Response of Kentucky bluegrass turf to fertilizers containing dicyandiamide

Abstract

Nitrogen fertilization is of major importance in maintaining turfgrass stands. Although rates and sources of N may vary on different turfgrass areas, efficient utilization of N applications is always important. This research was conducted in the field to determine the value of dicyandiamide (DCD) as a nitrification inhibitor and as a slow‐release N source in turfgrass fertilization. The inhibitory effect was studied by applying ammonium sulfate (AS), urea, and a complete fertilizer alone and with 10 and/or 15% of the N replaced with DCD‐N to stands of Kentucky bluegrass. Single and split rates totaling up to 196 kgN/ha/yr were used. Soil NO₃‐N and NH₄‐N analyses sometimes indicated decreased nitrification; however, turfgrass yield and color were essentially unaffected by these rates of DCD. To assess the slow‐release effect of DCD, various ratios of AS‐N or urea‐N to DCD‐N were used to fertilize turf in two experiments. Initial response decreased as the proportion of DCD‐N increased, and in one experiment, a residual effect was noted a year after application when DCD comprised 80 or 100% of the N. Severe, but short‐lived, phytotoxicity from DCD was noted in the other experiment when more than 40% of the N was from DCD. Under the conditions of this research, DCD appeared to have little value in increasing the efficiency of N fertilization.     

Melamine/urea and oxamide fertilization of Kentucky bluegrass

Abstract

The commercial lawn care industry represents a large market for N sources. A formulated melamine (2,4,6‐triamino‐s‐triazine) plus urea combination (MLU) (45% melamine by weight) and oxamide were evaluated for use by the lawn care industry by comparing turfgrass response from these fertilizers to that from urea, sulfur coated urea (SCU), ureaformaldehyde (Nitroform), and a non‐fertilized check. Fertilizers were applied four times per year to field plots of Kentucky bluegrass (Poa pratensis L.) growing on a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll) at a rate of 49 kg N ha^‐1 per application. Color ratings and clipping weights were determined weekly during the growing season. Trends in color ratings paralleled those in clipping weights. During the first year of the study, MLU treated turf received significantly higher color ratings than nonfertilized turf on only 38% of the rating dates; this increased to 76% in the third year of the study. Color ratings for MLU fertilized turf compared more closely to ratings for Nitroform fertilized turf than for ratings for urea or SCU fertilized turf. The turf fertilized with oxamide received higher color ratings than Nitroform or urea fertilized turf and compared favorably with SCU fertilized turf. Programs utilizing MLU would require either high initial application rates or supplemental applications of another N source to provide acceptable results. Oxamide appeared suitable for use by the lawn care industry.     

叶面喷施有机硅对草地早熟禾幼苗生长的影响

为明确有机硅对草地早熟禾幼苗生长的影响,以草地早熟禾(Poa pratensis L.)品种"午夜"为参试材料,设置7个有机硅肥梯度(0、1、2、2.5、3、4、5 mmol·L~(-1))进行叶面喷施,研究了不同浓度的有机硅对草地早熟禾苗长、苗干重、根长、根干重、根系总长、根系总表面积、根头数、叶片相对电导率及地上部硅含量的影响。结果表明,添加一定浓度的有机硅可以增加草地早熟禾的苗长、苗干重、根长、根干重、根系总长、根系总表面积和根头数,其中施有机硅2.5 mmol·L~(-1)处理表现最佳,显著高于对照,对根系平均直径有促进作用,但不显著;干旱胁迫下喷施有机硅能够减少叶片细胞电解质的渗漏,保持叶片细胞膜的完整性,提高草地早熟禾抗逆性;喷施不同浓度的有机硅均能显著提高草地早熟禾地上部含硅量,其中喷施3 mmol·L~(-1)有机硅制剂含硅量最高。可见,适宜浓度的有机硅显著促进了草地早熟禾的生长。     

Responses of Kentucky bluegrass cultivars to excess aluminum in nutrient solutions

Kentucky bluegrass, Poa pratensis L., is generally regarded as an acid‐soil‐sensitive species. However, previous studies in our laboratory showed that cultivars within the species differed widely in tolerance to acid Tatum subsoil (pH 4.6) which is used routinely to screen plants for aluminum (Al) tolerance. In the early studies, specific differential Al tolerance was not demonstrated. The objective of the current study was to test the hypothesis of differential Al tolerance more precisely in nutrient solutions. In one experiment, acid‐soil‐tolerant Victa and Fylking and acid‐soil‐sensitive Windsor and Kenblue cultivars were grown for 35 days in nutrient solutions containing 0, 2, 4, 6, 12, and 24 mg Al L^‐1, at initial pH 4.5, with no subsequent adjustment. In a second experiment, Victa and Windsor were grown for 30 days in solutions containing 0, 4, and 6 mg Al L^‐1, at initial pH 4.5, with no further adjustment. For Victa and Windsor, tolerance to Al in nutrient solution corresponded with tolerance to acid Tatum subsoil, however, the cultivar difference in tolerance, based on relative root dry weight, was only about 2‐fold, compared with 20‐fold in acid Tatum subsoil. Fylking and Kenblue cultivars, which showed a wide difference in tolerance to acid Tatum subsoil, did not show distinct differences in tolerance to Al in nutrient solutions. Possible reasons for this discrepancy are discussed. Superior Al tolerance of Victa (compared with Windsor) was associated with a greater plant‐induced increase in the pH of its nutrient solutions and a corresponding decrease in concentrations of soluble Al in the filtered solutions at the end of the experiments. Greater Al sensitivity in Windsor (compared with Victa) was not related to reduced uptake of phosphorus (P) or excessive uptake of Al; neither cultivar accumulated appreciable Al concentrations in its shoots. The observed differential acid soil and Al tolerance among bluegrass cultivars appears worthy of further study. Improved understanding of Al tolerance mechanisms would contribute to fundamental knowledge of plant mineral nutrition and could aid plant breeders in tailoring plants for greater tolerance to acid subsoils.     

返青前后草地早熟禾草坪根际微生物区系动态

根际是土壤-植物生态系统物质及能量交换的活跃界面,根际微生物不仅直接影响植物对水分、养分的吸收,而且也同时影响植物对不良环境的抵抗能力。利用选择性培养基对草地早熟禾（PoapratensisL.）返青前后根际与非根际的细菌、真菌以及放线菌类群进行分离测数,拟从根际及非根际土壤微生物区系动态变化方面来阐述草地早熟禾返青前后其根际微生态的变化规律。结果表明：（1）草地早熟禾草坪的返青后,根际及非根际细菌、真菌数量明显增加,但放线菌数量呈减少趋势;（2）无论返青前后或者根际以及非根际,细菌的数量都占整个土壤微生物量的绝大部分,细菌数量的变化代表了整个微生物类群数量的变化趋势,使得草地早熟禾返青后根际土壤由“真菌型”向“细菌型”转化;（3）返青前后,各微生物类群都表现出明显的根际效应。     

Role of Azospirillum brasilense nitrate reductase in nitrate assimilation by wheat plants

Summary The nitrogen metabolism of wheat plants inoculated with various Azospirillum brasilense strains and nitrate reductase negative (NR^–) mutants was studied in two monoxenic test tube experiments. The spontaneous mutants selected with chlorate under anaerobic conditions with nitrite as terminal electron acceptor fixed N₂ in the presence of 10 mM NO₃ ^– and were stable after the plant passage. One strain (Sp 245) isolated from surface-sterilized wheat roots produced significant increases in plant weight at both NO₃ levels (1 and 10 mM) which were not observed with the NR^– mutants or with the two other strains. Similar effects were observed in a pot experiment with soil on dry weight and total N incorporation but only at the higher N fertilizer level. In the monoxenic test tube experiments plants inoculated with the mutants showed lower nitrogenase activities than NR⁺ strains at the low NO₃ ^– level (1 = mM) but maintained the same level of activity with 10 mM NO₃ ^– where the activity of all NR⁺ strains was completely repressed. The nitrate reductase activity of roots increased with the inoculation of the homologous strains and with the mutants at both NO₃ ^– levels. At the low NO₃ ^– level this also resulted in increased activity in the shoots, but at the high NO₃ ^– level the two homologous strains produced significantly lower nitrate reductase activity in shoots while the mutants more than doubled it. The possible role of the bacterial nitrate reductase in NO₃ ^– assimilation by the wheat plant is discussed.     

Evaluation of N,P, S and B fertilization of Kentucky bluegrass seed in northern Idaho

Abstract

Current nitrogen (N) fertilizer recommendations for Kentucky bluegrass (Poa pratensis L.) seed production in northern Idaho are based on potential yield and annual precipitation. Soil test correlation information collected for other northern Idaho crops provide the basis for P, S and B recommendations. The objective of this paper is to assess the current recommendations with a series of forty field trials conducted on ten sites during four seed production seasons. All field trials were conducted on Alfisols and Mollisols initially containing less than 60 kg N/ha, 3.5 μg/g NaOAc extractable P, 40 kg extractable SO₄‐S/ha and 0.5 μg/g extractable B. Fertilization rates evaluated included: 0, 50, 75, 100, 125, 150 and 200 kg N/ha; 0, 30 and 60 kg P₂O₅/ha; 0, 25, and 50 kg SO₄‐S/ha, and 0 and 1.5 kg B/ha. Five field sites contained the cultivar ‘Argyle’ Kentucky bluegrass seed, while the other five sites contained the cultivar ‘South Dakota’.

Excellent relationships between percent maximum Kentucky bluegrass seed production and the sum of inorganic soil N + fertilizer N applied were observed for the ‘Argyle’ (R²=0.65) and ‘South Dakota’ (R²=0.72) cultivars. Phosphorus applications of 30 kg P₂O₅/ha improved seed yields from 10.0 to 51.6% when initial soil test values were less than 3.0 6 μg/g NaOAc extractable P. When initial SO₄‐S soil values were less than 32 kg/ha fertilizer additions increased seed yields from 12.6 to 107.3%. Boron applications did not improve seed yields. Analysis of these trials indicates that adequate information is available to make satisfactory P, S and B fertilizer recommendations; however, additional soil test correlation information is needed for N recommendations.     

Potential importance of bacteria and fungi in nitrate assimilation in soil

Soil microorganisms can use a wide range of N compounds but are thought to prefer NH₄⁺. Nevertheless, ¹⁵N isotope dilution studies have shown that microbial immobilization of NO₃⁻ can be an important process in many soils, particularly relatively undisturbed soils. Our objective was to develop a method for measuring NO₃⁻ immobilization potential so that the relative contributions of bacteria and fungi could be determined. We modified and optimized a soil slurry method that included amendments of KNO₃, glucose, and methionine sulfoximine (an inhibitor of N assimilation) in the presence of two protein synthesis inhibitors: chloramphenicol, which inhibits bacteria, or cycloheximide, which inhibits fungi. By adding ¹⁵N-labeled KNO₃, we were able to measure gross rates of NO₃⁻ production (i.e., gross nitrification) and consumption (i.e., gross NO₃⁻ immobilization). We found that bacteria, not fungi, had the greatest potential for assimilating, or immobilizing, NO₃⁻ in these soils. This is consistent with their growth habit and distribution in the heterogeneous soil matrix.     

Diurnal variation of nitrate concentration in cereals grown under rainfed mediterranean conditions

Abstract

Standardization of sampling methodology is essential when using plant analysis as an indicator of the nutrition status of a crop. Time of sampling during the day is a factor which was shown to affect tissue nitrate (NO₃) concentration of irrigated crops. The diurnal variation of NO₃ concentration in small grain cereal plants, grown under rainfed mediterranean conditions, was tested by an in situ sap test and by analysing dried tissue. Variation in NO₃ concentration was shown to exist among plants grown under field conditions. Variation was also shown to exist at different hours of sampling within the day. However, these variations did not follow any diurnal trend and the magnitude of the difference in NO₃ concentration did not affect the diagnosis of the nitrogen (N) nutrition status of the crop. The results suggest that diurnal variation of NO₃ concentration of cereals grown under rainfed Mediterranean conditions is not a major concern in using NO₃ tissue tests to predict N availability provided that sampling is done during the daylight hours.     

Simulated glyphosate drift influences nitrate assimilation and nitrogen fixation in non-glyphosate-resistant soybean

Nontarget injury from glyphosate drift is a concern among growers using non-glyphosate-resistant (non-GR) cultivars. The effects of glyphosate drift on nitrate assimilation and nitrogen fixation potential, nodule mass, and yield of non-GR soybean were assessed in a field trial at Stoneville, MS. A non-GR soybean cultivar 'Delta Pine 4748S' was treated with glyphosate at 12.5% of use rate of 0.84 kg of active ingredient/ha at 3 (V2), 6 (V7), and 8 (R2, full bloom) weeks after planting (WAP) soybean to simulate glyphosate drift. Untreated soybean was used as a control. Soybeans were sampled weekly for 2 weeks after each glyphosate treatment to assess nitrate assimilation and N2 fixation potential. Nitrate assimilation was assessed using in vivo nitrate reductase assay in leaves, stems, roots, and nodules. Nitrogen fixation potential was assessed by measuring nitrogenase activity using the acetylene reduction assay (ARA). Nitrogen content of leaves, shoots, and seed and soybean yield were also determined. In the first sampling date (4 WAP), glyphosate drift caused a significant decrease in NRA in leaves (60%), stems (77%), and nodules (50%), with no decrease in roots. At later growth stages, NRA in leaves was more sensitive to glyphosate drift than stems and roots. Nitrogenase activity was reduced 36-58% by glyphosate treatment at 3 or 6 WAP. However, glyphosate treatment at 8 WAP had no effect on nitrogenase activity. Nitrogen content was affected by glyphosate application only in shoots after the first application. No yield, seed nitrogen, protein, or oil concentration differences were detected. These results suggest that nitrate assimilation and nitrogen fixation potential were significantly reduced by glyphosate drift, with the greatest sensitivity early in vegetative growth. Soybean has the ability to recover from the physiological stress caused by glyphosate drift.     

氮素亏缺对苹果愈伤组织硝态氮吸收及同化的影响

【目的】研究硝态氮亏缺对苹果叶片愈伤组织生长及硝态氮吸收同化的影响,了解苹果愈伤组织对硝态氮亏缺的响应机制,为进一步研究缺氮处理影响愈伤组织生长发育的分子机理提供理论依据。【方法】以‘嘎拉3’组培苗叶片愈伤组织为试材进行组培试验,设置培养基中NO₃–-N亏缺和适宜两个水平 (NO₃–-浓度分别为0 mol/L和0.039 mol/L)。选取叶龄一致的功能性叶片,用灭菌手术刀片沿垂直叶脉方向划伤叶片并切除叶柄和叶尖,叶背向上平铺于MS分化培养基,暗培养3天然后转至光下7天,将长出愈伤组织的叶片分别转移至MS正常分化培养基 (CK) 和MS NO₃–-N亏缺分化培养基 (T,用NH₄Cl、KCl分别代替MS中的NH₄NO₃、KNO₃),培养3周。在转板第0、1、3、7、14、21天分别取叶片伤口处的愈伤组织,观察其细胞形态,测定硝态氮含量、NO₃–流速、氮素同化酶活性和氮素同化酶基因相对表达量。【结果】苹果愈伤组织经NO₃–-N亏缺处理1天后,细胞体积变小,间隙变大,排列疏松,7天后细胞变形,排列无规则。愈伤组织中硝态氮含量在处理7天时达到峰值,为1.54 mg/g,显著高于对照,最大降幅出现在7天后,为13.64%。NO₃–-N亏缺处理前,NO₃–吸收速率最大,为22.38 pmol/(cm2·s),处理1天后降幅为84.1%,处理至7天时,NO₃–已经由吸收变为外排,逆差为24.45 pmol/(cm2·s)。NR活性在处理至7天时无显著变化,7天后快速增加,增幅为19.26%。NiR活性在处理至14天时,无显著性差异,14天后上升幅度为21.83%,缺氮处理1天后,GS活性最低,为0.22 U/g,7天后稍有增加,增幅为22.9%。处理组GOGAT活性在第3天时最低,为0.088 U/g,随后酶活性增加并保持稳定,但是仍低于对照组。处理组氮代谢关键酶基因MdNR2、MdNIR、MdGS2、MdGOGAT的表达量在处理至21天时达到峰值,分别为对照组表达量的3.36、2.52、11.37和2.29倍。【结论】苹果愈伤组织对缺氮非常敏感,从第一天起就可以观测到细胞间隙变大且体积变小,对NO₃–的吸收速率逐渐降低,氮素同化酶活性基本呈逐渐降低的趋势,氮素同化酶基因表达量逐渐升高。缺氮7天后,苹果愈伤组织硝态氮含量趋于稳定,并开始外排NO₃–;氮素同化酶活性基本呈逐渐升高的趋势,氮素同化酶基因表达量进一步升高。总之,氮素亏缺处理前期提高了苹果愈伤组织对NO₃–的吸收,随着处理时间的延长,氮素代谢失衡,严重影响了细胞的形态结构,导致愈伤组织生长发育异常。     

不同肥源对萝卜硝酸盐累积分布和同化的影响

采用田间试验研究了牛粪、化肥单施和配施对萝卜产量,菜体硝酸盐累积、分布、同化,及土壤硝态氮含量变化的影响。结果表明,牛粪、化肥单施和配施,萝卜产量动态变化依次为FOM(1/2化肥+1/2牛粪)、OM(牛粪)F(化肥)CK(无肥),叶部和肉质根硝酸盐含量高低依次为FFOMCKOM,粗蛋白累积量依次为FFOMCKOM,土壤硝态氮含量动态变化依次为FFOMOMCK。综合各因素总体以化肥配施牛粪最为适中,若重点考虑食用安全和土壤硝态氮累积环境效应,则以单施牛粪表现为最佳,各处理引起硝酸盐富集和土壤硝态氮残留的风险依次为化肥(1/2化肥+1/2牛粪)牛粪。萝卜硝酸盐含量分布表现为叶部生长旺盛期叶部硝酸盐含量高于肉质根,肉质根生长旺盛期地下部将贮存更多的硝酸盐。在地上部,当植株硝酸盐富集时,硝酸盐累积在内叶和叶柄中;当植株生长处于养分"饥饿"状态时,硝酸盐释放到外叶和叶片中。因此,菜地连续施用有机肥,不仅可减少蔬菜对硝酸盐的富集,且可维持后期蔬菜产量。     

Diurnal variations in absorption and translocation of a ferrated phytosiderophore in barley as affected by iron deficiency

The release of phytosiderophore (PS) from roots of Fe-deficient graminaceous plants follows a distinct diurnal rhythm with maximum release rates occurring usually 3 to 4 hours after the onset of light. However, it remains to be determined whether absorption of the PS-Fe³⁺ complex shows a diurnal rhythmicity similar to that of PS release, Barley plants grown with or without 10 µM FeEDTA for 7 days were fed with ferreted PS (10 µM labelled with ⁵⁹Fe) at 4-h intervals to study the diurnal variations in the absorption and transloca tion of ⁵⁹Fe, The absorption of ⁵⁹Fe, irrespective of the Fe nutritional status of the plants, was higher during the day and lower during the night but did not show any peak throughout the day-night cycle. On the other hand, the translocation of ⁵⁹Fe into shoots of Fe-deficient plants was lower than that of Fe-sufficient plants, while the Fe nutritional status of the plants did not affect the absorption of ⁵⁹Fe by roots, The formation of root apoplastic ⁵⁹Fe was lower during the day and higher during the night, regardless of the Fe nutritional status of plants. Our results showed that the absorption of the PS-Fe³⁺ complex by roots did not follow the PS release pattern.     

Diurnal uptake of nitrate and potassium during the vegetative growth of tomato plants

Tomato plants (Lycopersicon esculentum Mill.) of the F₁ hybrid variety Turbo were grown in a NFT system for 22 days. On days 16 and 20–22 inclusive of the experiment, the diurnal variation in nitrate (NO₃), potassium (K), and water uptake rates were measured. Nitrate and K uptake rates were subject to large diurnal variation with maximum uptake rates occurring during the day period. Two peaks of diurnal uptake rates were identified, one large peak during the day period and a second much smaller one during the first 2–4 hours of the night. Under the conditions of the experiment, night nutrition made up 35 to 40% of the total daily uptake of K and NO₃. Water uptake rates followed a diurnal oscillation with a single peak pattern. Highest rates occurred at the middle of the photoperiod and lowest rates were measured at night. Over the entire day and night cycle there was no correlation between the rates of water and nutrient uptake. This may be of importance in the fertilization of hydroponically grown plants since in horticultural practice nutrients and water are supplied together in quantities large enough to meet plant water demand but not nutrient requirements.     

Diurnal patterns of methane emissions from paddy rice fields in the Philippines

Methane (CH₄) emissions from rice paddies often show significant diurnal variations, most likely driven by diurnal changes of radiation and temperature in air, floodwater, and soil. Field measurements, however, are often scheduled at a fixed time of a given measuring day, thereby neglecting sub‐daily variations of CH₄ emissions. Here we evaluated diurnal patterns of CH₄ emissions from traditional paddy rice production as observed during field measurements in the Philippines. Field emissions were measured during three consecutive cropping seasons using an automated chamber and gas sampling system with fluxes being obtained every 4 h. Methane fluxes were monitored with a total of nine chambers during the dry seasons in 2012 and 2013 and 27 chambers during the wet season in 2012. Significant and consistent diurnal patterns of CH₄ emissions were mainly observed from the start of field flooding until the middle of cropping periods, i.e., periods with low leaf area of the rice crop. Our data show that disregarding the diurnal variability of fluxes results in an average overestimation of seasonal CH₄ emissions of 22% (16–31%) if measurements were conducted only around noon. Scheduling manual sampling either at early morning (7:00–9:00) or evening (17:00–19:00) results in estimations of seasonal emissions within 94–101% of the “true” value as calculated from multiple daily flux measurements. Alternatively, uncertainties of seasonal emissions can be reduced to an average of ≤3% by applying sinus function or Gauss function‐based correction factors. Application of correction factors allows the performance of flux measurements at any time of day. We also investigated N₂O emissions from rice paddies with respect to diurnal variations, but did not find, as in the case of CH₄, any significant and persistent diurnal pattern.     

Plant growth,photosynthetic pigments,and nitrate assimilation in symbiotic mutants of garden pea

A set of 21 pea (Pisum sativum L.) non‐nodulating mutants and a supernodulating mutant were compared to the parental cv. ‘Finale’ by leaf nitrate reductase activity, nitrogen (N) content in the shoot, content of photosynthetic pigments, and growth. The plants were cultivated asymbiotically at the growth‐saturating nitrate (NO3) level (10 mM) to detect the nitrate assimilation faults. Both positive and negative deviations were revealed in all traits, indicating pleiotropy of symbiotic mutations and/or the deleterious effects of multiple mutations. Only four mutants were indistinguishable from the control plants by all traits. The supernodulating line RisfixC demonstrated lower shoot growth and increased N content in the shoot, in spite of the asymbiotic cultivation.     

Diurnal,shade, and hybrid effects on nitrate content of young corn stalks

Abstract

Significant correlations have been found between the nitrate concentration in young corn (Zea mays L.) stalks and available soi 1 N and relative grain yield when N availability is a yield limiting factor. To successfully use nitrate tissue testing as an indicator of the N status of plants, the effects of factors other than soil or fertilizer N on the nitrate concentration in the tested tissue must be understood. Diurnal effects on stalk nitrate content were studied in a greenhouse experiment, in which stalk samples were collected every two hours for 24 hours, and in a field study, where plants in an N‐fertilizer response experiment were sampled at sunrise and at mid‐day. A significant diurnal cycle was observed for stalk nitrate content in the greenhouse, with a peak at 0800 h and a low at 1400 h, but no diurnal effect was found in the field study, possibly due to plant stress from other environmental factors. In a second greenhouse study, stalk samples from seedlings in direct and 66% shaded natural light were collected for two consecutive days and measured for nitrate content to ascertain the consequences of sampling on overcast days. Significant accumulations of nitrate occurred in stalks of plants sampled after two consecutive days of shading. Stalk samples from three standard hybrid corn trials in central Pennsylvania were measured for nitrate content to determine if hybrid differences existed. Hybrid differences in stalk nitrate were significant in only one of the three sites studied, and the variation in that one may have been due to differences in drought tolerance as well as nitrate metabolism. The results suggest that sampling strategies should be designed to minimize the effects of irradiance level on nitrate accumulation, but that differences in nitrate accumulation among corn varieties may not be a major concern in using nitrate tissue tests to predict N availability.     

Changes in ureide synthesis,transport and assimilation following ammonium nitrate fertilization of nodulated Soybeans 1

The effect of ammonium nitrate fertilization on ureide synthesis, xylem transport and assimilation was examined in four week old nodulated soybean plants. In nodules the activity of 5‐phosphoribosylpyrophosphate amidotransferase, a key enzyme of ureide biosynthesis, declined 75%, while enzymes of purine oxidation (xanthine dehydrogenase and uricase) showed no response to nitrogen treatment. Xylem sap concentrations of allantoin and allantoate, as compared to untreated controls, were reduced by about 85% and 65%, respectively. Despite the substantial decline in ureide synthesis and transport, allantoate concentration in leaves of ammonium nitrate treated plants increased by about three‐fold. No ureide accumulation was observed in leaf tissue following a suppression of ureide formation in nodules by allopurinol, an inhibitor of xanthine dehydrogenase. In the pathway of ureide assimilation in leaves, application of inorganic nitrogen had no effect on activity of allantoinase, but caused a 50% drop in activity of allantoate amidohydrolase. Therefore, the observed accumulation of allantoate in soybean leaves in response to nitrogen fertilization was due to new ureide synthesis in plant tissues other than nodules, or to retardation of ureide degradation in leaves caused by the alternative source of nitrogen.     

Diurnal malate and citrate fluctuations as related to nitrate and potassium concentrations in tomato leaves

Abstract

Two experiments were conducted to determine if malate and citrate change diurnally, if these changes are light dependent, and how these changes relate to K⁺ and NO₃ ^?1 levels. Malate concentration in tomato leaves was shown to increase during the day and decrease at night. The inverse occurred with citrate. The dependency of the changes on light was demonstrated for malate, but not for citrate. A relationship with NO₃ ^? assimilation and K⁺ recirculation may explain the changes in malate concentration.