NITRATE/AMMONIUM RATIOS AFFECT RYEGRASS GROWTH AND NITROGEN ACCUMULATION IN A HYDROPONIC SYSTEM

Ryegrass has increasingly been used in constructed wetlands for treatment of eutrophic wastewater. To properly match plant species with the characteristics of wastewater being treated, it is important to know the performance of plant species under different nitrate/ammonium (NO₃ ^?/NH₄ ⁺) ratios. We investigated ryegrass (Lolium perenne L.) dry matter (DM) production and N accumulation under five NO₃ ^?/NH₄ ⁺ ratios (100/0, 75/25, 50/50, 25/75, 0/100) in a hydroponic system. The results showed that ryegrass total DM, shoot DM, root DM and nitrogen (N) accumulation were greater under NO₃ ^?/NH₄ ⁺ ratios of 50/50 and 75/25 than under other NO₃ ^?/NH₄ ⁺ ratios, indicating that ryegrass can be best used in constructed wetlands for treating wastewater with such NO₃ ^?/NH₄ ⁺ ratios to achieve high biomass production and efficient removal of N. On the other hand, for treating wastewater with either NO₃ ^? or NH₄ ⁺ dominate the inorganic N, other plant species that are more adapted to such conditions should be explored.     

不同铵硝配比对弱光下白菜氮素吸收及相关酶的影响

以黑色遮阳网覆盖模仿弱光环境, 使光照强度为自然光的20%左右, 以自然光照为对照, 采用精确控制水培溶液氮素营养, 研究NH₄⁺-N/NO₃^--N 比例分别为0/100、25/75、50/50、75/25、100/0 对弱光下白菜氮代谢及硝酸还原酶和谷氨酰胺合成酶活性的影响。结果表明, 弱光下, 白菜的鲜重及叶片总氮量以NH₄⁺-N/NO₃^--N 比为25/75 时最大, NH₄⁺-N/NO₃^--N 比为100/0 时最低。随弱光处理的进行, 白菜叶片中硝酸还原酶活性及谷氨酰胺合成酶活性均呈下降趋势, 但NH₄⁺-N/NO₃^--N 比为25/75 时, 可维持叶片内较高的硝酸还原酶活性及谷氨酰胺合成酶活性。试验表明, NH₄⁺-N/NO₃^--N 比25/75 是白菜在弱光下生长的较适宜氮素形态配比。     

DEVELOPMENT OF A SOIL N TEST FOR FERTILIZER REQUIREMENTS FOR WHEAT

Optimal fertilizer nitrogen (N) rates result in economic yield levels and reduced pollution. A soil test for determining optimal fertilizer N rates for wheat has not been developed for Quebec, Canada, or many other parts of the world. Therefore, the objectives were to determine: 1) the relationship among soil nitrate (NO^? ₃)- N, soil ammonium (NH ⁺ ₄)- N and N fertilizer on wheat yields; and 2) the soil sampling times and depths most highly correlated with yield response to soil NO^? ₃-N and NH ⁺ ₄-N. In a three year research work, wet and dried soil samples of 0- to 30- and 30- to 60-cm depths from 20 wheat fields that received four rates of N fertilizer at seeding and postseeding (plants 15 cm tall) were analyzed for NH ⁺ ₄-N and NO^? ₃ -N using a quick-test (N-Trak) and a standard laboratory method. Wheat yield response to N fertilizer was limited, but strong to soil NO^? ₃-N.     

Development of a Soil N Test for Fertilizer Requirements for Corn Production in Quebec

Corn requires high nitrogen (N) fertilizer use, but no soil N test for fertilizer N requirement is yet available in Quebec. Objectives of this research were (1) to determine the effects of soil nitrate (NO₃ ^?)-N, soil ammonium (NH₄ ⁺)-N, and N fertilizer rates on corn yields and (2) to determine soil sampling times and depths most highly correlated with yields and fertilizer N response under Quebec conditions. Soil samples were taken from 0- to 30-cm and 30- to 60-cm depths at seeding and postseeding (when corn height reached 20 cm) to determine soil NH₄ ⁺ and NO₃ ^? in 44 continuous corn sites fertilized with four rates of N in two replications using a quick test (N-Trak) and a laboratory method. The N-Trak method overestimated soil NO₃ ^?-N in comparison with the laboratory method. Greater coefficients of determination were observed for soil NO₃ ^?-N analyses at postseeding compared with seeding.     

Effect of Nitrate/Ammonium Ratios on Growth,Root Morphology and Nutrient Elements Uptake of Watermelon (Citrullus Lanatus) Seedlings

Nitrogen is taken up by most plant species in the form of nitrate and ammonium. The objective of this study was to investigate the effect of different nitrogen forms on the growth of watermelon seedlings. Plants were grown in hydroponic culture with five nitrate (NO₃^?)/ammonium (NH₄⁺) ratios (100/0, 75/25, 50/50, 25/75, 0/100). When the proportion of NH₄⁺ was increased, the leaf number, leaf area, shoot height, net photosynthesis, biomass, and root growth were significantly decreased. Higher concentrations of nitrogen (N) and phosphorus (P) were observed when plants were supplied with mixed NO₃^? and NH₄⁺ compared to NO₃^? or NH₄⁺ alone, whereas the concentrations of potassium (K), calcium (Ca), and magnesium (Mg) were decreased with increasing NH₄⁺. The microelements concentrations were generally increased with more NH₄⁺ added. In addition, plants fed with higher NO₃^?/NH₄⁺ ratios resulted in more minerals accumulation.     

Effect of Ammonium:Nitrate Ratios in the Response of Strawberry to Alkalinity in Hydroponics

Strawberry (Fragaria ananasa) plants were grown in hydroponics in a greenhouse, where the supply of different ammonium (NH₄⁺): nitrate (NO₃^?) ratios, was investigated to reduce the negative effect of alkalinity in nutrient solutions. The experiment was arranged in factorial combination with two factors, NH₄⁺:NO₃^? ratios (0%:100%, 25%:75%, 50%:50%, 75%:25%, and 100%:0%) and bicarbonate (0, 25, 50, and 75 mM; NaHCO₃). Plants treated with increasing bicarbonate concentrations exhibited significantly inhibited growth. In plants treated with NH₄⁺ and NO₃^? simultaneously, there was a counteraction of the bicarbonate-induced growth suppression. Sole NO₃^? application in the presence of high bicarbonate resulted in poor growth and plant death due to high alkalinity. The adverse effect of alkalinity on SPAD values and maximal quantum yield of PSII photochemistry (F_v/F_m) alleviated with increasing proportion of NH₄⁺ in nutrient solutions. The results showed that fruit numbers and yield of strawberry increased with elevation of NH₄⁺ in nutrient solutions.     

Effect of Ammonium: Nitrate Ratio on Yield,Calcium Concentration,and Photosynthesis Rate in Strawberry

The effect of ammonium:nitrate (NH₄:NO₃) ratio in nutrient solution on growth, photosynthesis (Pn), yield, and fruit quality attributes in hydroponically grown strawberry (Fragaria × ananassa Duch) cvs. ‘Camarosa’ and ‘Selva’ was evaluated. There were four nutrient solutions of differing NH₄:NO₃ ratios as follows: 0:100, 25:75, 50:50, and 75:25. Plants grown in solution with 75% NH₄ had lower leaf fresh and dry weights and leaf area than those with 25% NH₄ in both cultivars. High ratios of NH₄ and NO₃ in the solution always reduced the yield. The yield was increased by 38% and 84% in ‘Camarosa’ and ‘Selva,’ respectively, when the plants were grown in the 25NH₄:75NO₃ solution compared with plants grown in a higher NH₄ ratio solution. The increased yield at the 25 NH₄:75NO₃ ratio was the result of the increase in fruit size, i.e., length and fresh weight of fruits. Plants grown in the 25NH₄:75NO₃ solution had the highest rate of Pn, while those grown in 75NH₄:25NO₃ solution had the lowest Pn rates in both cultivars. Increasing the NH₄ ratio in the solution from 0 to 75% significantly reduced the calcium (Ca) concentration and postharvest life of the fruits in both cultivars. Both higher leaf area and Pn rate appeared to be the reason for the increased yield and plant growth in the 25:75 ratios of nitrogen (N). The results indicate the preference of strawberry plant growth toward a greater nitrate N form in a hydroponic solution. Therefore, a combination of two forms of N in an appropriate ratio (25NH₄:75NO₃) appears to be beneficial to plant growth, yield, and quality of strawberry fruits.     

Influence of nitrogen forms and levels on the growth and nutrition of cacao

Ammonium and nitrate are the major forms of nitrogen (N) present in tropical soils. An experiment was conducted to assess the influence of nitrate and ammonium forms (NO₃^?, NH₄⁺, and mix of NO₃^? + NH₄⁺), and levels (1.5–12.0 mM) of N on the growth and nutrition of cacao (Theobroma cacao L). Growth parameters were significantly influenced by N forms, and nitrogen supplied as NH₄⁺ proved better for the growth of cacao compared with NO₃^? form and mixtures of these two forms. Irrespective of the forms of N, levels of N had no significant effect on plant growth parameters. Nutrient efficiency ratios (NERs) (shoot dry matter produced per unit of nutrient uptake) for macronutrients were sulfur>phosphorus>calcium>magnesium>nitrogen>potassium (S>P>Ca>Mg>N>K) and for micronutrients NERs were in the order of copper>boron>zinc>iron>manganese (Cu>B>Zn>Fe>Mn).     

Effects of Nitrogen Levels and Nitrate/Ammonium Ratios on Oxalate Concentrations of Different Forms in Edible Parts of Spinach

Two hydroponic experiments were carried out to investigate the effects of nitrogen (N) levels and forms on the oxalate concentrations of different form in edible parts of spinach. Nitrogen was supplied at five levels (4, 8, 12, 16, 20 mM) in Experiment 1 and five ratios of nitrate (NO₃ ^?) to ammonium (NH₄ ⁺) (100/0, 75/25, 50/50, 25/75, 0/100) at a total N of 8 mM in Experiment 2. Biomass of spinach increased markedly from 4 mM to 8 mM N and reached the flat with further increase in N. The total oxalate and soluble oxalate in leaves and shoots (edible parts) increased significantly with increasing N levels from 4 to 12 mM, while the total oxalate and insoluble oxalate decreased markedly when N level was further increased from 12 to 20 mM. Oxalates of different forms in petioles increased first and then decreased and elevated again with increasing nitrogen levels. In the second experiment, decreasing NO₃ ^?/NH₄ ⁺ ratios markedly increased at first and then significantly decreased the biomass of spinach plants and the maximum biomass was recorded in the treatment of the NO₃ ^?/NH₄ ⁺ ratio of 50:50. The oxalate concentrations of different form in leaves and shoots were all decreased obviously as the ratio of NO₃ ^?/NH₄ ⁺ decreased from 100:0 to 0:100. Concentrations of total oxalate and soluble oxalate in petioles could be reduced by increasing ammonium proportion and were the lowest as the ratio of NO₃ ^?/NH₄ ⁺ was 50:50 and insoluble oxalate decreased as nitrate/ammonium ratio decreased. The concentrations of oxalate forms in leaves were all higher than those in petioles and soluble oxalate was predominant form of oxalates in both trials. It is evident that high biomass of spinach can be achieved and oxalate concentrations of different forms can be reduced by modulating N levels and NO₃ ^?/NH₄ ⁺ ratio, so this will benefit for human health especially for those people with a history of calcium oxalate kidney stones.     

Soil inorganic nitrogen composition and plant functional type determine forage crops nitrogen uptake preference in the temperate cultivated grassland,Inner Mongolia

ABSTRACT

Plant nitrogen (N)-acquisition strategy affects soil N availability, community structure, and vegetation productivity. Cultivated grasslands are widely established to improve degraded pastures, but little information is available to evaluate the link between N uptake preference and forage crop biomass. Here an in-situ ¹⁵N labeling experiment was conducted in the four cultivated grasslands of Inner Mongolia, including two dicots (Medicago sativa and Brassica campestris) and two monocots (Bromus inermis and Leymus chinensis). Plant N uptake rate, shoot- and root biomass, and concentrations of soil inorganic-N and microbial biomass-N were measured. The results showed that the root/shoot ratios of the dicots were 2.6 to 16.4 fold those of the monocots. The shoot N concentrations of the dicots or legumes were 40.6% to 165% higher than those of the monocots or non-legumes. The four forage crops in the cultivated grassland preferred to uptake more NO₃^?-N than NH₄⁺-N regardless of growth stages, and the NH₄⁺/NO₃^? uptake ratios were significantly lower in the non-legumes than in the legumes (p < 0.05). Significant differences in the NH₄⁺-N rather than NO₃^?-N uptake rate were observed among the four forages, related to plant functional types and growth stages. The NH₄⁺ uptake rate in the perennial forages exponentially decreased with the increases in shoot-, root biomass, and root/shoot ratio. Also, the plant NH₄⁺/NO₃^? uptake ratio was positively correlated with soil NH₄⁺/NO₃^? ratio. Our results suggest that the major forage crops prefer to absorb soil NO₃^?-N, depending on soil inorganic N composition and belowground C allocation. The preferential uptake of NO₃^?-N by forages indicates that nitrate-N fertilizer could have a higher promotion on productivity than ammonium-N fertilizer in the semi-arid cultivated grassland.     

氮肥形态及配比对菠菜生长和安全品质的影响

【目的】铵态氮肥和硝态氮肥是蔬菜生长过程中经常施用的氮肥种类,氮肥形态及配比对蔬菜生长和安全品质有着重要影响。菠菜是一种叶菜类蔬菜,富含矿质元素、维生素C和维生素E。本文通过施用铵态氮和硝态氮肥,探究氮肥形态及其配比(NH+4-N/NO-3-N)对菠菜生长和安全品质的影响。【方法】采用水培试验,设置5种不同氮素形态配比(NH+4-N/NO-3-N比值分别为100∶0、75∶25、50∶50、25∶75和0∶100)的营养液,定期采集菠菜样品并测定菠菜的生物量、株高、根系长度、硝酸盐和亚硝酸盐、有机酸和氨基酸参数值。【结果】随着NH+4-N/NO-3-N比值从100∶0变化到0∶100,菠菜的生物量、株高、根系长度、硝酸盐和亚硝酸盐累积量以及有机酸含量均呈增加趋势,而氨基酸总量则明显下降;当NH+4-N/NO-3-N比值为0∶100时,菠菜茎叶生物量为6.2g/plant,株高和根系长度分别为16.3 cm和22.5 cm,分别是NH+4-N/NO-3-N比值为100∶0时的6倍、2.2倍和2.0倍,表明菠菜是一种喜硝酸盐氮的蔬菜;当NH+4-N/NO-3-N比值由0∶100变为25∶75时,即在氮肥组合中增加25%的铵态氮肥,此时的硝酸盐和亚硝酸盐含量分别由398.5 mg/kg、1.42 mg/kg降为249.1 mg/kg、0.98mg/kg,降幅为37.5%和8.0%,表明在菠菜生长过程中适当增施铵态氮肥可有效降低硝酸盐和亚硝酸盐在茎叶中的累积;当NH+4-N/NO-3-N比值从100∶0变化到0∶100,对6种有机酸(苹果酸、富马酸、琥珀酸、α-酮戊二酸、柠檬酸和丙酮酸)而言,增加幅度最大的是富马酸,约8.6倍,增加幅度最小的是柠檬酸,约2.5倍,苹果酸则在NH+4-N/NO-3-N=25∶75时达到最大值,为985.3 mg/L;随着NH+4-N比例的减少,菠菜茎叶中的氨基酸总量呈下降趋势,NH+4-N/NO-3-N比值为100∶0、75∶25、50∶50、25∶75和0∶100的氨基酸总量分别为21.80μmol/g、12.92μmol/g、9.20μmol/g、8.30μmol/g和7.50μmol/g,表明菠菜的营养价值降低,这一趋势与上述所研究的指标(株高、根系长度、硝酸盐和亚硝酸盐含量以及有机酸含量)有着明显的区别。【结论】菠菜是一种典型的喜硝态氮类蔬菜,施用硝态氮肥可明显提高菠菜产量,但过高的施用量可导致菠菜安全品质下降。适当增施铵态氮肥可降低硝酸盐和亚硝酸盐在菠菜体内的累积,并有效调节氨基酸和有机酸的代谢。因此,在菠菜种植过程,应该合理地搭配铵态氮肥和硝态氮肥,以便在保证安全性和营养价值的基础上获取最大的生物量。     

Nitrogen partitioning in greenhouse‐grown broccoli in response to varying NH+ 4:NO− 3 ratios

Abstract

Broccoli (Brassica oleracea var. italica) plants were grown in the greenhouse and supplied continuously with 18 mM N in the following NH⁺ ₄:NO^? ₃ ratios: 100:0, 75:25, 50:50, 25:75, 0:100. At commercial maturity, the plant characteristics and partitioning of nitrogen in xylem and phloem saps and in plant tissue were determined. Plants fed solely with NH⁺ ₄ were stunted, exhibited signs of marginal necrosis on the lower leaves, and accumulated NH⁺ ₄ in the foliage. The maximum yield and shortest harvest time, together with minimal NO^? ₃ and NH⁺ ₄ accumulation were found at a ratio of 75:25. Ammonium concentrations in xylem sap decreased linearly with decreasing NH⁺ ₄ portion in the nutrient solution, whereas the NO^? ₃ concentrations reached a maximum when NO^? ₃ constituted 50% of the N supply. The glutamate family dominated the amino acid composition of both xylem and phloem saps, but did not vary much with NH⁺ ₄:NO^? ₃ ratio. It is suggested that the NH⁺ ₄ concentration in xylem sap may be used to assess NH⁺ ₄ vs NO^? ₃ utilization by broccoli grown under field conditions.     

Effect of Inorganic N Composition of Fertilizers on Nitrous Oxide Emission Associated with Nitrification and Denitrification

We studied the effect of repeated application (once every 2 d) of a fertilizer solution with different ratios of NH₄ ⁺ - and NO₃ ^?-N on N₂O emission from soil. After the excess fertilizer solution was drained from soil, the water content of soil was adjusted to 50% of the maximum water-holding capacity by suction at 6 × 10³ Pa. Repeated application of NH₄ ⁺- rich fertilizer solution stimulated nitrification in soil more than NO₃ ^?-rich fertilizer. Although the evolution of N₂O through nitrifier denitrification tended to increase with the repeated addition of a fertilizer solution rich in NH₄ ⁺ rather than in NO₃ ^?, the contribution of nitrifier denitrification remained at levels of 20 to 36% of the total emission regardless of the inorganic N composition. The total emission of N₂O also tended to increase with the application of NH₄ ⁺- rather than NO₃ ^?-rich fertilizer. It was suggested that the coupled process of nitrification and denitrification at micro-aerobic sites became important when fertilizer rich in NH₄ ⁺ was applied to soil under relatively aerobic conditions.     

聚天门冬氨酸钙盐对水稻田面水中三氮动态变化的影响

利用桶栽试验探究不同浓度水平的聚天门冬氨酸钙盐(PASP-Ca)对水稻田面水中铵态氮(NH_4~+)、硝态氮(NO_3~-)和总氮(TN)浓度动态变化的影响。结果表明,施氮后,田面水中TN、NH_4~+和NO_3~-分别于第1,3,9天达到最大值,随后逐渐降低。NO_3~-/TN多在0.1以下,(NH_4~++NO_3~-)/TN多在0.5以上。因此,可以将NH_4~+和TN作为农田水污染防治的主要监测指标,NO_3~-作为辅助指标。添加一定浓度的PASP—Ca能对田面水中氮素浓度的变化起到缓释作用,其中0.3%浓度水平的PASP—Ca效果相对较好,田面水中NH_4~+和TN的下降速率分别为3.452,4.806mg/(L·d),与单施氮肥(CK)相比,分别降低了11.68%和16.25%;同时,NH_4~+的平均浓度为6.999mg/L,较CK低了3.88%;NO_3~-的平均浓度为0.396mg/L,较CK低了24.83%;TN的平均浓度为20.077mg/L,较CK提升了3.10%。施氮后田面水中TN浓度随时间呈对数递减,而NH_4~+浓度在施氮后3天内随时间呈对数增加,之后随时间呈对数递减趋势。施氮后的9天内是防止稻田田面水中氮素流失的关键时期。     

Root Carbon Enrichment Alleviates Ammonium Toxicity in Cucumber Plants

ABSTRACT

The addition of carbonates to a nutrient solution to alleviate ammonium (NH₄ ⁺) toxicity in hydroponically-grown cucumber (Cucumis sativus L.) plants was investigated. Stable isotopes [nitrogen (¹⁵N) and carbon (¹³C)] were used to assess the uptake of nitrogen [NH₄ ⁺ or nitrate (NO₃ ^?)] as well as carbon [bicarbonate (HCO₃ ^?)/carbonate (CO₃ ^2?)] by the roots. Ammonium as the sole N source at 5 mM decreased plant fresh weights compared to NO₃ ^?. However, at lower concentrations of NH₄ ⁺ (25% of 5 mM total N), growth was increased compared to NO₃ ^? alone. Inorganic C enrichment [calcium carbonate (CaCO₃)] of the nutrient solution increased the fresh weight of NH₄ ⁺ grown plants with up to 150% relative to control plants receiving calcium hydroxide [Ca(OH)₂] for pH regulation. Root ¹⁵N enrichment was lower in ¹⁵NH₄ ⁺ supplied plants compared to ¹⁵NO₃ ^?, while the ¹³C enrichment in leaves was increased by NH₄ ⁺ nutrition compared to NO₃ ^? or NH₄NO_3. The enhanced C capture was associated with high PEPCase activity in the roots. It is concluded that inorganic carbon enrichment of the root medium may alleviate NH₄ ⁺ toxicity via increased synthesis of C skeletons and, accordingly, increased capacity for NH₄ ⁺ assimilation and N export to the shoots.     

减氮配施有机物质对土壤氮素淋失的调控作用

采用室内土柱模拟试验方法,研究不同氮肥施用下1m土体中氮素的分布和移动特征,揭示土壤氮素动态变化规律。结果表明:FN(农民习惯施无机氮用量)、RN(根据土壤养分供应和作物需求确定的推荐无机氮用量)显著增加了土壤上层NH_4^+-N和NO_3^--N向下层淋失。RN+HA(与推荐无机氮纯养分相等的锌腐酸尿素)和RN40%+OMB(推荐无机氮肥减60%基础上配施自制有机调理物质)可延长上层土壤NH_4^+-N峰值出现时间,降低下层NH_4^+-N。淋溶结束后,等氮量下增施HA较RN降低60cm以下NH_4^+-N残留29.7%～54.2%;降低60—80cm NO_3^--N累积17.4%。RN40%+OMB处理无机氮肥用量最小,0—20cm的NH_4^+-N最高,40—100cm稳定在2.0mg/kg左右;0—20,20—40cm土层NO_3^--N较RN+HA增加12.3%和2.0%,显著降低40cm以下NO_3^--N残留。RN+HA和RN40%+OMB较RN的土壤总无机氮残留分别减少7.4%和20.2%,降低表观淋失率。因此,RN40%+OMB可较好地抑制氮素下移,降低氮素淋失风险,为减少氮素淋失、明确合理氮肥施用方式提供科学依据。     

Growth,Nitrate Accumulation,and Macronutrient Concentration of Pakchoi as Affected By External Nitrate-N: Amino Acid-N Ratio

ABSTRACT

A study was carried out to determine the influence of nitrogen (N) sources on the growth, nitrate (NO₃ ^?) accumulation, and macronutrient concentrations of pakchoi (Brassica chinensis L.) in hydroponics. Plants were supplied with NO₃ ^? and two amino acids (AA), glutamic acid (Glu), and glutamine (Gln), at six NO₃ ^?-N/AA-N molar ratios: (1) 100:0, (2) 80:20, (3) 60:40, (4) 40:60, (5) 20:80, (6) 0:100. The total N concentration was 12.5 mmol/L for all treatments in nutrient solutions. Both AAs reduced plant growth with decreasing NO₃ ^?-N/AA-N ratios, but the reduction was for Gln than for Glu. At 80:20 NO₃ ^?-N: Gln-N ratio, the Gln had no significant effect on pakchoi fresh weights. Decreasing NO₃ ^?-N/AA-N ratios reduced NO₃ ^? concentrations in the plant, regardless of AA sources. Adding an appropriate portion of AA-N to nutrient solutions for hydroponic culture increased concentrations of N, phosphorus (P), and potassium (K) in pakchoi shoots. Substituting 20% or less of NO₃ ^?-N with Gln-N in hydroponic culture will increase the pakchoi quality by reducing NO₃ ^? concentration and increasing mineral nutrient concentrations in shoots without significant reduction of crop yields.     

氮素不同形态配比对菜用大豆生长、种子抗氧化酶活性及活性氧代谢的影响

通过蛭石盆栽试验,研究了氮素不同形态配比对菜用大豆[Glycine max (L.) Merr.]品种"理想95-1"生长、种子抗氧化酶活性及活性氧代谢的影响。结果表明,营养液中适宜的硝铵比(75∶25)有利于菜用大豆的生长发育,植株具有最大生物量;在高比例的硝态氮(100%)和铵态氮(75%)处理下,植株的干重、鲜重及产量均显著降低,以硝铵比为25∶75处理下尤为显著。在适宜的硝铵比(75∶25和50∶50)处理下,菜用大豆种子具有较低的抗氧化酶活性,活性氧代谢产物O2、过氧化氢(H2O2)和膜脂过氧化产物丙二醛(MDA)含量也较低,表明植株受到的氧化胁迫程度较低;而在硝铵比为25∶75处理中,抗氧化酶活性最高,O2生成速率、H2O2和MDA含量也最高,表明过多的铵态氮对细胞膜造成了伤害,所受的氧化损伤程度较重。     

Effect of nitrate/ammonium ratio on biomass production,nitrogen accumulation,and use efficiency in sorghums of different origin

Plant nitrogen (N) uptake, growth, and N use efficiency may be affected by N form (NO₃ ^‐or NH₄ ⁺) available to the root. The objectives of this study were to determine the effect of mixed N form on dry matter production and partitioning, N uptake, and biomass N use efficiency defined as total dry matter produced per unit plant N (NUE₁) in U.S. and tropical grain sorghums [Sorghum bicolor (L.) Moench]. The U.S. derived genotype CK 60 and three tropical genotypes, Malisor‐7, M 35–1, and S 34, were evaluated in a greenhouse trial using three nutrient solutions differing in their NO₃ ^‐/NH₄ ⁺ ratio (100/0, 75/25, 50/50). Shoot and root biomass, N accumulation, and NUE, were determined at 10‐leaf and boot stages. Averaged over all genotypes, shoot and root biomass decreased when NH₄ ⁺ concentration was increased in the solution. Shoot biomass was reduced by 11% for 75/25 and 26% for 50/50 ratios, as compared to 100/0 NO₃ ^‐/NH₄ ⁺. Similarly, root biomass reduction was about 34% and 45% for the same ratios, respectively. Increasing NH₄ ⁺ concentration also altered biomass partitioning between shoot and root as indicated by decreasing root/shoot ratio. Total plant N content and NUE₁ were also reduced by mixed N source. Marked genotypic variability was found for tolerance to higher rates of NH₄ ⁺. The tropical line M 35–1 was well adapted to either NO₃ ^‐ as a sole source, or to an N source containing high amounts of NH₄ ⁺. Such a characteristic may exist in some exotic lines and may be used to improve genotypes which do not do well in excessively wet soil conditions where N uptake can be reduced.     

Changes in plant growth substances,contents and flower quality of rose cv. ‘Dolce Vita’ in response to nitrogen sources under soilless culture conditions

The aim of this study was to investigate the biochemical responses and vase life of rose cut flowers under different ratios of NO₃:NH₄:urea in soilless culture. In this study, urea was used as the source of nitrogen (N) in solution cultures. For this purpose, an experiment was conducted as completely randomized design with seven ratios of N forms and three replications. The rooted cuttings of rose cv Dolce Vita were supplied with seven different ratios of NO₃^?:NH₄⁺:urea (100:0:0, 70:15:15, 50:25:25, 50:0:50, 0:0:100, 50:50:0 and 0:100:0). Results showed that with the increase in urea and ammonium concentrations, the amounts of cuttings IAA, GA₃, zeatin, ABA and polyamines contents decreased significantly. Plants fertigated with nutrient solution containing NO₃^?:NH₄⁺:urea (50:25:25) had the highest concentrations of growth regulators, the highest stalk length and flower vase life. As the ammonium ratios in the nutrient solution increased, the flower vase life decreased significantly. It was concluded that using NO₃^?:NH₄⁺:urea at the ratio of 50:25:25 had the highest effects on improving the rose cut flowers quality by affecting plants growth regulators and can be recommended for cut rose production in soilless culture systems.