Postharvest responses of hydroponically grown lettuce varieties to nitrogen application rate

Limited information is available on the influence of preharvest N application rates on postharvest quality of different lettuce genotypes. Two green leafy lettuce(Multigreen 1 and Multigreen 3) and red leafy lettuce(Multired 4) were grown in gravel film technique and fertigated with five different N application rates: 60, 90, 120, 150 and 180 mg L~(–1). The 120 mg L~(–1) N application is commercially recommended for lettuce. After harvest, lettuce samples were packed in a bioriented poly propylene packaging(5% O_2 and 5% CO_2) and held at 5°C and 85% RH for 3, 6, 9 and 12 days. The genotypes, preharvest N application rates and storage time affected the leaf colour coordinates, phenolic acids(dicaffeoyltataric acid, caffeoyl tartaric acid, 3-caffeoylquinic acid and 3,4-dihydroxycinnamic acid) and browning enzyme activities(phenylalanine ammonia-lyase(PAL), polyphenol oxidase(PPO) and peroxidase(POD)). Lower rates of N application at preharvest stage showed higher weight loss with the storage time increasing in Multigreen 3. In Multigreen 1, colour coordinate b* value decreased remarkably with N application rates from 60 to 120 mg L~(–1) due to the onset of browning during storage. While in Multigreen 3 and N application higher than 60 mg L~(–1) influenced the decrease in b* value. Browning occurred due to the increased activity of PAL enzyme and the availability of the substrates caftaric, chlorogenic, caffeic acids, PPO activity and production of browning pigments due to the activity of POD. Higher, N application rates(120 mg L~(–1)) influenced the browning mechanism and showed brownish red leaves in Multired 4 during storage. Higher ascorbic acid concentration played a role in reducing the onset of browning in the fresh cuts leaves of Mulitired 4 and Multigreen 3 fertilized with lower preharvest lower N application rates(120 mg L~(–1)). Preharvest N application at 90 mg L~(–1) retained the colour, ascorbic acid content and the phenolic acid components and extended the shelf life of Multired 4 lettuce up to 6 days.     

The positive function of selenium supplementation on reducing nitrate accumulation in hydroponic lettuce (Lactuca sativa L.)

High nitrate(NO_3~- ) in vegetables, especially in leaf vegetables poses threaten to human health. Selenium(Se) is an important element for maintaining human health, and exogenous Se application during vegetable and crop production is an effective way to prevent Se deficiency in human bodies. Exogenous Se shows positive function on plant growth and nutrition uptake under abiotic and/or biotic stresses. However, the influence of exogenous Se on NO_3~- accumulation in hydroponic vegetables is still not clear. In the present study, hydroponic lettuce plants were subjected to six different concentrations(0, 0.1, 0.5, 5, 10 and 50 μmol L–1) of Se as Na2 Se O3. The effects of Se on NO_3~- content, plant growth, and photosynthetic capacity of lettuce(Lactuca sativa L.) were investigated. The results showed that exogenous Se positively decreased NO_3~- content and this effect was concentration-dependent. The lowest NO_3~- content was obtained under 0.5 μmol L–1 Se treatment. The application of Se enhanced photosynthetic capacity by increasing the photosynthesis rate(Pn), stomatal conductance(Cs) and the transpiration efficiency(Tr) of lettuce. The transportation and assimilation of NO_3~- and activities of nitrogen metabolism enzymes in lettuce were also analysed. The NO_3~- efflux in the lettuce roots was markedly increased, but the efflux of NO_3~- from the root to the shoot was decreased after treated with exogenous Se. Moreover, Se application stimulated NO_3~- assimilation by enhancing nitrate reductase(NR), nitrite reductase(Ni R), glutamine synthetase(GS) and glutamate synthase enzyme(GOGAT) activities. These results provide direct evidence that exogenous Se shows positive function on decreasing NO_3~- accumulation via regulating the transport and enhancing activities of nitrogen metabolism enzyme in lettuce. We suggested that 0.5 μmol L–1 Se can be used to reduce NO_3~- content and increase hydroponic lettuce yield.     

LED绿光补光模式对生菜生长及品质的影响

【目的】探究不同光照强度以及补光模式的绿光对植物工厂中水培生菜生长及营养品质的影响,为绿光的供光策略提供参考。【方法】以8:00—20:00照射的强度为160μmol·m~(-2)·s~(-1)的LED白光(W)为基础光,在保证生菜正常生长的前提下,补充3种不同强度(30、60、90μmol·m~(-2)·s~(-1))的绿光(G),并通过调节绿光的供光时间点使之与基础白光形成重叠(O)和不重叠(N)两种供光模式,分别为W、WG30O、WG60O、WG90O、WG30N、WG90。N共6个处理,各处理间绿光补光时长均为6 h。【结果】除处理WG90N外,其他补充绿光的处理较对照W均显著提高了生菜地上部鲜重,且30μmol·m~(-2)·s~(-1)的低强度绿光更有利于生菜的生长及生物量积累;补充绿光的处理均不同程度的提高了生菜可溶性糖、粗蛋白以及Vc含量,同时降低了硝酸盐含量,其中,生菜可溶性糖、粗蛋白以及Vc含量随着绿光补光强度的升高而增加;绿光在作用于生菜生物量积累过程中依赖于背景白光,而在作用于可溶性糖积累和Vc合成过程中与背景白光的关系不显著。【结论】绿光对生菜的作用效果与绿光补光强度及其相对于基础光的供光模式有关,且对于不同的目的指标,绿光补光效果有所差异,在实际生产中可根据生产目的建立不同的绿光补光策略。     

Interactive Effect of GA3, N and P Ameliorate Growth,Seed and Fibre Yield by Enhancing Photosynthetic Capacity and Carbonic Anhydrase Activity of Linseed: A Dual Purpose Crop

Linseed (Linum usitatissimum L.) is an important dual-purpose, industrial crop. Its seeds are used for the extraction of oil and stem for fibres. However, the production of linseed is not going parallel with the increasing demand of its products. The present work was carried out with an aim to find out whether exogenous application of gibberellic acid (GA₃) with or without graded levels of nitrogen (N) and phosphorus (P) could improve the performance of three linseed genotypes Parvati, Shekhar and Shubhra together with minimizing the costly fertilizer input and losses. Four combinations of N and P, viz., 0 mg N+0 mg P kg^?1 soil (N₀P₀), N_13.4P_4.46, N_26.8P_8.94 and N_40.2P_13.4 were constituted. Half dose of each combination was applied basally at the time of sowing and remaining half dose was given at 40 d after sowing (DAS) as foliar spray along with 10^?6 mol L^?1 GA₃. Prior to sowing, the seeds of each linseed genotype were grouped in to two, one group of seeds was soaked in 0 mol L^?1 GA₃ (control) and the other group was soaked in 10^?6 M GA₃ solution, each for 8 hours. Treatments were comprised of (i) 0 mol L^?1 GA₃+N₀P₀ (T₀, control), (ii) 10^?6 mol L^?1 GA₃ + N₁₃₄P₄₄₆ (T₁), (iii) 10^?6 mol L^?1 GA₃+N_26.8P_8.94 (T₂) and (iv) 10^?6 mol L^?1 GA₃+N_40.2P_13.4 (T₃). The crop performance was assessed in terms of growth, physiological and biochemical parameters at 60 and 75 DAS and yield attributes at harvest (175 DAS). The results showed a parallel increase in most of the parameters with increasing levels of N and P. However, application of 10^?6 mol L^?1 GA₃ in association with N_26.8P_8.94 proved best, it enhanced seed yield, oil yield and fibre yield by 83.3, 97.3 and 78.7%, respectively accompanied with increase in net photosynthetic rate, carbonic anhydrase activity and dry matter accumulation. Among the genotypes tested, Shubhra performed best, while Parvati the least for most of the parameters studied. Thus, combined application of 10^?6 mol L^?1 GA₃ plus N_26.8P_8.94 proved best and can be recommended to exploit the linseed as a dual-purpose crop for good yield of seed and fibre.     

Interactive effects of elevated carbon dioxide and nitrogen availability on fruit quality of cucumber (Cucumis sativus L.)

Elevated CO_2 and high N promote the yield of vegetables interactively, whilst their interactive effects on fruit quality of cucumber(Cucumis sativus L.) are unclear. We studied the effects of three CO_2 concentrations(400 μmol mol–1(ambient), 625 μmol mol–1(moderate) and 1 200 μmol mol–1(high)) and nitrate levels(2 mmol L~(–1)(low), 7 mmol L~(–1)(moderate) and 14 mmol L~(–1)(high)) on fruit quality of cucumber in open top chambers. Compared with ambient CO_2, high CO_2 increased the concentrations of fructose and glucose in fruits and maintained the titratable acidity, resulting in the greater ratio of sugar to acid in moderate N, whilst it had no significant effects on these parameters in high N. Moderate and high CO_2 had no significant effect on starch concentration and decreased dietary fiber concentration by 13 and 18%, nitrate by 31 and 84% and crude protein by 19 and 20% averagely, without interactions with N levels. The decreases in amino acids under high CO_2 were similar, ranging from 10–18%, except for tyrosine(50%). High CO_2 also increased the concentrations of P, K, Ca and Mg but decreased the concentrations of Fe and Zn in low N, whilst high CO_2 maintained the concentrations of P, K, Ca, Mg, Fe, Mn, Cu and Zn in moderate and high N. In conclusion, high CO_2 and moderate N availability can be the best combination for improving the fruit quality of cucumber. The fruit enlargement, carbon transformation and N assimilation are probably the main processes affecting fruit quality under CO_2 enrichment.     

Precision phenotyping of contrasting potato(Solanum tuberosum L.) varieties in a novel aeroponics system for improving nitrogen use efficiency: In search of key traits and genes

With increasing population, degrading soil health, limited arable land area, and high cost of nitrogen(N) fertilizers, improving nitrogen use efficiency(NUE) of potato is an inevitable approach to save the environment and achieve sufficient tuber yields with less N fertilizer supply. Recently, we have developed an aeroponics system to study NUE in potato using genomics, physiology, and breeding approaches. This study aims on precision phenotyping of plants of two distinct potato varieties(Kufri Gaurav, N efficient; Kufri Jyoti, N inefficient) in the novel aeroponics system. Plants were grown in aeroponics under controlled conditions with low N(0.75 mmol L~(-1) NO_3~-) and high N(7.5 mmol L~(–1) NO_3~-) levels. Plant biomass, root traits, total chlorophyll content, and plant N were increased with increasing N supply, whereas higher NUE parameters namely NUE, agronomic NUE(Ag NUE), N uptake efficiency(NUp E), harvest index(HI), and N harvest index(NHI) were observed at low N. An NUE efficient cv. Kufri Gaurav showed higher tuber dry weight, fresh tuber yield, tuber number per plant, early start of tuber harvesting, root traits, stolon traits, NUE parameters, and higher amino acid(aspartic acid and asparagine) content at low N supply. Higher expression of nitrate reductase(NR), nitrite reductase(NIR), and asparagine synthetase(AS) genes was observed in the leaf tissues of Kufri Gaurav at high N. Thus, aeroponics-based precision phenotyping enables identification of NUE efficient genotypes based on key traits and genes involved in improving NUE in potato. Further, this study suggests that the potential of aeroponics can be utilized to investigate N biology in potato under different N regimes.     

猪场厌氧肥水灌溉对设施油麦菜产量及品质的影响

规模化畜禽养殖粪污已成为我国当前最为重要的污染来源,为有效控制畜禽养殖污染开展了猪场肥水设施灌溉田间试验,研究了不同肥水稀释比例灌溉对油麦菜产量和品质的影响。结果表明:试验用猪场肥水与清水进行1∶2稀释灌溉(折算氮素投入量为292 kg·hm-2)能够提高油麦菜存活率、叶片数和株高,且产量比对照施肥处理增加17.67%。与对照处理和其他稀释比例处理相比,该优化模式生产的油麦菜能够维持较高的维生素C含量,显著抑制叶片中的丙二醛(MDA)含量并削减蔬菜植株内硝酸盐含量,油麦菜品质符合《农产品安全质量无公害蔬菜安全要求》(GB 18406.1—2001),且铜锌含量与对照相比不存在显著性差异,但油麦菜可溶性糖含量略有降低。     

氮钾配比对莴笋品质的效应研究

[目的]为生产优质、高产叶菜类蔬菜提供理论依据。[方法]采用盆栽试验,设4个施肥处理,收获后,测定每盆产量和莴笋的硝酸盐、维生素C、氨基酸和可溶性糖含量。[结果]不同施肥处理间莴笋产量有极显著差异,增施氮肥、钾肥莴笋产量增加13.9%~51.0%,以200 mg/kg N和100 mg/kg K处理增加幅度最大(51.0%)。增施氮肥使莴笋的Vc含量降低6.7%~10.1%,氨基酸含量增加24.9%~44.8%,对硝酸盐和可溶性糖的含量作用不一致,而增施钾莴笋硝酸盐含量增加22.7%,氨基酸和可溶性糖的含量分别降低15.2%和19.9%,对Vc的含量影响不大。[结论]从莴笋产量和品质来看,200 mg/kg N和100 mg/kg K处理对莴笋的综合效应最好,为最佳处理。     

Effect of low-nitrogen stress on photosynthesis and chlorophyll fluorescence characteristics of maize cultivars with different low-nitrogen tolerances

Nitrogen(N) is a critical element for plant growth and productivity that influences photosynthesis and chlorophyll fluorescence. We investigated the effect of low-N stress on leaf photosynthesis and chlorophyll fluorescence characteristics of maize cultivars with difference in tolerance to low N levels. The low-N tolerant cultivar ZH311 and low-N sensitive cultivar XY508 were used as the test materials. A field experiment(with three N levels: N0, 0 kg ha–1; N1, 150 kg ha–1; N2, 300 kg ha–1) in Jiyanyang, Sichuan Province, China, and a hydroponic experiment(with two N levels: CK, 4 mmol L–1; LN, 0.04 mmol L–1) in Chengdu, Sichuan Province, China were conducted. Low-N stress significantly decreased chlorophyll content and rapid light response curves of the maximum fluorescence under light(Fm′), fluorescence instable state(Fs), non-photochemical quenching(qN), the maximum efficiency of PSII photochemistry under dark-adaption(Fv/Fm), potential activity of PSII(Fv/Fo), and actual photochemical efficiency of PSII(ΦPSII) of leaves. Further, it increased the chlorophyll(Chl) a/Chl b values and so on. The light compensation point of ZH311 decreased, while that of XY508 increased. The degree of variation of these indices in low-N tolerant cultivars was lower than that in low-N sensitive cultivars, especially at the seedling stage. Maize could increase Chl a/Chl b, apparent quantum yield and light saturation point to adapt to N stress. Compared to low-N sensitive cultivars, low-N tolerant cultivars maintained a higher net photosynthetic rate and electron transport rate to maintain stronger PSII activity, which further promoted the ability to harvest and transfer light. This might be a photosynthetic mechanism by which low-N tolerant cultivar adapt to low-N stress.     

不同磷浓度对土壤理化性质及防风生长和药材品质的影响

【目的】探讨不同磷浓度处理对土壤特性及防风Saposhnikovia divaricata生长状况、色原酮含量的影响,为防风人工栽培的技术策略制定以及防风对低磷胁迫响应机制的研究提供理论依据。【方法】以2年生防风为材料,设置营养液磷（NH₄H₂PO₄）浓度分别为1.0、0.1和0 （无磷） mmol/L,分别在30、60、90 d时测定土壤理化性质及防风生长特性和4种色原酮总含量,分析不同磷浓度处理防风各指标与4种色原酮总含量的关系。【结果】无磷处理下,2年生防风根粗、根生物量在整个处理期间均低于1.0 mmol·L^-1磷处理,根长在90 d时显著高于1.0和0.1 mmol·L^-1磷处理;土壤pH在60 d后表现为1.0 mmol·L^-1磷处理显著高于0.1 mmol·L^-1和无磷处理;土壤有机质含量在整个试验期表现为1.0和0.1 mmol·L^-1磷处理显著低于无磷处理;90 d时,无磷处理的土壤碱解氮含量显...     

Study on Mutant Induction of Gladiolus by in vitro Culture of Petals

Petals of Gladiolus 'Rose Supreme' were used to establish regeneration system. Developmental characteristics of petals were observed. A total of 94 plantlets of petal somaclonal line were marked in Mj ...     

Comparison of phenolic profiles and antioxidant activities in skins and pulps of eleven grape cultivars(Vitis vinifera L.)

Eleven grape cultivars were analysed to explore the variety differences of fresh grape phenolic profiles. The results showed that free phenolics were predominant in grape skins and pulps, and showed the higher antioxidant activities than bound. In 11 cultivars, Muscat Kyoho extracts had the highest total phenolic content in skins(10.525 mg GAE g~(–1) FW) and pulps(1.134 mg GAE g~(–1) FW), and exhibited the highest DPPH radical scavening capacity(EC_(50)=11.7 μg mL~(–1)) and oxygen radical absorbance capacity(ORAC) value(190.57 μmol TE g~(–1) FW) of free phenolic in skin. In addition, the most abundant phenolics in grape skins were found to be flavonoids such as kaempferol in Kyoho skin(541.2 μg g~(–1) FW), rutin, catechin and epicatechin in Muscat Kyoho skin(262.3, 86.3 and 70.0 μg g~(–1) FW, respectively). Furthermore, the principal component analysis showed a strong difference of phenolic profiles with the cultivars, existing forms and distributions. Pearson correlation coefficient analysis showed a significant linear correlation between total phenolic content and antioxidant activity(P0.05). Therefore, both skins and pulps were rich sources of bioactive phenolic compounds, and Muscat Kyoho was the ideal source among all samples.     

外源氨基酸对不结球白菜和生菜品质的影响

收获前叶面喷施氨基酸对不结球白菜和生菜的生长及品质的研究结果表明,不结球白菜的生长基本不受氨基酸的影响;而生菜对氨基酸反应敏感,混合氨基酸(甘氨酸、异亮氨酸、脯氨酸)明显促进生菜的生长。叶面喷施氨基酸明显增加2种蔬菜叶片及叶柄硝酸盐含量;外源氨基酸降低2种蔬菜叶片硝酸还原酶活性,提高叶片全氮含量。不结球白菜叶片可溶性蛋白质含量各处理之间差异不大,叶片游离氨基酸含量增加,达65．82％-84．8l％,可溶性糖含量明显减少;生菜叶片可溶性蛋白质和氨基酸含量显著减少,可溶性糖含量明显提高。     

A 15N-Labeling Study of the Capture of Deep Soil Nitrate from Different Plant Systems

The objective of this study was to determine the efficiency of different plant systems in capturing deep soil nitrate (NO₃⁻) to reduce NO₃⁻ leaching in a field plot experiment using ¹⁵N labelling. The study was conducted on a calcareous alluvial soil on the North China Plains and the plant systems evaluated included alfalfa (Medicago sativa), American black poplar (Populus nigra) and cocksfoot (Dactylis). ¹⁵N-labelled N fertilizer was injected to 90 cm depth to determine the recovery of ¹⁵N by the plants. With conventional water and nutrient management, the total recovery of ¹⁵N-labeled NO₃⁻-N was 23.4% by alfalfa after two consecutive growth years. The recovery was significantly higher than those by American black poplar (12.3%) and cocksfoot (11.4%). The highest proportion of soil residual ¹⁵N from the labeled fertilizer N (%Ndff) was detected around 90 cm soil depth at the time of the 1st year harvest and at 110-130 cm soil depth at time of the 2nd year harvest. Soil %Ndff in 0-80 cm depth was significantly higher in the alfalfa treatment than those in all the other treatments. The soil %Ndff below 100 cm depth was much lower in the alfalfa than those in all the other treatments. These results indicated that ¹⁵N leaching losses in the alfalfa treatment were significantly lower than by those in the black poplar and cocksfoot treatments, due to the higher root density located in nitrate labeling zone of soil profile. In conclusion, alfalfa may be used as a plant to capture deep soil NO₃⁻ left from previous crops to reduce NO₃⁻ leaching in high intensity crop cultivation systems of North China Plain.     

Optimal control of nitrate in lettuce by a hybrid approach: differential evolution and adjustable control weight gradient algorithms

Since high concentration levels of nitrate in lettuce and other leafy vegetables are undesirable, cultivation of lettuce according to specified governmental regulations is currently an important issue. Therefore, methods are sought in order to produce a lettuce crop that allow maximization of the profits of the grower while at the same time insuring the quality of the crops. Using a two-state dynamic lettuce model that predicts the amount of nitrate at harvest time, an optimal control problem with terminal constraints is formulated. The situation considered may be relevant in a plant factory where a fixed head weight should be reached in fixed time while minimizing light input. First, optimal trajectories of light, CO₂ and temperature are calculated using the adjustable control weight (ACW) gradient method. Subsequently, novel, efficient and modified differential evolution (DE) algorithms are used to obtain an approximate solution to the same optimal control problem. While the gradient method yields a more accurate result, the optimum may be local. In order to exploit the salient characteristics of a DE algorithm as a global direct search method, a hybrid-combined approach is proposed. An approximate solution obtained with a DE algorithm is used to initialize the ACW gradient method. Although local minima did not seem to occur in this particular case, the results show the feasibility of this approach.     

潮土设施油麦菜田灌施猪场肥液的适宜模式研究

为有效控制畜禽养殖污水面源污染,通过设施菜田灌施猪场肥液田间试验,研究猪场肥液与清水不同稀释比例(不稀释,1:1,1:2,1:3,1:5)灌施条件下对油麦菜产量及土壤养分淋失的影响。结果表明,两季油麦菜土壤养分淋失特征存在一致性,不稀释猪场厌氧肥液灌施下土壤不同形态的碳、氮、磷淋失总量最高,总碳、总氮、总磷淋失量分别为637.2、242.1、12.2 mg·区^-1和149.6、61.44、1.13 mg·区^-1,是正常施肥处理的1.01~3.54倍。硝态氮为土壤氮淋溶的主要形式,占总氮淋溶量的84%~91%;无机碳淋溶量占总碳淋溶量的85%~90%,适宜浓度的厌氧肥液(1:2)灌施可有效降低土壤碳的淋溶,对土壤碳的固定起到积极作用。猪场肥液与清水1:2稀释灌施能够提高油麦菜存活率,且产量比对照施肥处理增加17.67%和18%,总碳、总氮、总磷淋失量比对照降低49%~56%、5%~44%和20%~34%。从提高油麦菜产量、控制土壤养分淋溶角度综合考虑,猪场厌氧肥液对油麦菜适宜的灌施模式为:肥液与清水1:2稀释灌施。     

Changes of Intramuscular Fat Composition,Lipid Oxidation and Lipase Activity in Biceps femoris and Semimembranosus of Xuanwei Ham During Controlled Salting Stages

Fatty acid composition of neutral lipids （NLs）, phospholipids （PLs） and free fatty acids （FFAs） from intramuscular fat （IMF）, lipid oxidation and lipase activity in muscle Semimembranosus （SM） and msucle Biceps femoris （BF） of dry-cured Xuanwei ham during the 90-d salting stages were analysed. The salt content increased from 0.34 to 3.52%in BF and from 0.10 to 5.42%in SM during the 90 d salting stage, respectively. PLs of IMF in both BF and SM decreased 54.70%（P〈0.001） and 34.64%（P〈0.05）, furthermore, the saturated fatty acids （SFA）, monounsaturated fatty acids （MUFA） and polyunsaturated fatty acids （PUFA） of PLs in both muscles were hydrolysed almost isochronously. FFAs were increased from 0.46 g 100 g-1 lipids to 2.92 g 100 g-1 lipids in BF at the end of salting, which was lower than SM （from 1.29 g 100 g-1 lipids to 9.70 g 100 g-1 lipids）. The activities of acid lipase, neutral lipase and acid phospholipase all remained active in the 90 d. The thiobarbituric acid reactive substances （TBARS） was slowly increased to 1.34 mg kg-1 muscle in BF and to 2.44 mg kg-1 muscle in SM during the salting stage. In conclusion, the controlled salting process prompted the hydrolysis of PLs of IMF notably and increased the lipid oxidation of muscles within some limits.     

头孢菌素C对蔬菜种子萌发的毒理效应

为探究头孢菌素菌渣无害化处置与肥料化利用过程中残留的头孢菌素C对蔬菜生长的毒理效应,通过恒温保湿培养法,采用生菜（Lactuca sativa Linn.var.ramosa Hort.）、油麦菜（Lactuca sativa var.longifoliaf.Lam）、白菜（Brassica pekinensis（Lour.）Rupr.）及油菜（Brassica campestris L.） 4种蔬菜种子为研究对象,以种子发芽率、幼苗的鲜质量、胚轴长、胚根长为毒性敏感指标,研究了7种浓度头孢菌素C溶液胁迫下4种蔬菜毒性的剂量-效应关系,比较了不同蔬菜在头孢菌素C毒害下的生态毒性差异和相对敏感的指标。结果表明：头孢菌素C溶液对4种蔬菜种子毒性敏感指标的影响程度依次为胚根 > 鲜质量 > 胚轴 > 发芽率;头孢菌素C溶液浓度与4种蔬菜胚根生长率呈显著的线性关系（P<0.01）;头孢菌素C对生菜、油麦菜、白菜以及油菜的最大无响应浓度（NOEC）分别为868.10、727.25、796.27 mg·L^-1和629.277 mg·L^-1,4种蔬菜对头孢菌素C的毒性敏感度依次为油菜 > 油麦菜 > 白菜 > 生菜,其中油菜IC₅₀值为1 538.36 mg·L^-1。研究表明,与油麦菜、白菜和生菜相比,油菜更适合作为后续实验的生态毒性指示植物。     

Interaction effect of nitrogen form and planting density on plant growth and nutrient uptake in maize seedlings

High planting density is essential to increasing maize grain yield.However,single plants suffer from insufficient light under high planting density.Ammonium(NH_4~+)assimilation consumes less energy converted from radiation than nitrateIt is hypothesized that a mixed NO_3~–/NH_4~+supply is more important to improving plant growth and population productivity under high vs.low planting density.Maize plants were grown under hydroponic conditions at two planting densities(low density:only).A significant interaction effect was found between planting density and N form on plant biomass.Compared to nitrate only,75/25NO_3~–/NH_4~+increased per-plant biomass by 44%under low density,but by 81%under high density.Treatment with 75/25NO_3~–/NH_4~+increased plant ATP,photosynthetic rate,and carbon amount per plant by 31,7,and 44%under low density,respectively,but by 51,23,and 95%under high density.Accordingly,carbon level per plant under 75/25NO_3~–/NH_4~+was improved,which increased leaf area,specific leaf weight and total root length,especially for high planting density,increased by 57,17 and 63%,respectively.Furthermore,under low density,75/25NO_3~–/NH_4~+increased nitrogen uptake rate,while under high density,75/25NO_3~–/NH_4~+increased nitrogen,phosphorus,copper and iron uptake rates.By increasing energy use efficiency,an optimum NO_3~–/NH_4~+ratio can improve plant growth and nutrient uptake efficiency,especially under high planting density.In summary,an appropriate supply of NH_4~+in addition to nitrate can greatly improve plant growth and promote population productivity of maize under high planting density,and therefore a mixed N form is recommended for high-yielding maize management in the field.     

基于风洞系统的生菜空气动力学研究

针对目前利用计算流体力学软件(Computational fluid dynamics,CFD)进行植物工厂内部气流模拟仅在空载植物工厂中进行,忽略了生菜对气流存在阻碍的问题,采用风洞试验,对生菜冠层空气动力学参数进行研究。利用风洞系统测定了生菜冠层的阻力系数(C_D),并求得在不同叶面积密度(L)的情况下生菜冠层渗透率(K)与动量损失系数(C_f)之间的关系,将生菜栽培板置于风洞试验段中间位置,分别测量风洞试验段竖直方向和水平方向不同测点位置的稳态压力与风速。通过已求得的参数得到CFD建模中建立生菜多孔介质模型需要的粘滞阻力系数与惯性阻力参数。结果表明:1)本试验测得的生菜冠层阻力系数为0.02;2)成熟生菜(L=32.5 m~2/m~3),其渗透率为0.04 m~2,动量损失系数为0.13;3)动量损失系数C_f取值为0.1～1.0,当叶面积密度L为10、20、30 m~2/m~3时,作物冠层渗透率K的取值范围分别为0.25～25.00、0.06～6.25、0.03～2.78 m~2;4)成熟生菜的粘滞阻力系数为25,惯性阻力系数为1.3。