A model relating the maximum nitrate inflow of lettuce (Lactuca satvia L.) to the growth of roots and shoots

The net inflow of nitrate can be calculated from the nitrate concentration at the root surface by means of the Michaelis-Menten equation. Because of maximum inflow (Imax) is not constant but varies with plant age and growing conditions, a model for calculating Imax during plant growth was derived. Lettuce was grown in nutrient solution. Variations in temperature, radiation and plant age were used to vary growth rates and N-demand of plants. There was a linear relationship between relative growth rates (RGR) and maximum nitrate inflow (Imax), that could be described by the following regression function: Imax = 0.24 + 6.57 RGR. A residual analysis showed a further influence on Imax from the root:shoot-ratio (RSR), the effects of which could be accounted for by including an e-function in the relationship: Imax = (0.27 + 10.63 RGR) e^{(–0.0017 RSR)}. This model for calculating Imax was validated in two further experiments.     

Simulation of the maximum nitrate inflow (Imax) of lettuce (Lactuca sativa L.) grown under fluctuating climatic conditions in the greenhouse

Lettuce was grown in nutrient solution under fluctuating climatic conditions in the greenhouse. The maximum nitrate inflow (Imax) was measured twice a week to validate a model for calculating Imax, that was developed for constant conditions in a growth chamber.Growth and Imax were very similar between greenhouse and growth chamber plants, so that the model was able to predict Imax very precisely. The daily maximum nitrate inflow was calculated and its dependency on fluctuating temperature could be shown.     

Effect of activated charcoal and 6-benzyladenine on in vitro nitrogen uptake by Lagerstroemia indica

A sterile hydroponic culture system suitable for studying nitrogen (N) uptake ofLagerstroemia indica L.in vitro was developed. Four different treatments were assayed: with and without activated charcoal (AC and NAC, respectively), with and without 50 μM of 6-benzyladenine (+BA and −BA, respectively). Medium pH, electrical conductivity (EC), NO₃ ⁻ and NH₄ ⁺ concentrations were measured weekly. At the end of the culture, propagules were sampled and SPAD indices, and shoot and root fresh weights were determined. Explants grown in media with activated charcoal were able to take up both NO₃ ⁻ and NH₄ ⁺, although NH₄ ⁺ uptake was lower. Subsequently the pH of the media was maintained between 5.5–6.0. In treatments with no addition of activated charcoal, NH₄ ⁺ uptake was preferential and the pH dropped to 3.1. Explants in these conditions were unable to raise the pH by taking up NO₃ ⁻, especially when root morphogenesis was inhibited by addition of BA. Supply of this PGR produced root growth inhibition, which was almost complete in the treatment without activated charcoal. This component significantly reduced the inhibitory effect of 50 μM BA on root growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

Modeling magnesium,phosphorus and potassium uptake by loblolly pine seedlings using a Barber-Cushman approach

The Barber-Cushman mechanistic nutrient uptake model, which has been utilized extensively to describe and predict nutrient uptake by crop plants, was evaluated for its ability to predict K, Mg, and P uptake by loblolly pine (Pinus taeda L.) seedlings. Sensitivity analyses were also used to investigate the impact of changes in soil nutrient supply, root morphological, and root uptake kinetics parameters on simulated nutrient uptake. Established experimental techniques were utilized to define the 11 parameters needed to model uptake by 1-0 seedlings of K, Mg, and P from a modified A horizon soil (Lilly series). Model predictions of K and P uptake over a 180-d growth period were underestimated by 6 and 11%, respectively. Estimates of Mg uptake were underestimated by 62%. While the level of agreement between predicted and observed K and P values was quite acceptable, analysis of parameter values and results of sensitivity analyses both indicated that the model underestimation of Mg uptake was the result of applying an I_max value developed under relatively low Mg concentration to a situation in which the functional I_max would be much higher due to the dominance of passive versus active uptake. Overall results of sensitivity analyses indicate that under the circumstances investigated, I_max, was the primary variable controlling plant uptake of K, Mg, and P. The dominance of this term over others was due to the relatively high C_li values for all three nutrients. Reducing (-50%) or increasing (+ 100%) other soil supply, root morphological, and remaining root uptake kinetics values did not substantially alter model estimates of nutrient uptake.     

Modelling the uptake of nitrate by a growing plant with an adjustable root nitrate uptake capacity

A new model is presented to predict the plant uptake of nitrate supplied by diffusion and mass flow to its roots. Plant growth, root-shoot ratio and the plant's nitrate uptake capacity are all set dependent on the plant's N nutrition state. By thoroughly integrating processes occurring in both plant and soil, the model enables to control the relative importance of both under a wide range of different nutritional scenarios.Soil parameters D₀ diffusion coefficient in water (m² day^-1) - D_e diffusion coefficient in soil (m² day^-1) - C nitrate concentration in soil (mol m^-3) - f tortuosity (-) - volumetric moisture content (-) - R radial distance from root axis (m) Plant parameters b₁, b₂ parameters of biomass partitioning Equation (10) - IR interroot distance (m) - K_mU Michaelis-Menten constant of the uptake system (mol m^-3) - K_mNRA Michaelis-Menten constant of nitrogen reduction system (mol g^-1) - k₁, k₂, k₃ parameters of growth model Equation (9) - L_v Root length density (m m^-3) - NO_{3 set} ^- Set point of the cytoplasmatic nitrate pool (mol g^-1 dw) - NO_{3 c} ^- cytoplasmatic nitrate concentration (mol g^-1 dw) - NO_{3 v} ^- vacuolar nitrate concentration (mol g^-1 dw) - NRA_max maximum nitrate reductase activity (mol g^-1 dw day^-1) - N_re reduced nitrogen content (mol) - N_remax maximum reduced N concentration in the plant (mol g^-1 dw) - P partitioning coefficient of nitrate between cyplasm and vacuole - R(1) root radius (m) - RGR relative growth rate (day^-1) - U uptake rate (mol day^-1 m^-2) - U_max maximum uptake rate (Eq. 6) (day^-1 m^-2) - Vo water flux at root surface (m day^-1) - W_r root dry weight (g) - W_sh shoot dry weight (g) - X model parameter: number of root compartments - Y model parameter: number of nodes     

种植密度和施氮水平对小麦吸收利用土壤氮素的影响

2011-2013小麦季,在大田条件下设置2个氮肥水平(180和240kgN· hm-2)和3个种植密度(135、270和405万·hm-2),并将15N-尿素分别标记在20、60和100 cm土层处,研究种植密度-施氮互作对小麦吸收、利用土壤氮素及硝态氮残留量的影响.结果表明:种植密度从135万·hm-2增加至405万·hm-2,小麦在20、60和100 cm土层的15N吸收量分别增加1.86、2.28和2.51 kg·hm-2,地上部氮素积累量和吸收效率分别提高12.6％和12.6％,氮素利用效率降低5.4％;施氮量由240 kg N·hm-2降至180 kg N·hm-2,小麦在20、60 cm土层的15N吸收量分别降低4.11和1.21 kg·hm-2,在100 cm土层的15N吸收量增加1.02 kg·hm-2,地上部氮素积累量平均降低13.5％,氮素吸收效率和利用效率分别提高9.4％和12.2％.施氮180kg N·hm-2+种植密度为405万·hm-2处理与施氮240 kg N·hm-2+种植密度为270或405万·hm-2处理相比,其籽粒产量无显著差异,深层土壤氮素的吸收量显著提高,氮素吸收效率和利用效率分别提高13.4％和11.9％,O～ 200 cm土层的硝态氮积累量及100～ 200 cm土层硝态氮分布比例降低.在适当降低氮肥用量条件下,通过增加种植密度可以促进小麦吸收深层土壤氮素,减少土壤氮素残留,并保持较高的产量水平.     

Modelling the interactions between water and nutrient uptake and root growth

A model of three-dimensional root growth has been developed to simulate the interactions between root systems, water and nitrate in the rooting environment. This interactive behaviour was achieved by using an external-supply/internal-demand regulation system for the allocation of endogenous plant resources. Data from pot experiments on lupins heterogeneously supplied with nitrate were used to test and parameterise the model for future simulation work. The model reproduced the experimental results well (R ² = 0.98), simulating both the root proliferation and enhanced nitrate uptake responses of the lupins to differential nitrate supply. These results support the use of the supply/demand regulation system for modelling nitrate uptake by lupins. Further simulation work investigated the local uptake response of lupins when nitrate was supplied to a decreasing fraction of the root system. The model predicted that the nitrate uptake activity of lupin roots will increase as the fraction of root system with access to nitrate decreases, but is limited to an increase of around twice that of a uniformly supplied control. This work is the first example of a modelled root system responding plastically to external nutrient supply. This model will have a broad range of applications in the study of the interactions between root systems and their spatially and temporally heterogeneous environment.     

Efficiency of nitrate uptake in spinach: impact of external nitrate concentration and relative growth rate on nitrate influx and efflux

Regulation of nitrate influx and efflux in spinach (Spinacia oleracea L., cv. Subito), was studied in short-term label experiments with 13N- and 15N-nitrate. Nitrate fluxes were examined in relation to the N demand for growth, defined as relative growth rate (RGR) times plant N concentration. Plants were grown at different nitrate concentrations (0.8 and 4 mM), with mineral composition of growth and uptake solutions identical. Nitrate influx, efflux and net nitrate uptake rate (NNUR) were independent of the external nitrate concentration, despite differences in internal nitrate concentration. At both N regimes, NNUR was adequate to meet the N demand for growth. RGR-related signals predominantly determined the nitrate fluxes. At high RGR (0.25 g g-1 day-1), nitrate influx was 20 to 40% lower and nitrate efflux was 50 to 70% lower than at lower RGR (0.17 g g-1 day-1); efflux:influx ratio (E:I) declined from 0.5 at low RGR to 0.2 at higher RGR. Thus, the efficiency of NNUR substantially increased with increasing RGR. Differences in nitrate translocation between morning and afternoon coincided with differences in nitrate efflux, which is in accordance with the suggested regulation of nitrate efflux by the root cytoplasmic nitrate concentration. This revised version was published online in July 2006 with corrections to the Cover Date.     

Long-term comparative study of soil nitrate test,Gilat plant indicator method and wheat nitrogen uptake

A long-term comparison between two routine soil nitrogen tests, soil nitrate versus plant indicator method, was performed on the Negev Desert loessial soil in Israel. The Gilat plant indicator method was found to be a better method to reflect the soil nitrogen availability for wheat under field conditions. It was found that 15 to 38 kg ha^-1 of NO₃-N, measured by nitrate soil test, for each 30 cm soil increment, is not available for plant uptake. This plant unavailable NO₃-N background in the soil cannot be leached by repeated irrigation cycles of 100 mm each, or by heavy rains.     

Influence of phosphate status on phosphate uptake kinetics of maize (Zea mays) and soybean (Glycine max)

To obtain plants of different P status, maize and soybean seedlings were grown for several weeks in flowing nutrient solution culture with P concentrations ranging from 0.03–100 µmol P L^-1 kept constant within treatments. P uptake kinetics of the roots were then determined with intact plants in short-term experiments by monitoring P depletion of a 3.5 L volume of nutrient solution in contact with the roots. Results show maximum influx, I_max, 5-fold higher in plants which had been raised in solution of low compared with high P concentration. Because P concentrations in the plants were increased with increase in external P concentration, I_max was negatively related to % P in shoots. Michaelis constants, K_m, were also increased with increased pretreatment P concentration, only slightly with soybean, but by a factor of 3 with maize. The minimum P concentration, C_min, where net influx equals zero, was found between 0.06 and 0.3 µmol L^-1 with a tendency to increase with pretreatment P concentration. Filtration of solutions at the end of the depletion experiment showed that part of the external P was associated with solid particles.It was concluded that plants markedly adapt P uptake kinetics to their P status, essentially by the increase of I_max, when internal P concentration decreases. Changes of K_m and C_min were of minor importance.     

Regulation of urea uptake inPseudomonas aeruginosa

The energy-dependent urea permease was studied in two strains ofPseudomonas aeruginosa, measuring the uptake (transport and metabolism) of¹⁴C-urea. In both strains urea uptakein vivo and urease activityin vitro differed significantly with respect to kinetic parameters, temperature and pH dependence and response to metabolic inhibitors. Ammonium strongly interfered both with the expression of the urea uptake system and its activity. The inhibition of the uptake activity by ammonium was partially relieved by hydraziniumsulfate, which prevented the translocation of ammonium into the cell, and in a methylammonium/ammonium transport-defective mutant of strain DSM 50071. Furthermore, methionine-sulfoximine, which prevented the intracellular glutamine formation from ammoniumvia inhibition of glutamine synthetase, relieved the inhibition of urea uptake by ammonium. These findings suggested that urea uptake activity inP. aeruginosa is regulated by intracellular glutamine.Abbreviations CCCP carbonylcyanide-m-chlorphenylhydrazone - DCCD dicyclohexylcarbodiimide - GS glutamine synthetase - MSX methionine-sulfoximine     

Sink-stimulated photosynthesis and sink-dependent increase in nitrate uptake: nitrogen and carbon relations of the parasitic association Cuscuta reflexa–Ricinus communis

Ricinus communis L. was grown under limiting N supply in quartz sand culture, fed with 0.2, 1 or 5 mol m^?3 NO₃^?, or in liquid culture with 0.022, 0.05 or 0.5 mol m^?3 NO₃^?. Some of the plants were infected with Cuscuta reflexa Roxb. As occurred for the host, dry matter production and growth of C. reflexa were severely depressed with decreasing N supply to the host. When parasitized by C. reflexa, the shoot and root dry weight of Ricinus was diminished at all levels of N nutrition, but the total dry weight of host plus parasite was almost the same as that of uninfected Ricinus. In contrast to the situation in Lupinus albus (Jeschke et al. 1994b), infection by Cuscuta resulted in increased tissue N levels in the host and the N content of the system Ricinus plus C. reflexa was the same or even somewhat larger than that of uninfected plants. This indicated a sink-dependent stimulation of nitrate uptake. As a result of decreased root weights, nitrate uptake g^?1 FW was stimulated by 80, 60 or only 40% at 0.2, 1 or 5 mol m^?3 nitrate supply. Increased nitrate uptake was reflected, particularly at low N supply, in xylem transport; xylem sap nitrate concentrations were substantially elevated, while those of amino acids were decreased in parasitized plants. This indicated an inhibition of nitrate assimilation in roots of parasitized plants under limiting N supply. Besides these effects on N relations, C. reflexa induced a substantial sink-dependent stimulation of net photosynthesis in host leaves and a concomitant increase in stomatal opening and transpiration. This stimulation depended on the relative sink size induced by Cuscuta, on nitrogen nutrition and on leaf age, indicating that delayed senescence of leaves contributes to the overall effects of Cuscuta on its host. The Cuscuta-induced inhibition of nitrate assimilation in the roots and the increase in nitrate uptake suggest that nitrate reduction was shifted towards the leaves in the presence of C. reflexa. The stimulating effects of C. reflexa in the Ricinus-Cuscuta association are compared with the strongly inhibitory effects occurring in the tripartite association L. albus–Rhizobium–Cuscuta reflexa.     

Effect of nitrogen form and root-zone pH on growth and nitrogen uptake of tea (Camellia sinensis) plants

BACKGROUND AND AIMS: Tea (Camellia sinensis) is considered to be acid tolerant and prefers ammonium nutrition, but the interaction between root zone acidity and N form is not properly understood. The present study was performed to characterize their interaction with respect to growth and mineral nutrition. METHODS: Tea plants were hydroponically cultured with NH4+, NO3- and NH(4+) + NO3-, at pH 4.0, 5.0 and 6.0, which were maintained by pH stat systems. KEY RESULTS: Plants supplied with NO3- showed yellowish leaves resembling nitrogen deficiency and grew much slower than those receiving NH4+ or NH(4+) + NO3- irrespective of root-zone pH. Absorption of NH4+ was 2- to 3.4-fold faster than NO3- when supplied separately, and 6- to 16-fold faster when supplied simultaneously. Nitrate-grown plants had significantly reduced glutamine synthetase activity, and lower concentrations of total N, free amino acids and glucose in the roots, but higher concentrations of cations and carboxylates (mainly oxalate) than those grown with NH4+ or NH(4+) + NO3-. Biomass production was largest at pH 5.0 regardless of N form, and was drastically reduced by a combination of high root-zone pH and NO3-. Low root-zone pH reduced root growth only in NO(3-)-fed plants. Absorption of N followed a similar pattern as root-zone pH changed, showing highest uptake rates at pH 5.0. The concentrations of total N, free amino acids, sugars and the activity of GS were generally not influenced by pH, whereas the concentrations of cations and carboxylates were generally increased with increasing root-zone pH. CONCLUSIONS: Tea plants are well-adapted to NH(4+)-rich environments by exhibiting a high capacity for NH4+ assimilation in their roots, reflected in strongly increased key enzyme activities and improved carbohydrate status. The poor plant growth with NO3- was largely associated with inefficient absorption of this N source. Decreased growth caused by inappropriate external pH corresponded well with the declining absorption of nitrogen.     

Modelling the contribution of arbuscular mycorrhizal fungi to plant phosphate uptake

In this paper, we investigate the role of arbuscular mycorrhizal fungi in plant phosphorus nutrition. We develop a mathematical model which quantitatively assesses the contribution of external fungal hyphae to plant phosphate uptake.We derive an equation for solute uptake by a growing fungal mycelium which we couple with a model for root uptake. We analyse the model using nondimensionalization and numerical simulations.Simulations predict that removal of phosphate from soil is dominated by hyphal uptake as opposed to root uptake. Model analysis shows that the depletion zones around hyphae overlap within 8 h and that the transfer between fungus and root is a critical step for the behaviour of phosphorus within the mycelial phase. We also show that the volume fraction of mycelium is negligibly small in comparison to other soil phases.This is the first model to quantify the contribution of mycorrhizal fungi to plant phosphate uptake. A full data set for model parametrization and validation is not currently available. Therefore, more complete sets of experimental measurements are necessary to make this model more applicable.     

Enhancing biological nitrogen removal from tannery effluent by using the efficient Brachymonas denitrificans in pilot plant operations

Summary Laboratory scale and pilot plant reactors were inoculated with an efficient denitrifier, Brachymonas denitrificans(CCUG 45880), in order to evaluate whether a bio-augmentation approach can be used to enhance biological nitrogen removal from tannery effluents. To determine the effectiveness of the introduced strain, denitrifying activity in the activated sludge was monitored by nitrate uptake rate (NUR) measurement of NO₃-N. Fluorescent in situ hybridization (FISH) technique was used to monitor the growth of the augmented species. The laboratory scale nitrate removal efficiency with the introduced B. denitrificans (3.7±0.6 mg NO₃-N gVSS ⁻¹ h ⁻¹) was higher than that of the activated sludge without the addition of the bacteria (3.5±0.7 mg NO₃-N gVSS ⁻¹ h ⁻¹); the NUR in the pilot plant after and before the introduction of the strain was also of the magnitude of 12.0±1.4 and 10.6±1.4 mg NO₃-N gVSS ⁻¹ day ⁻¹ , respectively. In situ hybridization results revealed that the introduced denitrifying bacteria significantly facilitated the development of a dense denitrifying bacterial population in the activated sludge, which enhanced in situ denitrification activity. FISH data indicated that once introduced, B. denitrificans remained abundant throughout the experimental period. The ability to seed a bioreactor with bacterial strain capable of removing target pollutants from tannery effluents in a mixed microbial community suggests that this approach could have commercial applications.     

The influence of temperature and nitrate on vegetative growth and nitrogen accumulation by nodulated soybeans

Summary Inoculated soybeans [Glycine max (L.) Merrill] were grown in controlled environments to evaluate the relationship between temperature and applied NO₃−N on growth rates, N accumulation, and acetylene reduction activity during the vegetative growth stage. Soybeans were grown at day/night temperatures of 22/18 and 26/22°C in sand culture with daily applications of 21.4 mM (high) and 2.1 mM (low) NO₃−N in a complete nutrient solution for durations of 14, 21, and 42 days after emergence and with an N-free solution. Dry matter and N accumulation were greater at 26/22 than 22/18°C. In general, both increased as the level and duration of applied NO₃−N was increased. These increases were attributable to an abbreviation in the interval between emergence and onset of rapid growth. The presence and assimilation of NO₃−N, even at the high level, did not inhibit development of functional nodules. Neither mass nor acetylene reduction activity of nodules was reduced by high NO₃−N; however, the root mass was increased by NO₃−N more than the nodule mass. There was an interaction between temperature and NO₃−N on specific nodule activity as measured by acetylene reduction. The specific nodule activity was unaffected by NO₃−N at 22/18°C, but at 26/22°C the specific activity was lower in the absence of NO₃−N than when NO₃−N was present. Apparently, rapid early growth at 26/22°C depleted cotyledonary reserves of N before nodules became active and, thereafter, the plants were unable to develop adequate leaf area to support nodule development and functioning. This result has implications in N fertilization of late-planted soybeans. Paper number 6637 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, North Carolina, 27650. The research was supported in part by a grant from the North Carolina Soybean Producers Association and by USDA-SEA-CR grant 701-15-26.     

The uptake of nitrate and ammonium nitrogen in Chara hispida L.: the contribution of the rhizoid

Abstract The uptake of ammonium and nitrate nitrogen by cultured plants of the green freshwater alga Chara hispida L. has been compared quantitatively with the contribution of its rhizoidal tissue. In the short-term, the rhizoid takes up 7–20% of the ammonium nitrogen, and about 15% of the nitrate that is taken up by whole plants under similar conditions. The uptake was studied over a range of both temperatures and external concentrations. The apparent activation energy for the uptake of NH₄⁺ and NO₃^? by the whole plant was found to be 50 kJ mol^?1 and 30 kJ mol^?1, respectively. For the rhizoid, the values were similar for both nitrogenous ions, 106 kJ mol^?1 and 70–100 kJ mol^?1. The rhizoidal uptake mechanism for ammonium nitrogen operates more efficiently compared to that in the whole plant. Nitrate is taken up by the rhizoid by a mechanism with a substrate affinity higher than in the plant taken as a whole. The possible ecological significance of the results is discussed.