Uptake Rates Of NO3 Research Articles

Oxidative and reductive microbial consumption of nitric oxide in a heathland soil

An acidic heathland podzol exhibited almost zero rates of NO production but high rates of NO consumption. The NO uptake rate constants decreased with soil depth. They were about two times higher and exhibited different kinetic characteristics under oxic than under anoxic incubation conditions. Under anoxic conditions, NO uptake followed Michaelis-Menten kinetics with K m values around 1 ppmv NO (1 μl NO 1 −1 gas phase). Similar kinetics are known from the literature for NO reduction by denitrifying bacteria. Anoxic NO uptake was stimulated by addition of nitrate and glucose. When the podzol was gassed with nitrogen containing 9.5 ppmv NO, most (94%) of the anoxically-consumed NO was recovered as N 2O demonstrating that NO was consumed by denitrification to N 2O. Under oxic conditions, on the other hand, NO uptake followed apparent first-order kinetics up to NO mixing ratios of >4ppmv, suggesting a NO consumption pathway different from denitrification. Uptake of NO was abolished by autoclaving and exhibited a temperature optimum at 40°C demonstrating that it was due to biological activity. The activity exhibited a sharp optimum at the in-situ pH of 3.3, and a broad optimum at soil moistures between 10 and 60% of the maximum water holding capacity. Oxic NO uptake was not stimulated by addition of nitrate plus glucose. When the podzol was gassed with air containing 9.5 ppmv NO, only a small proportion (5%) of the consumed NO was recovered as N 2O. Instead, labelling experiments with 15NO showed that most (90±17%) of the oxically consumed NO was converted to 15NO 3 −. Our results show that NO is consumed in soil both by oxidation to nitrate and by reduction through the denitrification pathway depending on oxic or anoxic conditions, respectively.

Flux between soil and atmosphere, vertical concentration profiles in soil, and turnover of nitric oxide: 2. Experiments with naturally layered soil cores

Intact soils cores were taken with a stainless steel corer from a sandy podzol and a loamy luvisol, and used to measure the flux (J) of NO between soil and atmosphere and the vertical profile of the NO mixing ratios (m) in the soil atmosphere, both as function of the NO mixing ratio (ma) in the atmosphere of the headspace. These measurements were repeated after stepwise excavation of the soil column from the top, e.g. by removing the upper 2 cm soil layer. The gaseous diffusion coefficients of NO in the soil cores were either computed from soil porosity or were determined from experiments using SF6. The NO fluxes (J) that were actually measured at the soil surface were compared to the fluxes which were calculated either from the vertical NO profiles (J c ) or from the NO production and uptake rates (J m ) determined in the excavated soil samples. In the podzol, the actually measured (J) and the calculated (J m , Jm) NO fluxes agreed within a factor of 2. In the luvisol, the measured NO fluxes (J) and those calculated from the vertical NO profiles (J c ) also agreed well, but in the upper 6 cm soil layer the NO fluxes (J m ) calculated from NO production and uptake rates were up to 7 times higher than the measured NO fluxes. This poor agreement was probably due to the inhomogeneous distribution of NO production and consumption processes and the change of diffusivities within the top layers of the luvisol. Indeed, the luvisol showed a pronounced maximum of the NO mixing ratios at about 6 cm depth, whereas the podzol column exhibited a steady and exponential decrease of the NO mixing ratios with depth. The inhomogeneities in the luvisol were confirmed by incubation of the soil cores under anoxic conditions. This treatment resulted in production of NO at several depths indicating a zonation of increased potential activities within the luvisol profile which may have biased the modelling of the NO surface flux from turnover measurements in soil samples. Inhomogeneities could be achieved even in homogenized soil by fertilization with nitrate solution.

Flux between soil and atmosphere, vertical concentration profiles in soil, and turnover of nitric oxide: 1. Measurements on a model soil core

A stainless steel soil corer which was filled with homogenized soil was used to measure the flux (J) of NO between soil and atmosphere and the vertical profile of the NO mixing ratios (m) in the soil atmosphere, both as function of the NO mixing ratio (mma) in the atmosphere of the headspace. The NO emission flux decreased linearly with increasing NO mixing ratio and turned into a deposition flux after passage of the compensation point (mc) at about 400 ppbv NO. Almost the same compensation point was obtained when the turnover of NO was measured in flask-incubated soil samples as function of the NO mixing ratio. The flux (J) of NO at the soil-atmosphere interface was calculated from the production rate (P) of NO and the NO uptake rate constant (k) that were measured in these flask-incubated soil samples using the diffusion model of Galbally and Johansson (1989). The calculated fluxes agreed within <15% with those actually measured. The vertical profiles of NO were fitted to an exponential function and analyzed by Fick's first law of diffusion. The shape of the profiles indicated a net production of NO in the upper 10 cm soil layer when the atmospheric NO mixing ratio was below the compensation point and in a net consumption of NO when the atmospheric NO mixing ratio was above the compensation point. In soil layers below 10 cm depth, the turnover of NO resulted in compensation of production and consumption rates. Measurement of the actual diffusion coefficient using SF6 showed that gas transport in the soil core was not only due to molecular diffusion but in addition due to a bidirectional gas flow. The experimentally determined diffusion coefficient was smaller than that computed from soil porosities, but resulted together with the additional transport term in NO fluxes that were close (< ±15%) to those measured. This is the first comprehensive study of NO concentration profiles and turnover rates in soil providing a theoretical basis for modelling NO fluxes at the soil-atmosphere interface.

Morphology and Physiology of the Seminal Root System of Young Maize (Zea mays L.) Plants as Influenced by a Locally Restricted Nitrate Supply

AbstractIn water culture the effect of a locally restricted NO3 supply to the seminal root system of maize seedlings was studied. For this purpose plants were cultivated in containers with a wide‐bore polyethylene tube positioned horizontally. Roots were suited through small holes in this tube and after sealing the holes with a non‐toxic silicon putty, root segments in the tube could be exposed to a different nutrient solution from the rest of the root system in the outer compartment.In case of a locally restricted NO3 supply (NO3 was just supplied to the root segment within the tube), we observed an increase in root growth beginning at the fifth day after onset of the treatment. NO3 uptake rate (15N) within the tube was significantly higher than in control plants (receiving NO3 to the entire root system) as early as two days after onset of the treatment. One day later respiration (O2 consumption) of the root segment exposed to NO3 increased and at the same day we observed an accumulation of 14C activity (after pulse labelling of the shoots with 14CO2) suggesting an increased phloem unloading. It is argued that this leads to the measured increase in IAA activity (Radio Immuno Assay) in the zone of NO3 supply. Beginning at the fifth day we observed a stimulation of cell division rate (incorporation of 3H‐methylthymidine), accompanied by an increase in length of first order lateral roots.

Nitrogen Uptake and Partitioning in Response to Reproductive Sink Size of Soybean

During reproductive development, seeds become a dominant sink for both carbon and nitrogen. To determine how nitrogen uptake and partitioning by nonnodulated soybean (Glycine max [L.] Merrill) are affected by a reduced pod load, all pods, ca. half of all pods, and no pods were removed at the beginning of seed fill from plants growing in flowing solution culture containing 1.0 mM NO3 -. Dry matter and nitrogen distributions within the plants were determined at periodic harvests. Net uptake rates of NO3 - and net CO2 exchange rates of leaves were measured daily during the subsequent 25-d period of seed fill. Net uptake rates of NO3 - were determined by ion chromatography as depletion from replenished solutions. For plants with a full pod load, both NO3 - uptake and CO2 exchange rates were maintained throughout the 25-d period of seed fill. With partial and complete depodding, the CO2 exchange rates of the upper, most photosynthetically active leaves declined during the final 5-10 d of seed fill. Net NO3 - uptake rates, particularly by completely depodded plants, were slightly enhanced during the initial 10-15 d after depodding until emergence of additional leaves established new sinks for the photosynthate normally partitioned to reproductive growth in plants with full pod loads. The initially enhanced uptake rates of NO3 -, however, were not of sufficient magnitude to contribute to a significant increase in accumulation of nitrogen in the depodded plants. These results indicate that photosynthetic capacity is sufficient to support both reproductive growth and nitrogen acquisition when soybeans are grown nearly without environmental stress.

Nitrate and ammonium uptake by wheat seedlings as affected by salinity and light

Abstract Nitrate (NO3‐) and ammonium (NH4+) are the two main forms of nitrogen (N) taken up by plants. Several environmental factors affect the uptake of N. This work was undertaken to study the induction of NO3‐ and NH4+ transport systems in wheat (Triticum aestivum L.) roots as affected by salinity and light. Wheat seedlings were germinated in sterilized vermiculite and plants were grown in a growth chamber under controlled conditions for eight days with a nutrient solution without N, and with or without sodium chloride (NaCl). Uptake rates of NO3% NH4+, or NH4++ NO3‐ were calculated by measuring the disappearance of N from the solutions. The NO3‐ uptake developed with time, either through induction or activation. Salinity pretreatments increased net uptake rates of NO3‐ and NH4 +, suggesting that plants were in a higher N‐deficient status when grown in saline conditions. Light decreased initial NO3”; uptake but had little effect on initial NH4+ uptake.

A study to explain the emission of nitric oxide from a marsh soil

In the period 18–21 September 1989, soil NO emission was studied at Halvergate Marshes, Norfolk (U.K.) within the framework of the BIATEX-LOVENOX joint field experiment. Using a dynamic chamber technique, 186 measurements at four plots were performed showing a net NO flux of 7.2−14.6×10−12 kgN m−2 s−1. Soil samples from a soil profile (1.0 m) at a representative site and from the uppermost layer (0.1 m) of each of the four plots were sent to the laboratory for (a) detailed physical and chemical soil analysis, (b) determination of NO production rates, NO uptake rate constants, and NO compensation mixing ratios, and (c) characterization of the microbial processes involved. A diffusive model (Galbally and Johansson, 1989) was applied to the laboratory results to infer NO fluxes of the individual soil samples. When we compared these fluxes with those measured in the field, we found agreement within a factor 2–4. Furthermore, laboratory studies showed, that NO was produced and consumed only in the upper soil layer (0–0.1 m depth) and that the NO production and consumption activities observed in the Halvergate marsh soil were most probably due to the anaerobic metabolism of denitrifying bacteria operating in anaerobic microniches within the generally aerobic soil.

Influence of the Form of Nitrogen Supply on Root Uptake and Translocation of Cations in the Xylem Exudate of Maize (Zea maysL)

Concentrations of inorganic cations are often lower in plants supplied with NH4+ as compared with NO3−. To examine whether this is attributable to impaired root uptake of cations or lower internal demand, the rates of uptake and translocation of K, Mg, and Ca were compared in maize plants (Zea mays L.) with different growth-related nutrient demands. Plants were grown in nutrient solution with either 1·0 mol m−3 NO3− or NH4+ and the shoot growth rate per unit weight of roots was modified by varying the temperature of the shoot base (SBT) including the apical shoot meristem. The shoot growth rate per unit weight of roots, which was taken as the parameter for the nutrient demand imposed on the root system, was markedly lower at 12°C than at 24°C SBT. As a consequence of the lower nutrient demand at 12°C SBT, uptake rates of NO3− and NH4+ declined by more than 50% Compared with NO3− supply, NH4+ nutrition depressed the concentrations of K and particularly of Ca in the shoot, both in plants with high and with low nutrient demand. This indicates a control of cation concentration by internal demand rather than by uptake capacity of the roots. Translocation rates of K, Mg and Ca in the xylem exudate were lower in NH4+- than in NO3−-fed plants. Net accumulation rates of Ca in the shoot were also decreased, whereas net accumulation rates of K in the shoot were even higher in NH4+-fed plants. It is concluded that reduced cation concentrations in the xylem sap of plants supplied with NH4+ are due to the lower demand of cations for charge balance. The lower K translocation to the shoot is compensated by reduced retranslocation to the roots. For Ca, in contrast, decreased translocation rates in NH4+-fed plants result in lower shoot concentration.

Effects of soil variables and season on the production and consumption of nitric oxide in oxic soils

NO production rates, NO uptake rate constants, NO compensation points, and different soil variables were determined for various soil types and different soil horizons, and checked for mutual correlations. NO production was detected in all, and NO comsuption in most soils tested. Only soils in a very early state of soil genesis showed no NO consumption activity. NO consumption was positively correlated with soil water and NH 4 + contents. NO production rates were not correlated with any soil variable. Both NO production and NO consumption tended to decrease from the upper organic to the deeper mineral horizons in different climax soils. The seasonal variation of NO production and NO consumption in a calcic cambisol and a luvisol showed highest rates in summer. The rates of NO production and NO consumption were correlated with a few of the soil variables, but showed no uniform, theoretically comprehensible pattern. However, NO production in samples of the calcic cambisol was stimulated by fertilization with NH 4 + , but not with NO 3 − and was inhibited by nitrapyrin, indicating that NO was produced by nitrification. NO production made up about 3% of the nitrification rates. In the luvisol, in contrast, NO production was not affected by the addition of NH 4 + or NO 3 − . Nitrification was also undetectable in this acidic soil, except for a few patches where NO production was also detected.

Ammonium and nitrate uptake rates and rhizosphere pH in non-mycorrhizal roots of Norway spruce [Picea abies (L.) Karst.

Relationships between root zone temperature, concentrations and uptake rates of NH 4 + and NO 3 − were studied in non-mycorrhizal roots of 4-year-old Norway spruce under controlled environmental conditions. Additionally, in a forest stand NH 4 + and NO 3 − uptake rates along the root axis and changes in the rhizosphere pH were measured. In the concentration (Cmin) range of 100–150 μM uptake rates of NH 4 + were 3–4 times higher than those of NO 3 − The preference for NH 4 + uptake was also reflected in the minimum concentration (Cmin) values. Supplying NH4NO3, the rate of NO 3 − uptake was very low until the NH 4 + concentrations had fallen below about 100 μM. The shift from NH 4 + to NO 3 − uptake was correlated with a corresponding shift from net H+ production to net H+ consumption in the external solution. The uptake rates of NH 4 + were correlated with equimolar net production of H+. With NO 3 − nutrition net consumption of H+ was approximately twice as high as uptake rates of NO 3 − In the forest stand the NO 3 − concentration in the soil solution was more than 10 times higher than the NH 4 + concentration (<100 μM), and the rhizosphere pH of non-mycorrhizal roots considerably higher than the bulk soil pH. The rhizosphere pH increase was particularly evident in apical root zones where the rates of water and NO 3 − uptake and nitrate reductase activity were also higher. The results are summarized in a model of water and nutrient transport to, and uptake by, non-mycorrhizal roots of Norway spruce in a forest stand. Model calculations indicate that delivery to the roots by mass flow may meet most of the plant demand of nitrogen and calcium, and that non-mycorrhizal root tips have the potential to take up most of the delivered nitrate and calcium.

Influence of oxygen on production and consumption of nitric oxide in soil

NO and N2O release rates were measured in an acidic forest soil (pH 4.0) and a slightly alkaline agricultural soil (pH 7.8), which were incubated at different O2 concentrations (<0.01 – 20% O2) and at different NO concentrations (40 – 1000 ppbv NO). The system allowed the determination of simultaneously operating NO production rates and NO uptake rate constants, and the calculation of a NO compensation concentration. Both NO production and NO consumption decreased with increasing O2. NO consumption decreased to a smaller extent than NO production, so that the NO compensation concentrations also decreased. However, the NO compensation concentrations were not low enough for the soils to become a net sink for atmospheric NO. The release of N2O increased relative to NO release when the gases were allowed to accumulate instead of being flushed out. The forest soil contained only denitrifying, but not nitrifying bacteria, whereas the agricultural soil contained both. Nevertheless, NO release rates were less sensitive to O2 in the forest soil compared to the agricultural soil.

Study on nutrient stress tolerance of nine Taraxacum microspecies with a contrasting mineral ecology by cultivation in a low nutrient flowing solution

Growth and mineral status of 9 Taraxacum microspecies were studied under mineral stress conditions, using a flowing solution of low nutrient concentration. Relative growth rate of (whole) plant dry weight, leaf area, and (whole) plant tissue water were used to describe growth. For 4 microspecies, specific uptake rates of NO−3, H2PO−4, K+, Mg2+ and Ca2+ were investigated.The applied nutrient condition clearly discriminated between the studied Taraxacum microspecies. With respect to relative growth rate, 3 groups of microspecies could be distinguished: T. nordstedtii &gt; T. lancidens, T. adamii, T. hollandicum, T. taeniatum &gt; T. sellandii, T. eudontum, T. ekmanii, T. ancistrolobum. These categories coincided well with the mineral ecology of the microspecies, going from infertile to fertile sites. T. nordstedtii, a microspecies of infertile sites, was most efficient in absorbing NO−3, H2PO−4 and K+. T. sellandii and T. eudontum, both occurring in fertile grasslands, showed poor uptake performances for all studied ions. In all Taraxacum microspecies studied, except T. eudontum, internal N concentration appeared to limit growth. Efficiencies in N use, at sub‐optimal internal N concentrations, varied with the mineral habitat of the microspecies studied. T. nordstedtii, from infertile sites, and T. sellandii, from fertile sites, were established as high and low extremes, respectively.

Nitrogen nutrition of ectomycorrhizal symbionts

Inorganic nitrogen nutrition was studied on isolated partners of ectomycorrhizal associations. The growth of maritime pines ( Pinus pinaster) was measured with NO 3 − or NH 4 + as N source. Seedling weights were greater on NH 4 + than on NO 3 −. The ionic balances were established in both types of nutrition suggesting that nitrate reduction was mainly carried out in the roots. The uptake rates of NO 3 − or NH 4 + by fungal species were measured by using assimilation of 15N labelled nitrogen: with suitable carbon source, the uptake rates of NH 4 + were higher than the the uptake rates of NO 3 −. The ionic balances were established in both types of nutrition and suggested that nitrate reduction does not result in a high level of carboxylate production.

Cyclic variations in nitrogen uptake rate in soybean plants: uptake during reproductive growth.

Net uptake of NO3- by non-nodulated soybean plants [Glycine max (L.) Merr. cv. Ransom] growing in flowing hydroponic culture was measured daily during a 63 d period of reproductive development between the first florally inductive photoperiod and [unknown word] seed growth. Removal of NO3- from a replenished solution containing 1.0 mol m-3 NO3- was determined by ion chromatography. Uptake of NO3- continued throughout reproductive development. The net uptake rate of NO3- cycled between maxima and minima with a periodicity of oscillation of 3 to 7 d during the floral stage and about 6 d during the fruiting stage. Coupled with increasing concentrations of carbon and C : N ratios in tissues, the oscillations in net uptake rates of NO3- are evidence that the demand for carbohydrate by reproductive organs is contingent on the availability of nitrogen in the shoot pool rather than that the demand for nitrogen follows the flux of carbohydrate into reproductive tissues.

Microbial production and uptake of nitric oxide in soil

Fluxes of NO from three different soils have been studied by a flow-through system in the laboratory as a function of gas flow rate, of NO mixing ratio, and of incubation conditions. The dependence of net NO fluxes on gas flow rates and on NO mixing ratios could be described by a simple model of simultaneous NO production and NO uptake. By using this model, rates of gross NO production, rate constants of NO uptake, and NO compensation mixing ratios could be determined as function of the soil type and the incubation condition. Gross NO production rates were one to two orders of magnitude larger under anaerobic than under aerobic conditions. NO uptake rate constants, on the other hand, were only 5–8 times larger so that the compensation mixing ratios of NO were in a range of about 1600–2200 ppbv under anaerobic and of about 50–600 ppbv under aerobic conditions. The different soils exhibited similar NO uptake rate constants, but the gross NO production rate and compensation mixing ratio was significantly higher in an acidic (pH 4.7) sandy clay loam than in other less acidic soils. Experiments with autoclaved soil samples showed that both NO production and NO uptake was mainly due to microbial metabolism.

Microbial production and uptake of nitric oxide in soil

Fluxes of NO from three different soils have been studied by a flow-through system in the laboratory as a function of gas flow rate, of NO mixing ratio, and of incubation conditions. The dependence of net NO fluxes on gas flow rates and on NO mixing ratios could be described by a simple model of simultaneous NO production and NO uptake. By using this model, rates of gross NO production, rate constants of NO uptake, and NO compensation mixing ratios could be determined as function of the soil type and the incubation condition. Gross NO production rates were one to two orders of magnitude larger under anaerobic than under aerobic conditions. NO uptake rate constants, on the other hand, were only 5–8 times larger so that the compensation mixing ratios of NO were in a range of about 1600–2200 ppbv under anaerobic and of about 50–600 ppbv under aerobic conditions. The different soils exhibited similar NO uptake rate constants, but the gross NO production rate and compensation mixing ratio was significantly higher in an acidic (pH 4.7) sandy clay loam than in other less acidic soils. Experiments with autoclaved soil samples showed that both NO production and NO uptake was mainly due to microbial metabolism.

Relationship between nitrate reductase and nitrate uptake in phytoplankton in the Peru upwelling region1,2

Nitrate reductase (NR) activity and 15NO3‒ uptake in phytoplankton were compared under different environmental conditions on two cruises in the upwelling region off Peru. The NR activity and NO3‒ uptake rates responded differently to light and nutrients and the differences led to variations in the uptake; reductase ratio. Analysis of these variations suggests that the re‐equilibration time of the two processes in response to environmental perturbation is an important source of variability. The nitrate uptake system responds faster than the nitrate reductase system. Considering these differences in response time, the basic differences in the two processes, and the differences in their measurement, we conclude that the NR activity measures the current nitrate‐reducing potential, which reflects NO3‒ assimilation before the sampling time, while 15NO3‒ uptake measures NO3‒ assimilation in the 6‐h period following sampling. Thus, considering the sampling time as a point of reference, the former is a measure of the past and the latter is a measure of the future.

Nitrate Uptake, Root and Shoot Growth, and Ion Balance of Soybean Plants during Acclimation to Root-Zone Acidity

The effects of acidity on NO3- absorption by nonnodulated, vegetative soybean (Glycine max [L.] Merrill) plants were examined during a 30-day growth period in flowing solution culture. The acidities of nutrient solutions were maintained at pH 6.1, 5.1, or 4.1 ± 0.1. Root growth rates were reduced for about 20 days by increasing acidity but then recovered to rates which exceeded those at low acidity so that root mass in all treatments was similar after 30 days. In contrast, the uptake rate of NO3- per unit of root mass was enhanced by increased acidity within the first day of exposure to rates that remained constant throughout the treatment period. Total nitrate uptake and shoot growth rates were restricted at higher acidities until about day 20 and thereafter recovered to rates which exceeded those at low acidity in parallel with the recovery in root growth rates. Alterations in total NO3- uptake in response to acidity also were evaluated in relation to changes in uptake of other ions and ionic balance in the plant tissue. As acidity increased, anion uptake was increased relative to cation uptake. Though greater reduction of NO3-, and thus greater generation of internal OH- ions, occurred in plants at higher acidities, tissues contained smaller amounts of organic anions. Acidity of the root-zone, therefore, influenced partitioning of internal OH- generated during NO3- reduction between synthesis of organic anions in the tissue and efflux to the external solution in association with excess anion uptake.