Effect of Nitrogen and Potassium Stress and Cultivar Differences on Potassium Ions and Nitrate Uptake in Sugarcane

ABSTRACT

This study was conducted to evaluate the effect of nitrogen (N) and potassium (K) stress on nitrate (NO₃ ^?) and potassium ion (K⁺) uptake of two sugarcane (Saccharum officinarum L.) cultivars known to differ with regard to their resistance to drought and salinity stress. The plants were hydroponically grown in a greenhouse and subjected to varying levels of N and K. Nitrogen and K stress increased root affinity for NO₃ ^? and K⁺ absorption by increasing apparent maximum uptake rate (V_max) and decreasing apparent affinity (K_m) for NO₃ ^? and K⁺ uptake in both cultivars. In addition, dry-matter allocation to roots increased with decreasing N and K supply. The results suggest that the acclimation to long-term N starvation in sugarcane involves regulation of both nitrate-specific assimilatory steps and growth responses. The cultivar ‘H69-8235,’ which was drought and salinity resistant, showed greater adaptability to a low- nutrient environment due to its higher root allocation and affinity for NO₃ ^? and K⁺ under N and K stress, suggesting that the resistance of sugarcane to multiple stresses may involve a general stress-response system.     

A comparison of methods for estimating phosphorus uptake kinetics under steady‐state conditions 1

Michaelis‐Menten kinetic parameters (I_max and K_M) are useful for describing nutrient uptake by plants. This paper compares two methods for estimating the kinetics of P uptake. Both methods employed a steady‐state hydroponic system to measure P uptake by wheat (Triticum aestivum L.) seedlings. In one method, uptake was measured from two P concentrations in nutrient solution, with I_max and K_M estimated by direct linear plot (DLP). In an alternate, multiple concentration (MC) method, uptake was measured from five P concentrations, and kinetic parameters were estimated by either nonlinear regression or the Hanes plot. The I_max and K_M, estimates obtained by the DLP method were compared to those obtained by the MC method. The MC method offered practical advantages. Unlike the DLP, it allowed estimation of the external P concentration at which net influx = 0 (C_min), and did not require a priori estimates of K_M and C_min. The MC method provided more precise median parameter estimates as indicated by smaller nonparametric confidence intervals. Using the median C_min value of 1.9 μM, the best estimates of I_max and K_M (and 96% confidence intervals) derived by nonlinear regression were 2.2 (1.6 to 2.8) nmol P g^‐1s^‐1, and 11 (10.6 to 12.9) μM, respectively.     

Effect of nitrate and humic substances of different molecular size on kinetic parameters of nitrate uptake in wheat seedlings

The kinetic parameters of nitrate uptake (I_max, Km and C_min) were evaluated in young seedlings of Triticum durum L., cv. Appulo, exposed to nitrate and/or to soil‐extracted humic acids (HAs) of different molecular weight. The uptake was enhanced after induction at low levels of nitrate (50 μM KNO₃), while it was inhibited after induction at higher concentrations (2000 μM). The kinetic parameters of uptake were selectively influenced by pre‐treatment with HAs: total (TE) and, at a greater extent, low (LMS, < 3500 Da) molecular size humic fraction increased either the nitrate uptake rate (I_max) and the efficiency of the whole transport system (low Km and C_min), while an opposite result was evidenced in high molecular size (HMS, > 3500 Da)‐treated plants. An additive effect was shown when nitrate and humic substances were provided simultaneously: the uptake rate was enhanced in TE‐ and LMS‐treated plants, but was strongly delayed in HMS‐treated plants. Removal of nitrate and/or humic fractions de‐induced the system and NO₃^— uptake rate decreased. Exposure to HAs was not able to induce nitrate reductase activity in root and leaf tissues. Inhibitors of protein synthesis p‐fluorophenylalanine and cycloheximide reversed the positive effect of LMS fraction on nitrate uptake. This would support the hypothesis of a promoting effect of HAs on the molecular expression of proteins of the nitrate transport system.     

NITRATE UPTAKE KINETICS AND METABOLIC PARAMETERS IN TWO RICE VARIETIES GROWN IN HIGH AND LOW NITRATE

A study was conducted on the effect of nitrate (NO₃) levels on nitrate uptake kinetics and nitrogen (N) metabolism in two rice varieties, Piaui (landrace) and IAC-47 (improved). At 27 days after germination (DAG) N supply was suspended for 72 h, and then restored as 0.2 or 2 mM nitrate. The nitrate uptake kinetics was determined by the depletion method. Plants were harvested at 0, 6, and 24 h. Plants of the Piaui variety under 0.2 mM nitrate showed higher V_max and lower K_M, indicating higher efficiency of nitrate uptake at low supply. In the sheaths of both varieties, there was a greater accumulation of nitrate and lower activities of nitrate reductase and glutamine synthetase. The V-H⁺-ATPase activity increased between 0 and 6 h accompanying the nitrate influx, suggesting that the activity of this proton pump is necessary for the antiport activity (H⁺/2NO^? ₃) involved in the accumulation of nitrate into vacuoles.     

Ermittlung kinetischer Parameter der sauren Phosphatasen intakter Zuckerrübenwurzeln bei variierter Phosphaternährung

Determination of kinetic parameters of acid phosphatases in intact sugar beet roots of variable phosphorus nutrition Organically bound phosphorus has to be hydrolysed before its P can be taken up by plants. Both microbes and plant roots possess phosphatases, which could be of importance especially in soils with low concentrations of inorganic phosphorus in the soil solution. This could be the reason why nutrient uptake models underestimate the P-uptake by plants when P-mobilization by the phosphatases of roots is not taken into consideration. Therefore the activity of acid phosphatases (P_ase) was determined to answer the following questions: 1) To which extent does the root bound acid phosphatase (P_ase) follow Michaelis-Menten kinetics? 2) By which of the four linear transformations of the Michaelis-Menten equation (Lineweaver/Burk, Hanes, Eadie/Hofstee, Eisenthal/Cornish-Bowden) can plausible values of V_max and K_m be determined? 3) Which effect has the P nutrition of the plant on these kinetic parameters? Sugar beet plants were grown in full nutrient solution containing 1 and 100 μM P respectively. The P_ase activity of the intact roots was measured at pH 5 using p-nitrophenylphosphate (25—15000 μM p-NPP). V_max values were calculated per m root length. Acid phosphatase activity principally followed Michaelis-Menten kinetics. Transformations and calculations of V_max and K_m after Eadie/Hofstee and Eisenthal/Cornish-Bowden suggested the existence of at least two enzyme systems (P_{ase 1}, P_{ase 2}). The following kinetic parameters were found: P_{ase 1}: P deficient plants: V_max: 43—45 nmol m^—1 min^—1, K_m: 31—37 μM NPP; P sufficient plants: V_max: 7 nmol m^—1 min^—1, K_m: 47—53 μM NPP. P_{ase 2}: P deficient plants: V_max: 230—293 nmol m^—1 min^—1, K_m: 1579—3845 μM NPP; P sufficient plants: V_max: 123—171 nmol m^—1 min^—1, K_m: 3027—7000 μM NPP. Thus plants with sufficient P nutrition have a lower affinity to P_org and a lower hydrolysis of P_org. For P nutrition of crops P_{ase 1} might be the most important enzyme.     

Tomato responses to ammonium and nitrate nutrition under controlled root‐zone pH

Tomato (Lycopersicon esculentum L. Mill. ‘Vendor') plants were grown for 21 days in flowing solution culture with N supplied as either 1.0 mM NO₃ ^‐ or 1.0 mM NH₄ ⁺. Acidity in the solutions was automatically maintained at pH 6.0. Accumulation and distribution of dry matter and total N and net photosynthetic rate were not affected by source of N. Thus, when rhizosphere acidity was controlled at pH 6.0 during uptake, either NO₃ ^‐ or NH₄ ⁺ can be used efficiently by tomato. Uptake of K⁺ and Ca²⁺ were not altered by N source, but uptake of Mg²⁺ was reduced in NH₄ ⁺‐fed plants. This indicates that uptake of Mg²⁺ was regulated at least partially by ionic balance within the plant.     

Correlations between Kinetic Parameters of Phosphate Uptake and Internal Phosphorus Concentrations in Maize Plants: Making it Possible to Estimate the Status of Phosphate Uptake according to Shoot Phosphorus Concentrations

Abstract

The relationship between internal phosphorus (P) concentration [P] and kinetics of phosphate (Pi) uptake was investigated in maize seedlings grown hydroponically at different Pi concentrations (0.1–1,000 µM) and in the phase of Pi deprivation (0–10 d). The results indicated when the internal [P] was higher than 85 µmol g^?1 dw, apparent K_m, C_min, and V_max were significantly (P<0.01) related to [P]s in shoots and roots; when the internal [P] was lower than 85 µmol g^?1 dw, K_m and C_min were small and only V_max was significantly related (P<0.01) to internal [P]s. Three equations were deduced from the linear regressions of the kinetic parameters and [P]s in shoots. Using these equations, the values of apparent K_m, C_min, and V_max of Pi uptake of seedlings grown in different circumstances were calculated according to [P]s in shoots. In all the circumstances involved, for K_m and C_min, there was a parallel relationship between the values estimated by [P]s in shoots and by the Pi‐depletion technique; for V_max, the values estimated by [P]s in shoots were consistent with those obtained from Pi‐depletion experiments except the period of supplying Pi to the Pi‐starved seedlings over several days. These results indicated it is possible to estimate the Pi‐uptake status according to shoot P concentrations in maize plants under experimental conditions, which might be helpful to estimate in‐season status of Pi uptake of maize plants in the field.     

GROWTH AND POTASSIUM TRANSPORT IN COMMON AND DURUM WHEAT AS AFFECTED BY ALUMINUM AND NITRITE STRESS

Aluminum (Al) toxicity has been identified as one of the most important factors limiting plant growth in acid soil. Besides Al, nitrite (NO₂ ^?) may also be a significant stress factor in an acid environment. The objective of this study was to examine the effects of Al and NO₂ ^? stress on the growth and potassium (K⁺) uptake of roots and their transport toward the shoots of an Al-resistant common wheat (Triticum aestivum L. cv. Jubilejnaja 50) and an Al-sensitive durum wheat (T. durum Desf. cv. GK Betadur) grown in 0.5 mM CaSO₄ solution at pH 4.1 or 6.5. Root elongation of durum wheat was inhibited with 30% at 10 μM AlCl₃ treatment, while this low Al-concentration did not show a significant effect on root growth of common wheat. In all cases shoot growth was not influenced under low-salt conditions by 10 μ M AlCl₃, but exposure to 100 μM KNO₂ (alone or in combination with Al) had a definite stimulatory effect on growth. Aluminum was found to stimulate the K⁺(⁸⁶Rb) influx in short-term (6 h) experiments, but to inhibit it in long-term (3 days) experiments. This treatment was thought to damage the plasma membrane. When 10 μM 2,4-dinitrophenol was present in the uptake solution the Al-stimulated K⁺ uptake stopped even in short-term experiments. In the case of nitrite and nitrite + Al treatment combinations, however, a striking inhibition was observed in the K⁺(⁸⁶Rb) influx and the K⁺ concentration of the roots and shoots of both species.     

Mineral nutrition of chickpea plants supplied with NO3 or NH4 N

Chickpea plants (Cicer arietinum L cv. ILC 195) were grown for 24 days in water culture under two regimes of nitrogen nutrition (NO₃ or NH₄‐N) with or without Fe. For plants fed with NO₃‐N, Fe stress severely depressed fresh weight accumulation and chlorotic symptoms of Fe‐deficiency developed rapidly. Little difference in growth occurred in the NH₄‐fed plants, whether or not Fe was withheld, with no visual evidence of Fe‐deficiency indicating a beneficial effect of NH₄ in depressing the symptoms of Fe chlorosis. Typical pH changes were measured in the nutrient solution of the control plants in relation to nitrogen supply, increasing with NO₃ and decreasing with NH₄‐nutrition. With both forms of nitrogen, plants acidified the nutrient solution in response to Fe‐stress. Under NH4‐nutrition, acidification was enhanced by withholding Fe. In the NO₃‐fed plants the uptake of all nutrients was reduced by the stress but proportionally NO³‐ and K⁺ were most affected. Total anion uptake was depressed more than that of cation uptake. For the NH₄‐fed plants withholding Fe resulted in an increased uptake of all ions except NH₄ ⁺ which was depressed. Regardless of the form of N‐supply, when Fe was withheld from the nutrient solution the net H⁺ efflux calculated from the (C‐A) uptake values was closely balanced by the OH” added to the nutrient solution to compensate for the pH changes. Evidence of accumulation of organic acids in the Fe‐stressed plants was found, especially in the NO₃‐fed plants, indicating a role for these internally produced anion charges in balancing cation charge in relation to the depression of NO₃ ^‐ uptake associated with Fe‐stress.     

NaCl对真盐生植物囊果碱蓬硝态氮吸收亲和力系统的影响

采用营养液培养方法,研究了真盐生植物囊果碱蓬(Suaeda physophora Pall.) 在不同盐度和氮水平中预处理21 d后硝态氮的吸收动力学特征。结果表明,氮饥饿后,囊果碱蓬对NO-3吸收符合离子吸收动力学模型,其吸收动力学参数表现为NO-3预处理浓度增加后,高亲和力系统中Vmax增大,Km值增加,但增加的幅度不一致。经过低氮高盐预处理的囊果碱蓬高亲和力系统增加的幅度比经过高氮高盐预处理的囊果碱蓬高亲和力系统增加的幅度大; 对于低亲和力系统,NaCl长期胁迫对高氮预培养的囊果碱蓬的低亲和力系统吸收速率有抑制作用,而对低氮预培养的囊果碱蓬的低亲和力系统吸收速率有促进作用。结果说明,真盐生植物囊果碱蓬长期生长在低氮高盐条件下,为了适应特殊的环境条件,形成了耐盐的硝态氮吸收系统。     

Effect of N‐form on macronutrient and micronutrient concentration and uptake of creeping bentgrass 1

Abstract

Nitrogen‐form effect on nutrient uptake and the subsequent concentration of nutrients in turfgrass plant tissue has not been thoroughly investigated. This study evaluated the effects of clipping regime and N‐form on the tissue concentration of macronutrients and micronutrients and macronutrient uptake in ‘Penncross’ creeping bentgrass (Agrostis palustris Huds.). Turfgrass plugs were grown under greenhouse conditions in a modified Hoagland's solution with a combination of three nutrient solutions (100% NO₃ ^?, 100% NH₄ ⁺, and 50:50 ratio of NH₄ ⁺:NO₃ ^?) and two cutting regimes (cut and uncut). Concentrations of macronutrients and micronutrients were determined for shoot, root and verdure. Nutrient uptake was determined weekly. Uncut NO₃ ^?‐treated plants accumulated higher concentrations of K, Ca, Mg, B and Cu in the shoot tissue; P, K, Ca, Mg, B, Cu, Mn and Zn in the root tissue; and P, Ca, Mg, B, Fe and Mn in the verdure compared to uncut NN₄ ⁺‐treated plants. Nitrate uptake was greater with uncut NO₃ ^?‐treated plants than was NH₄ ⁺ absorption with uncut NH₄ ⁺‐treated plants. Plants grown with the uncut 50:50 treatment adsorbed more NH₄ ⁺ than NO₃ ^?. Plants grown with the uncut NO₃ ^? and 50:50 treatments adsorbed higher amounts of P, K, and Ca compared to the NH₄ ⁺ treatment. The cut NO₃ ^?‐treated plants accumulated higher concentrations of K in the shoot tissue; P, Ca, Mg, B, Cu, Fe and Mn in the root tissue; and B in the verdure than did the cut NH₄ ⁺‐treated plants. Cut NO₃ ^?‐treated plants adsorbed less NO₃ ^? than did cut NH₄ ⁺‐treated plants adsorbed NH₄ ⁺. The cut 50:50 treatment adsorbed more NH₄ ⁺ than NO₃ ^?. Plants grown with NO₃ ^? and 50:50 treatments, under both cutting regimes, resulted in higher concentrations of most macro‐ and micronutrients and greater nutrient uptake compared to the NH₄ ⁺‐treated plants.     

Kinetics of soil microbial uptake of free amino acids

 Amino acids and proteins typically form the biggest input of organic-N into most soils and provide a readily available source of C and N for soil microorganisms. Amino acids can also be taken up directly by plant roots, providing an alternative source of available soil N. However, the degree to which plants can compete against the soil microbial population for amino acids in soil solution remains poorly understood. The aim of this study was to measure the rate of microbial uptake of three contrastingly charged ¹⁴C-labelled amino acids (glutamate^1–, glycine⁰, lysine^0.9+) over a wide concentration range (0.1–5 mM) and in two contrastingly managed soils varying in their degree of erosion, organic-C content and microbial biomass. Amino acid uptake was concentration dependent and conformed to a single Michaelis-Menten equation. The mean maximum amino acid uptake rate (V _max) for the non-eroded (control) soil (high organic-C, high biomass) was 0.13±0.02 mmol kg^–1 h^–1, while half maximal uptake occurred at a concentration (K _m) of 2.63±0.07 mM. Typically, V _max was fourfold lower and K _m twofold lower in the eroded soil (low available organic-C, low biomass) compared to the non-eroded (control) soil. Amino acid substrate concentration had little effect on the proportion of amino acid utilized in catabolic versus anabolic metabolism and was similar for both. While the results obtained here represent the summation of kinetics for a mixed soil population, they indicate that amino acid uptake is saturated at concentrations within the millimolar range. Because the affinity constants also were similar to those described for plant roots, we hypothesized that competition for amino acids between plants and microbes will be strong in soil but highly dependent upon the spatial distribution of roots and microbes in soil. Received: 2 March 2000     

Nitrate influx in rose plants during day-night cycle

In herbaceous plants grown in controlled environmental conditions nitrate (NO₃^?) uptake increases during the day and decreases in the night. The aim of this work was to measure NO₃^? uptake rates along the day-night cycle, in rose (Rosa hybrida L.) plants grown under controlled environmental conditions. Two independent experiments were conducted inside a growth chamber at 20 ºC and 25 ºC, using rose mini-plants cv. Texas, grown in a hydroponic nutrient film technique (NFT) set-up with at 3.0 mol m^?3 NO₃^? concentration. Dry matter and nitrogen (N) accumulation were registered during growth and NO₃^? uptake rates were measured during a day-night cycle, using ¹⁵N as ¹⁵NO₃^?. In both experiments the hourly estimated N-NO₃^? accumulation rates are near to the measured uptake rates of ¹⁵NO₃^? and nitrate uptake decrease during the day and increase in the night, in contrast with the herbaceous plants. Results are discussed on the basis of N plant demand and carbohydrates availability.     

The influence of the growth media and mineral nutrition on corn root hydrogen / bicarbonate releases and rhizosphere pH

A study was made of the influence of substrate on the root releases of hydrogen ions (H+) and bicarbonate ions (HCO₃ ^‐) by corn (Zea mays, cv.Dea) grown between the 5/6 leaf and the 9/10 leaf stage in two different growth media, siliceous or calcareous sand. Different nutrient solutions were supplied in separate experiments, but in all cases, nitrogen was in the form of nitrate (NOg"), and iron chelates were present in solution.

In siliceous sand the pH generally increased, but acidification appeared with low NO₃ ^‐ nutrition. Roots released H⁺ and HCO₃ ^‐ simultaneously, and these ions partially reacted to form H₂CO₃. The pH variations depended on the balance of the released ions and on the low buffer capacity in this slightly acidic pH range. The algebraic sum of the ion effluxes was approximately equal to the sum of the ion uptakes; no stoichiometric coupling between the total H⁺ effluxes and the NO₃ ^‐ or potassium (K⁺) uptakes was recorded.

In calcareous sand HCO₃ ^‐ was released by the roots, but the H⁺ seedling effluxes always acidified the solutions with regard to the reference solutions in calcareous sand without plants. Even though HCO₃ ^‐ was released in great quantities by plants, the pH of the solutions did not become alkaline because of the high buffer capacity of the solution in contact with the calcareous medium. In this environment the plants reacted to the high levels of HCO₃ ^‐ and showed symptoms of lime‐induced chlorosis. To overcome the poor physicochemical conditions, H⁺ was released from the corn roots, and this H⁺ efflux was correlated to the total alkalinity of the solution.     

Effect of nitrogen form during the flowering period on zucchini squash growth and nutrient element uptake

Zucchini squash (Cucurbita pepo L. cv. Green Magic) plants were grown hydroponically with nitrate (NO₃):ammonium (NH₄) ratio of 3:1 until the onset of flowering when the plants were assigned to four NO₃:NH₄ ratio (1:0, 1:1, 1:3, or 3:1) treatments. Changing the original nitrogen (N) form ratio significantly affected plant growth, fruit yield, nutrient element, and water uptake. Growth of plants was better when NO₃‐N (1:0) was the sole form of N than when NH₄‐N was part of the N treatment. Fruit yields for plants fertilized with 1:0 or 1:3 N‐form ratio were double those of plants grown continuously with 3:1 N ratio. The largest leaf area and plant water use were obtained with 1:0 N ratio treatment Total uptake of calcium (Ca), magnesium (Mg), and potassium (K) decreased with increasing NH₄‐N proportion in the nutrient solution which suggest NH₄‐N was competing with these cations for uptake. The results also demonstrated that growers may increase fruit yield by using a predominantly NO₃‐N source fertilizer through the vegetative growth stage and by shifting the NO₃:NH₄ ratio during the reproductive phase.     

Modeling the uptake of sulfur by crops on two alluvial soils of Louisiana: Cotton

Abstract

The Cushman and Barber mechanistic model was used to help elucidate the mechanisms that govern the uptake of sulfur (S) by plants. Sulfur uptake predicted by the model was compared to measured S uptake by cotton, (Gossypium hirsutum [L]) grown on Mhoon silty clay loam (Typic Fluvaquent) and a Norwood silt loam (Typic Udifluvent) under glasshouse conditions. Predicted S uptake was significantly correlated with observed uptake r²=0.71. However, the model overpredicted S uptake by a factor of 3.5. The assumption that the maximun ion Influx rate (I _max) for roots growing in soils is the same as the I_max measured in solution cultures experiments may not be appropriate. Better agreement between observed and predicted S uptake values was achieved by using an estimated I_max obtained from soil studies (I_s) with the method of Warncke and Barber. Using I, predicted vs observed S uptake had a slope of 1.00 and r²=0.93. The model predicted that S concentration in soil solution (C_lo) at the root surface (r_o) increased with time for soils with initial S concentration in solution of lmM or higher. This high C_lo, will trigger a higher I_s of about 4 nmol/m²sec, while plants grown on soils with low S content will show a lower I_s, suggesting that S uptake by cotton plants is biphasic and depends on C_lo at r_o.     

Potassium recirculation in tomato plants in relation to potassium supply

The Ben Zioni ‐ Dijkshoorn hypothesis that NO₃ uptake by roots is regulated by NO₃ assimilation in the shoot was tested using the tomato plant. Plants were grown at three K levels and the fate of anion charge from NO₃,^‐ and SO₄ ^2‐. assimilation followed in its distribution between organic acid anion accumulation and HCO₃ ^‐ efflux into the nutrient medium. For the high K treatment almost all of this charge was directed towards organic acid accumulation with HCO₃ ^‐ efflux accounting for only 3% of the total charge. On the other hand for plants supplied at the low K level, a substantial proportion of the anion charge was excreted as HCO₃ ^‐ (32%).

Xylem sap analyses and NO₃ reductase assay results indicated that in the tomato plant the upper plant parts constituted the major site for NO₃ reduction. The quantitatively most important ionic constituents in the sap were K⁺, Ca²⁺ and NO₃ ^‐.

Results have been presented that indicate that when K is in short supply in the nutrient medium, K recycling occurs within the plant to facilitate the upward transport of NO₃ ^‐ from root to shoot.     

Potassium,nitrogen, ammonium/nitrate ratio,and sodium chloride effects on wheat growth

Fertigation with KNO₃ as a means of reducing salinity hazards was tested with peanut (Arachis hypogaea) plants grown on dune sand, resulting in a reduction of plant growth and yield. The objective of this work was to study the interactions between N, K⁺ and NaCl as well as the effects of the NH₄ ⁺/NO₃ ^‐ ratio on vegetative and reproductive growth. Wheat (Triticum aestivum L.) plants were grown in polyethylene pots with fine calcareous dune sand with different proportions of NH₄ ⁺ and NO₃ ^‐, under saline (60 mM NaCl) and non‐saline conditions. Three replicates were harvested at the beginning of flowering, and one was grown to grain maturity. NaCl reduced shoot dry weight in all the treatments. Increasing the NH₄ ⁺ proportion in the total of 6 mM N in the nutrient solution, increased shoot dry weight, did not change nitrogen concentration in the dry mass but increased P percentage, either with or without 60 mM NaCl. The number of tillers produced in each treatment was correlated with dry matter yield. The effect of the NH₄ ⁺/NO₃ ^‐ ratio may be explained by alteration of the cation‐anion balance on the nutrient uptake by roots, which lowered pH of the nutrient solution with increasing NH₄ ⁺ concentration, by alteration of the cation‐anion balance on the nutrient uptake by roots, which lowered pH of the nutrient solution with increasing NH₄ ⁺ concentration.     

Ethylene evolution and ammonium accumulation by nutrient‐stressed tomato plants

Environmentally stressed plants frequently have elevated rates of ethylene evolution and high accumulation of free ammonium by their foliage. The objective of this study was to investigate ethylene evolution and ammonium accumulation by nutrient‐deficient and ammonium‐stressed tomato plants (Lycopersicon esculentum Mill. ‘Heinz 1350’ and neglecta‐1) grown in a greenhouse. In soil culture, ‘Heinz 1350’ was more sensitive to ammonium toxicity and had higher ethylene evolution than neglecta‐1. High ethylene evolution corresponded with appearance of ammonium toxicity symptoms in both lines. In sand culture, ‘Heinz 1350’ and neglecta‐1 grown with K, Ca, or Mg deficiency in NO₃ ^‐‐based nutrient solutions had higher ammonium accumulation and higher ethylene evolution than plants grown with complete nutrition. P‐deficient plants had elevated ammonium accumulation but low ethylene evolution. Plants grown on NH₄ ⁺‐based nutrition with pH buffering by CaCO₃ had lower ethylene evolution and lower ammonium accumulation than plants grown in unbuffered solutions but had higher values than plants grown with NO₃ ^‐‐based nutrition. Adequate K nutrition suppressed ethylene evolution and ammonium accumulation for all plants regardless of nitrogen regimes. Ammonium accumulation and ethylene biosynthesis in plants appear to be related processes. They appear to be indicators of stress and may have roles in development of symptoms of nutritional stresses.     

Kinetics of Nitrification in Selected Iowa Soils Treated with Stay‐N 2000

Abstract

The effectiveness of Stay‐N 2000 or reformulated nitrapyrin [2‐chloro‐6‐(tricholoromethyl) pyridine] was investigated in two Iowa soils representative of Clarion and Okoboji soils that differed in organic carbon, pH, and texture. A nonlinear regression was used to estimate kinetic parameters. The maximum nitrification rate (K _max) and the duration of lag period (t′) were derived from the equation to characterize the nitrification process in both soils. Stay‐N 2000 appeared to be a better inhibitor than nitrapyrin to extend t′ and as effective as nitrapyrin in reducing K _max. Stay‐N 2000 reduced K _max an appreciable amount in the Okoboji soil at the rate of 12 µg a.i. g^?1 soil or three times the recommended rate. Nitrification rates were affected by the rates of nitrogen (N) applied to both soils; the higher the N rates, the higher K_max, and the more the nitrate (NO₃ ^?)‐N accumulation.