the shoots of plants grown in controlled conditions. Two contrasting nitrogen (N) conditions were studied, one leading to the complete depletion of the nitrate pool in the plants. Most of the observed genetic variation was identified as QTL, with medium but also large phenotypic contributions. QTL colocalization provides a genetic basis for the correlation between water and nitrate contents in nonlimiting N conditions and water and chloride contents in limiting N conditions. The 34 new QTL described here represent at least 19 loci polymorphic between Bay-0 and Shahdara; some may correspond to known genes from water/anion transport systems, while others clearly identify new genes controlling or interacting with water/anion absorption and accumulation. Interestingly, flowering-time genes probably play a role in the regulation of water content in our conditions.     

The effect of rhizoctonia root disease and applied nitrogen on growth,nitrogen uptake and nutrient concentrations in spring wheat

Root disease caused by Rhizoctonia solani is a common problem of spring wheat in South Australia. There are reports that nitrogen applications can reduce the incidence and severity of the disease. A glasshouse trail in pots examined the effects of disease and of applied nitrogen on wheat growth, and evaluated the utility of the basal stem nitrate concentration in diagnosing deficiency in plants with and without root disease. Plants were harvested at the mid-tillering stage. Shoot growth was increased by applied nitrogen until a maximum yield was attained, after which additional N had no effect on shoot yield. Root growth, however, responded positively only to low levels of applied N, after which it declined, and in the highest N treatment root mass was less than in the plants without applied N. Root disease caused severe reductions in plant growth, and both root and shoot mass were affected similarly. Even though growth of diseased plants responded positively to applied nitrogen the response was less than that of disease-free plants. The critical concentration of basal stem nitrate-N did not appear to be affected by root disease, and was estimated at 1200 mg kg^-1, consistent with other glasshouse data. The basal stem nitrate-N concentration, either in fresh or dried tissue, appeared a better diagnostic tool of N stress than did total shoot N concentration or content, because of sharper definition of critical concentrations. Concentrations of other nutrients in shoot tissue were affected differentially by both applied nitrogen and root disease, but generally did not reach critical levels, although phosphorus and magnesium appeared deficient in very disease-stressed plants.     

不同氮素水平对油麦菜栽培效果的综合评价分析

为探讨不同氮素水平的硝态氮与铵态氮对油麦菜(Lactuca sativa L.)生长及品质的影响,自主设计并制作了适合蔬菜水培的立体管道栽培系统,配制了NO3-：NH4+=10：0,NO3-：NH4+=7：1,NO3-：NH4+=7：3的营养液,通过模糊数学原理,采用层次分析法(AHP)确定品质的权重值,综合评价了不同氮素水平对油麦菜的栽培效果。结果表明,以NO3-：NH4+=7：3营养液的栽培效果最好,其次是NO3-：NH4+=7：1。当营养液的NO3-：NH4+=7：3时,油麦菜的产量最高,叶片叶绿素、可溶性糖、可溶性蛋白质含量最高,硝酸盐含量最少,其综合品质最好。层次分析法对油麦菜不同氮素水平营养液的栽培效果的综合评价有较好的适用性,有助于获得南方设施管道栽培油麦菜最佳的营养液配方。     

Effects of different LED sources on the growth and nitrogen metabolism of lettuce

Using a light-emitting diode (LED) as the light source, the effects of eight different light treatments [white light (control, W), purple light (P), blue light (B), red light (R), green light (G), yellow light (Y), red–blue light in a 9:1 ratio (9R/1B), and red–blue light in a 4:1 ratio (4R/1B)] on the growth, quality and nitrogen metabolism of lettuce were studied. The results showed that compared with the white light, the purple light, blue light, red light, and the red-blue light combination could all increase the biomass of the aboveground part of lettuce to various degrees, while green light and yellow light inhibited lettuce growth. Under blue light, the contents of soluble protein and flavonoid in lettuce were the highest; under red light, the soluble sugar content was the highest, while the contents of soluble protein, free amino acids, and vitamin C (VC) were relatively higher under the 4R/1B light condition. Compared with white light, the sources of purple, blue, and red lights as well as the red–blue light combination all significantly reduced nitrate accumulation in lettuce, and the activities of the nitrogen (N) metabolism-related enzymes such as nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase were increased to varying degrees. In contrast, the contents of nitrate and ammonium N were significantly accumulated in lettuce under green light, and the activities of relative enzymes were significantly reduced. Therefore, the purple light, blue light, and red–blue combination light sources could promote N assimilation and improve the aboveground biomass accumulation in lettuce by improving the activity of the N metabolism-related enzymes in lettuce. Particularly under the 4R/1B light source, the biomass, soluble protein, VC, and total amino acid content were rather high in lettuce, which indicated that the 4R/1B light source could better effectively improve the nutritional quality and promote the growth of lettuce, while yellow light and green light are not suitable to serve as direct sources in a plant factory. These results provide a certain theoretical basis for the regulation of the light environment in cultivation facilities.     

Plant water stress and previous herbivore damage affect insect performance

1. Short‐term changes in plant resistance traits can be affected by abiotic factors or damage by herbivores, although how the combined effects of abiotic factors and previous damage affect subsequent insect larval development is not well understood. 2. Complementary glasshouse and field experiments were conducted to evaluate whether plant water stress and previous herbivore damage influenced monarch (Danaus plexippus) larval development on common milkweed, Asclepias syriaca. 3. In the glasshouse, water stress altered a suite of A. syriaca functional traits but did not affect nutrient content, whereas herbivore damage increased leaf nitrogen (N) and reduced the carbon:nitrogen (C:N) ratio. A bioassay experiment showed that monarch larval survival was lower on well‐watered plants that were previously damaged by monarch larva than on damaged and drought‐stressed plants. Bioassay larvae consumed less leaf tissue of previously damaged plants, whereas monarch larval mass was affected additively by water stress and previous damage, after correcting for the amount of leaf tissue consumed. 4. In a 2‐year field experiment, monarch larval performance was higher on previously damaged A. syriaca plants that received experimentally reduced rainfall, relative to plants receiving ambient rainfall. 5. Collectively, these results from glasshouse and field experiments suggest that insect performance was highest on previously damaged plants under water stress and highlight the additive and interactive roles of abiotic and biotic factors on herbivore performance.     

Growth and nitrogen metabolism of Catasetum fimbriatum (orchidaceae) grown with different nitrogen sources

Catasetum fimbriatum is an epiphytic orchid from South America that has been used for 15 years as a model plant for metabolic and developmental studies in our laboratory. In this work, C. fimbriatum plants were aseptically grown with 6 mol m(-3) of either glutamine or inorganic nitrogen forms (NO(3)(-):NH(4)(+) ratios). The highest biomass accumulation was found in plants supplied with glutamine; no significant difference was observed in plants incubated in the presence of inorganic nitrogen sources. Nitrogen assimilation was limited in the presence NO(3)(-) as a sole nitrogen source. C. fimbriatum did not accumulate NO(3)(-) and very low rates of in vivo nitrate reductase activity were observed. Most nitrate reductase activity (70%) was detected in the 2 cm apical roots. Nitrate-treated plants exhibited relatively lower amounts of free amino-N, chlorophyll and free NH(4)(+) contents and higher soluble sugar contents than the NH(4)(+)-treated plants. While shoot glutamine synthetase activity was only slightly affected by nitrogen sources, root glutamine synthetase activity was not modified by any nitrogen form. Glutamate dehydrogenase-NADH activity in shoot tissues was not influenced by any nitrogen source. However, the glutamate dehydrogenase-NADH activity in roots was enhanced when NH(4)(+) tissue contents was augmented by increasing NH(4)(+) in the medium and by the presence of glutamine. Our results strongly suggest that organic nitrogen and NH(4)(+) are probably the most important nitrogen sources to C. fimbriatum plants.