Uptake Rates Of NO3 Research Articles

Root nitrogen uptake capacity of Chinese fir enhanced by warming and nitrogen addition.

There is a knowledge gap in the effects of climate warming and nitrogen (N) deposition on root N absorption capacity, which limits our ability to predict how climate change alters the N cycling and its consequences for forest productivity especially in subtropical areas where soil N availability is already high. In order to explore the effects and mechanism of warming and the N deposition on root N absorption capacity of Chinese fir (Cunninghamia lanceolata), a subtropical arbuscular mycorrhizal conifer, the fine root 15NH4+ and 15NO3- uptake kinetics at a reference temperature of 20 °C were measured across different seasons in a factorial soil warming (ambient, +5 °C)×N addition (ambient, +40kgNha-1yr-1) experiment. The results showed that (i) compared with the control, warming increased the maximal uptake rate of NH4+ (Vmax,20 °C-NH4+) in summer, while N addition enhanced it in spring and summer; compared with non-warming treatments, warming treatments increased the uptake rate of NO3- at a reference concentration of 100μmol (V100,20 °C-NO3-) in spring. (ii) The analysis of covariance showed that Vmax,20 °C-NH4+ was positively correlated with root mycorrhizal colonization rate (MCR) and V100,20 °C-NO3- was positively correlated with specific root respiration rate (SRR), whereas no N uptake kinetic parameter was correlated with specific root length, root N and non-structural carbon concentrations. Thus, our results demonstrate that warming-increased root NH4+ uptake might be related to warming-increased MCR, whereas warming-increased root NO3- uptake might be related to warming-increased SRR. We conclude that root NH4+ and NO3- uptake capacity of subtropical Chinese fir can be elevated under warming and N deposition, which could improve plantation productivity and mitigate N leaching loss and soil acidification.

Effects of oxygen fertilization on damage reduction in flooded snap bean (Phaseolus vulgaris L.)

Flooding is one of the major abiotic stresses for vegetable production in Florida. Hydroponic and pot trials were conducted with snap bean to evaluate the effects of oxygen fertilization on the biochemical and physiological status of flooded snap bean plants. There were three treatments in the hydroponic trials were: (1) flooded (control), (2) bubble aeration with ambient air, and (3) hydrogen peroxide (H2O2) applied at the beginning of the trial. Plant health was evaluated by determining nitrogen (N) and phosphorus (P) uptake rates. The greenhouse pot trials were used to quantify the effects of three different application rates of solid oxygen fertilizers as calcium peroxide (CaO2) and magnesium peroxide (MgO2). The results showed that plant N and P uptake rates were significantly greater (p < 0.05) with H2O2 than without H2O2. The N uptake rates with H2O2 were like that of those with bubbling. The uptake rate of NH4+ was significantly greater than that of NO3− with the bubbling and H2O2 conditions, but the uptake rate of NO3− was significantly greater than that of NH4+ in the flooding condition. The plant height, leaf greenness, shoot biomass, and yield were all significantly greater with CaO2 or MgO2 than without either solid oxygen fertilizer. The minimum damage of flooded snap bean was found with 2 g CaO2 or 4 g MgO2 per pot. These results indicated that oxygen fertilization may potentially improve yield of flooded snap bean plants.

Seasonal characteristics of new production in the coastal area of Hokkaido, the Okhotsk Sea during the ice-free period

Primary production is divided into new or regenerated production based on nitrate or ammonium. New production leads to a net increase in the phytoplankton abundance. Here, we investigated seasonal variations in phytoplankton uptake rates of NO3 and NH4 to estimate the contribution of new production (f-ratio) in the coastal region of Hokkaido, Okhotsk Sea, during ice-free period. High f-ratios (> 0.7) were observed during the spring bloom period (April and May). Relatively high contributions of over 0.4, which have not been previously reported in oligotrophic regions, were frequently observed in the summer and autumn (June to October), despite oligotrophic conditions. In winter (November and December), contributions were below 0.4, despite the relatively high nitrate concentrations. Contributions of new production to that of primary were high during the spring bloom period, summer, and autumn, while being low in the winter. Despite being a relatively eutrophic season, the low contribution in the winter is important because of a significant increase of phytoplankton in the spring bloom and its increase consumption by associated organisms. This seasonal cycle of new production likely plays an important role in the high productivity of fisheries in the study area.

Aeroponic systems: A unique tool for estimating plant water relations and NO3 uptake in response to salinity stress.

The study of transpiration, water, and nutrient uptake during abiotic stress in the root zone is hindered because of the hidden nature of the root zone. In this study, a modified aeroponic system was used to evaluate whole plant transpiration, nitrate and water uptake in the growth and development of tomato plants in response to salinity. Tomato seedlings were exposed to three levels of salinity (1.5, 4.5, and 9 dSm−1) and three levels of nitrate (1, 4, and 8 mM NO3) in a separate experiments conducted concurrently. Whole plant transpiration, water and nitrate uptake were estimated. Our study revealed that ~30 to 35 days after treatment (DAT), water uptake rate per plant increased from a common initial rate of about 0.05 to 1.1, 0.6, and 0.4 kg/day at 1.5, 4.5, and 9 dSm−1 respectively. The NO3 uptake rates in tomatoes grown in 1 and 4 mM NO3 were 5.5 and 22% respectively, of the uptake of tomatoes grown in 8 mM NO3. The estimation of nitrate uptake and lower sensitivity to salinity stress in the aeroponic showed the effectiveness and cost efficiency of the system in the cultivation of vegetables during abiotic stresses. The novelty of the system described is the continuous estimation of root and nutrient uptake by the whole plant at any given time.

Initial short-term nitrate uptake in juvenile, cultivated Saccharina latissima (Phaeophyceae) of variable nutritional state

Abstract To reach the goal of large-scale seaweed cultivation in Norway, new knowledge concerning commercially important species like the kelp Saccharina latissima is essential. This includes fundamental understanding of physiological mechanisms like nutrient uptake kinetics to better understand its ecological niche and nutritional requirements. The initial short-term nitrate (NO3−) uptake kinetics in cultivated S. latissima juvenile sporophytes were evaluated under nitrogen-saturated and nitrogen-limited conditions. The uptake was measured for concentrations in a gradient from 2 to 18 μM NO3− which is representative of Norwegian coastal waters in the main growth season of winter and early spring. Preconditioning treatments led to internal nitrogen pools (total tissue nitrogen and intracellular nitrate) that were significantly lower for the N-limited than for the N-saturated sporophytes prior to the experiment. Nitrate uptake rates, related to biomass (V) and intracellular nitrogen content (U), were linearly related to the substrate concentrations for both N-limited and N-saturated sporophytes, indicating that S. latissima requires high ambient nitrate concentrations to maintain rapid growth. The sporophytes with deficient internal nitrogen pools exhibited higher uptake rates of NO3− than sporophytes with higher internal pools of nitrogen. Mathematical modelling was used to investigate the temporal development of total tissue nitrogen (QN) based on the nitrogen-specific uptake rates (U) and revealed a near linear response of U to changes in QN. The model also found that a maximum estimated value for QN was only approached after more than 20 days at external NO3- concentrations of 8 μM. These results expand the physiological understanding of cultivated S. latissima and are important for a sustainable upscaling of seaweed farm production.

A comparison of nutrient uptake efficiency and growth rate between different macrophyte growth forms

Aquatic macrophytes grow abundantly in many lowland streams and play a key role in ecosystem functioning, such as nutrient retention. In this study, we performed a microcosm experiment to quantify and compare the contribution of two freshwater macrophyte growth forms to nutrient cycling. We measured and compared inorganic nitrogen (NH4–N and NO3–N) and phosphorus (PO4–P) uptake kinetic parameters (Vmax and Cmin) in 12 submerged and seven amphibious plant species. We tested whether relative growth rate (RGR) was related to high Vmax and low Cmin, and quantified changes in nutrient uptake kinetic in a subset of six out of 19 plants species during the growth season. Uptake rates of NH4–N were higher in submerged compared to amphibious plants, whereas uptake rates of NO3–N were significantly higher in amphibious species; PO4–P uptake kinetics were not significantly different between the two growth forms. There were also significant seasonal differences in Vmax NH4–N rate among both submerged and amphibious species and in Vmax NO3–N among amphibious species. Highest uptake rates were observed in summer for both submerged and amphibious species. Overall, we found that nutrient uptake kinetics differed between the two growth forms within and between seasons. Consequently, the presence of both growth forms should extend the period of nutrient uptake across the year and enhance nutrient uptake within seasons. We conclude that higher functional diversity enhances annual nutrient uptake in streams and that stream restoration efforts should consider increasing the niche space available for both submerged and amphibious species.

Biomitigation of CO2 from flue gas by Scenedesmus obtusiusculus AT-UAM using a hybrid photobioreactor coupled to a biomass recovery stage by electro-coagulation-flotation.

The microalga Scenedesmus obtusiusculus AT-UAM efficiently captured CO2 from two flue gas streams in a hybrid photobioreactor located in a greenhouse. Uptake rates of CO2, NO, and SO2 from a formulated gas stream were 160.7mgL-1day-1, 0.73mgL-1day-1, and 1.56mgL-1day-1, respectively, with removal efficiencies of 100% for all gases. Exhaust gases of a motor generator were also removed with uptake rates of 111.4mgL-1day-1, 0.42mgL-1day-1, and 0.98mgL-1day-1, obtaining removal efficiencies of 77%, 71%, and 53% for CO2, NOx, and SO2, respectively. On average, 61% of the CO2 from both flue gas streams was assimilated as microalgal biomass. The maximum CO2 uptake rate of 182mgL-1day-1 was achieved for formulated flue gas flow rate above 100mLmin-1. The biomass recovery of 88% was achieved using a 20-L electro-coagulation-flotation chamber coupled to a settler with a low specific power consumption of 0.27kWhkg-1. The photobioreactor was operated for almost 7months without contamination of invasive species or a decrease in the activity. It is a very encouraging result for long-term operation in flue gas treatment.

Seasonal shifting in the absorption pattern of alpine species for NO3− and NH4+ on the Tibetan Plateau

Using an 15N labelling method (15N-NH4+ and 15N-NO3−), we conducted a time series experiment of N absorption for two common plant species (Stipa purpurea and Artemisia nanschanica) in three seasons (summer, late autumn, and early spring) in a semi-arid alpine steppe ecosystem on the Tibetan Plateau. The soil NO3− content was significantly higher than the exchangeable NH4+ content in summer, whereas exchangeable NH4+ was the dominant inorganic form of N during the cold seasons (late autumn and early spring). Both S. purpurea and A. nanschanica showed a preference for NO3− in summer. The uptake rates of NO3− ranged from 1.09 to 3.94 μg 15N g−1 DW root h−1 for S. purpurea and from 2.85 to 7.82 μg 15N g−1 DW root h−1 for A. nanschanica. In contrast, both species showed a clear preference for NH4+ during the late autumn and early spring, which was strongly dependent on snowfall events. The uptake rate of NH4+ ranged from 0.33 to 4.25 μg 15N g−1 DW root h−1 for S. purpurea and from 0.67 to 9.05 μg 15N g−1 DW root h−1 for A. nanschanica. We also observed that 15N recovery was mainly retained in the roots with a smaller proportion of 15N stored in the shoots across all seasons. The seasonal shift in the pattern of N absorption may be influenced by changes in the ratios of soil exchangeable NH4+ to NO3− in the different seasons. This finding offers valuable insights into the nutrient acquisition strategies of alpine plants and provides an important mechanism for the temporal pattern of N utilisation by plants in alpine environments.

Seasonality of Phosphorus and Nitrate Retention in Riparian Buffers.

Measurement of the retention of dissolved nutrients in riparian areas with snowmelt runoff are much less common than for rainfall runoff, but low rates of uptake or the release of nutrients with snowmelt have been attributed to frozen soils, lower biotic uptake, and release of nutrients from senesced vegetation. In the research presented here, we evaluate whether the potential for uptake of dissolved reactive phosphorus (DRP) and NO differ significantly between snowmelt and summer seasons with flow through 13 riparian buffers downstream of cropland in Manitoba, Canada. Flow-through buffers in small channels are typical in this landscape, and pulsed releases of a conservative tracer and dissolved nutrients were used to measure uptake rates. Although mean uptake rates of NO were higher in summer than for snowmelt, responses varied widely. Aerial uptake rate of DRP showed a significant negative relationships with soil Olsen-P ( = 0.54, < 0.001) and a P saturation index ( = 0.48, < 0.001) across both seasons. Biological processes may be of greater importance for NO retention, but DRP retention appears to be driven by adsorption-desorption regardless of season. Olsen-P is identified as a good indicator of potential for release or retention of DRP in riparian buffers with fine-textured calcareous soils, for both snowmelt and summer seasons. Soil testing may be a good tool to aid in the siting of new buffers and to track the effectiveness of management interventions to remove P from riparian areas, such as harvest of vegetation.

Heterotrophic Bacteria Show Weak Competition for Nitrogen in Mediterranean Coastal Waters (Thau Lagoon) in Autumn.

The importance of heterotrophic bacteria relative to phytoplankton in the uptake of ammonium and nitrate was studied in Mediterranean coastal waters (Thau Lagoon) during autumn, when the Mediterranean Sea received the greatest allochthonous nutrient loads. Specific inhibitors and size-fractionation methods were used in combination with isotopic (15)N tracers. NO3 (-) and NH4 (+) uptake was dominated by phytoplankton (60 % on average) during the study period, which included a flood event. Despite lower biomass specific NH4 (+) and NO3 uptake rates, free-living heterotrophic bacteria contributed significantly (>30 %) to total microbial NH4 (+) and NO3 (-) uptake rates in low chlorophyll waters. Under these conditions, heterotrophic bacteria may be responsible for more than 50 % of primary production, using very little freshly produced phytoplankton exudates. In low chlorophyll coastal waters as reported during the present 3-month study, the heterotrophic bacteria seemed to depend to a greater extent on allochthonous N and C substrates than on autochthonous substrates derived from phytoplankton.

Plant and microbial uptake of nitrogen and phosphorus affected by drought using 15N and 32P tracers

Competition for nutrients between plants and microbes is an important determinant for plant growth, biodiversity and carbon cycling. Perturbations such as drought affect the availability of nitrogen (N) and phosphorus (P), and may cause shifts in uptake of N and P between plants and microbes. Competitiveness for these nutrients may depend on how flexible plants and microbes are in taking up N and P. We used a novel dual isotope labelling technique (15N and 32P) to assess short-term uptake of N and P by plants and microbes affected by drought in two different plant–soil systems. Mesocosms were extracted from two grassland sites differing in soil nutrient availability and plant species. Half of the mesocosms were subjected to drought one week prior to injection of 15N (as KNO3) and 32P (as H3PO4) tracers. Uptake rates of NO3− and P in plants and microbes were estimated based on average source pool enrichment during the labelling period and on plant and microbial recovery of 15N and 32P measured after 4 days of labelling. Overall competition for N and P was reduced with drought as less NO3− and P was taken up in plants and microbes. However, plant uptake of NO3− was more sensitive to drought than microbial NO3− uptake, while microbial P uptake was more sensitive than plant P uptake. These different sensitivities to drought by plants and microbes may decouple the N and P cycle with increased drought conditions.

Nitrogen uptake and regeneration (ammonium regeneration, nitrification and photoproduction) in waters of the West Florida Shelf prone to blooms of Karenia brevis

The West Florida Shelf (WFS) encompasses a range of environments from inshore estuarine to offshore oligotrophic waters, which are frequently the site of large and persistent blooms of the toxic dinoflagellate, Karenia brevis. The goals of this study were to characterize the nitrogen (N) nutrition of plankton across the range of environmental conditions on the WFS, to quantify the percentage of the plankton N demand met through in situ N regeneration, and to determine whether planktonic N nutrition changes when high concentrations of Karenia are present. In the fall of 2007, 2008, and 2009 we measured ambient nutrient concentrations and used stable isotope techniques to measure rates of primary production and uptake rates of inorganic N (ammonium, NH4+, and nitrate, NO3−), and organic N and carbon (C; urea and amino acids, AA) in estuarine, coastal, and offshore waters, as well as coastal sites with Karenia blooms present. In parallel, we also measured rates of in situ N regeneration – NH4+ regeneration, nitrification, and photoproduction of NH4+, nitrite and AA. Based on microscope observations, ancillary measurements, and previous monitoring history, Karenia blooms sampled represented three bloom stages – initiation in 2008, maintenance in 2007, and late maintenance/stationary phase in 2009. Nutrient concentrations were highest at estuarine sampling sites and lowest at offshore sites. Uptake of NH4+ and NO3− provided the largest contribution to N nutrition at all sites. At the non-Karenia sites, in situ rates of NH4+ regeneration and nitrification were generally sufficient to supply these substrates equal to the rates at which they were taken up. At Karenia sites, NO3− was the most important N substrate during the initiation phase, while NH4+ was the most important N form used during bloom maintenance and stationary phases. Rates of NH4+ regeneration were high but insufficient (85±36% of uptake) to support the measured NH4+ uptake at all the Karenia sites although nitrification rates far exceeded uptake rates of NO3−. Taken together our results support the “no smoking gun” nutrient hypothesis that there is no single nutrient source or strategy that can explain Karenia's frequent dominance in the waters where it occurs. Consistent with other papers in this volume, our results indicate that Karenia can utilize an array of inorganic and organic N forms from a number of N sources.

Effect of nitrate fertilization of gametophytes of the kelp Undaria pinnatifida on growth and maturation of the sporophytes cultivated in Matsushima Bay, northern Honshu, Japan

In northern Japan, the early production of high-quality specimens of kelps Undaria pinnatifida prior to the outbreak of pinhole disease is needed. To address this need, we tested the effect of nitrate fertilization of gametophytes on the growth and maturation of sporophytes using experimental and control gametophytes derived from sporophytes cultivated in Matsushima Bay, northern Honshu, Japan. From mid-August to October 2008, experimental gametophytes were cultured on a rope indoors at a nitrate concentration of 1 mg/L at the optimal seawater temperature of 20 °C, whereas control gametophytes were cultured without the addition of nitrate in normal seawater at an average temperature of 23.5 °C during this period in the past 30 years. Next, the seedlings were cultivated in Matsushima Bay until March 2009. For the experimental kelps, the total length, stipe length, stipe width, sporophyll length, sporophyll width, and dry weight of the blade, midrib, and sporophyll increased significantly from December to January compared to those of control kelps. Matured sporophylls of the experimental kelps were more than those of the control kelps from early December to late January. Significant higher photosynthesis occurred at seawater temperatures of 10 and 15 °C, as well as higher uptake rates of NO3–N of the experimental kelps in December and January. These results show that nitrate fertilization of the gametophytes makes it possible to harvest the high-priced blade, midrib, and sporophyll in January, which is earlier than the traditional harvest date.

Interactions between uptake of amino acids and inorganic nitrogen in wheat plants

Abstract. Soil-borne amino acids may constitute a source of nitrogen (N) for plants in various terrestrial ecosystems but their importance for total N nutrition is unclear, particularly in nutrient-rich arable soils. One reason for this uncertainty is lack of information on how the absorption of amino acids by plant roots is affected by the simultaneous presence of inorganic N forms. The objective of the present study was to study absorption of glycine (Gly) and glutamine (Gln) by wheat roots and their interactions with nitrate (NO3−) and ammonium (NH4+) during uptake. The underlying hypothesis was that amino acids, when present in nutrient solution together with inorganic N, may lead to down-regulation of the inorganic N uptake, thereby resulting in similar total N uptake rates. Amino acids were enriched with double-labelled 15N and 13C, while NO3− and NH4+ acquisition was determined by their rate of removal from the nutrient solution surrounding the roots. The uptake rates of NO3− and NH4+ did not differ from each other and were generally about twice as high as the uptake rate of organic N when the different N forms were supplied separately in concentrations of 2 mM. Nevertheless, replacement of 50% of the inorganic N with organic N was able to restore the N uptake to the same level as that in the presence of only inorganic N. Co-provision of NO3− did not affect glycine uptake, while the presence of glycine down-regulated NO3− uptake. The ratio between 13C and 15N were lower in shoots than in roots and also lower than the theoretical values, reflecting higher C losses via respiratory processes compared to N losses. It is concluded that organic N can constitute a significant N-source for wheat plants and that there is an interaction between the uptake of inorganic and organic N.

Assimilation and regeneration of inorganic nitrogen in a coastal upwelling system: ammonium and nitrate utilization

The main processes involved in nitrogen cycling (as NO3 � and NH4 + assimilation and their re- generation) were studied using N-tracer experiments in the coastal upwelling system off central Chile (36°S). The study area shows seasonal surface fertil- ization and the development of subsurface hypoxia in austral spring and summer. The rates of NO3 � uptake during active upwelling were 5 times higher than in non-upwelling seasons. Uptake of NH4 + was almost half that of NO3 � uptake rates during upwelling peri- ods, and similar to NO3 � uptake rates in the absence of upwelling. Nitrification experiments showed higher rates during active, compared to non-active, upwelling seasons. NH4 + oxidation was coupled with NO2 � oxi- dation in near bottom (suboxic) waters, while in the oxycline (hypoxic water), total fluxes of NO3 � regener- ation via nitrification resulted from higher activity of NO2 � oxidation compared to NH4 + oxidation. On the other hand, archaeal NH4 + oxidation had the potential for processing a large fraction of NH4 + and could therefore co-occur with bacterial NO2 � oxidation. NH4 + utilization in this coastal up welling is thus in the same range as NO3 � assimilation. NH4 + oxidation is af- fected by oxygen concentration in the water column, leading to occasional decoupling of NH4 + and NO2 � oxidation, particularly at the oxycline. This study gives preliminary evidence of the importance of archaeal- bacterial interactions in the nitrification process and highlights the role of ammonium in fueling annual primary production in coastal upwelling systems.

Nitrogen uptake kinetics of Prymnesium parvum (Haptophyte)

The uptake rates of different nitrogen (N) forms (NO 3 −, urea, and the amino acids glycine and glutamic acid) by N-deficient, laboratory-grown cells of the mixotrophic haptophyte, Prymnesium parvum, were measured and the preference by the cells for the different forms determined. Cellular N uptake rates ( ρ cell, fmol N cell −1 h −1) were measured using 15N-labeled N substrates. P. parvum showed high preference for the tested amino acids, in particular glutamic acid, over urea and NO 3 − under the culture nutrient conditions. However, extrapolating these rates to Baltic Seawater summer conditions, P. parvum would be expected to show higher uptake rates of NO 3 − and the amino acids relative to urea because of the difference in average concentrations of these substrates. A high uptake rate of glutamic acid at low substrate concentrations suggests that this substrate is likely used through extracellular enzymes. Nitrate, urea and glycine, on the other hand, showed a non-saturating uptake over the tested substrate concentration (1–40 μM-N for NO 3 − and urea, 0.5–10 μM-N for glycine), indicating slower membrane-transport rates for these substrates.

Bioaccumulation kinetics of polybrominated diphenyl ethers from estuarine sediments to the marine polychaete, Nereis virens

Polybrominated diphenyl ethers (PBDEs) are flame-retardant chemicals that have become ubiquitous environmental contaminants. Polybrominated diphenyl ether no-uptake rates from estuarine or marine sediments to deposit-feeding organisms have not yet been reported. In the present study, the marine polychaete worm Nereis virens was exposed to field-contaminated and spiked sediments containing the penta- and deca-BDE commercial mixtures in a 28-d experiment to characterize the relative bioavailability of PBDE congeners from estuarine sediments. A time series sampling regimen was conducted to estimate uptake rate constants. In both field-collected and laboratory-spiked sediment exposures, worms selectively accumulated congeners in the penta-BDE mixture over BDE 209 and other components of the deca-BDE mixture, supporting the prevalence of these congeners in higher trophic level species. Brominated diphenyl ether 209 was not bioavailable to N. virens from field sediment and was only minimally detected in worms exposed to spiked sediments in which bioavailability was maximized. Chemical hydrophobicity was not a good predictor of bioavailability for congeners in the penta-BDE mixture. Direct comparison of bioavailability from the spiked and field sediments for the predominant congeners in the penta-BDE mixture was confounded by the considerable difference in exposure concentration between treatments. Biota-sediment accumulation factors (BSAFs) for N. virens after 28 d of exposure to the field sediment were lower than the BSAFs for Nereis succinea collected from the field site, indicating that 28-d bioaccumulation tests using N. virens may underestimate the in situ concentration of PBDEs in deposit-feeding species. The bioavailability of PBDEs to N. virens indicates that these chemicals can be remobilized from estuarine sediments and transferred to aquatic food webs.

Nitrogen nutrition of Canna indica: Effects of ammonium versus nitrate on growth, biomass allocation, photosynthesis, nitrate reductase activity and N uptake rates

The effects of inorganic nitrogen (N) source (NH 4 +, NO 3 − or both) on growth, biomass allocation, photosynthesis, N uptake rate, nitrate reductase activity and mineral composition of Canna indica were studied in hydroponic culture. The relative growth rates (0.05–0.06 g g −1 d −1), biomass allocation and plant morphology of C. indica were indifferent to N nutrition. However, NH 4 + fed plants had higher concentrations of N in the tissues, lower concentrations of mineral cations and higher contents of chlorophylls in the leaves compared to NO 3 − fed plants suggesting a slight advantage of NH 4 + nutrition. The NO 3 − fed plants had lower light-saturated rates of photosynthesis (22.5 μmol m −2 s −1) than NH 4 + and NH 4 +/NO 3 − fed plants (24.4–25.6 μmol m −2 s −1) when expressed per unit leaf area, but similar rates when expressed on a chlorophyll basis. Maximum uptake rates ( V max) of NO 3 − did not differ between treatments (24–35 μmol N g −1 root DW h −1), but V max for NH 4 + was highest in NH 4 + fed plants (81 μmol N g −1 root DW h −1), intermediate in the NH 4NO 3 fed plants (52 μmol N g −1 root DW h −1), and lowest in the NO 3 − fed plants (28 μmol N g −1 root DW h −1). Nitrate reductase activity (NRA) was highest in leaves and was induced by NO 3 − in the culture solutions corresponding to the pattern seen in fast growing terrestrial species. Plants fed with only NO 3 − had high NRA (22 and 8 μmol NO 2 − g −1 DW h −1 in leaves and roots, respectively) whereas NRA in NH 4 + fed plants was close to zero. Plants supplied with both forms of N had intermediate NRA suggesting that C. indica takes up and assimilate NO 3 − in the presence of NH 4 +. Our results show that C. indica is relatively indifferent to inorganic N source, which together with its high growth rate contributes to explain the occurrence of this species in flooded wetland soils as well as on terrestrial soils. Furthermore, it is concluded that C. indica is suitable for use in different types of constructed wetlands.

THE RELATIVE IMPORTANCE OF WATER MOTION ON NITROGEN UPTAKE BY THE SUBTIDAL MACROALGA ADAMSIELLA CHAUVINII (RHODOPHYTA) IN WINTER AND SUMMER(1).

The influence of seawater velocity (1.5-12 cm · s(-1) ) on inorganic nitrogen (N) uptake by the soft-sediment perennial macroalga Adamsiella chauvinii (Harv.) L. E. Phillips et W. A. Nelson (Rhodophyta) was determined seasonally by measuring uptake rate in a laboratory flume. Regardless of N tissue content, water velocity had no influence on NO3 (-) uptake in either winter or summer, indicating that NO3 (-) -uptake rate was biologically limited. However, when thalli were N limited, increasing water velocity increased NH4 (+) uptake, suggesting that mass-transfer limitation of NH4 (+) is likely during summer for natural populations. Uptake kinetics (Vmax , Ks ) were similar among three populations of A.chauvinii at sites with different mean flow speeds; however, uptake rates of NO3 (-) and NH4 (+) were lower in summer (when N status was generally low) than in winter. Our results highlight how N uptake can be affected by seasonal changes in the physiology of a macroalga and that further investigation of N uptake of different macroalgae (red, brown, and green) during different seasons is important in determining the relative influence of water velocity on nutrient uptake.

Superoxide counteracts low-density lipoprotein-induced human aortic smooth muscle cell proliferation

Previously, we demonstrated that the level of intracellular O(2)(-) is increased by low-density lipoprotein (LDL) in human aortic smooth muscle cells (HASMCs). The exact role of O(2)(-) in the LDL-induced proliferation of HASMCs, however, has not been determined. In this study, we found that the increase in the concentrations of intracellular O(2)(-) induced by native and oxidized LDL increased SMC-nitric oxide (NO) uptake rate. Moreover, the treatment of HASMCs with diethyldithiocarbamate (DETC), a superoxide dismutase inhibitor, significantly increased NO uptake rate owing to the increase in intracellular O(2)(-) concentrations. Although native and oxidized LDL decreased soluble guanylyl cyclase (sGC) protein content, they still caused a net increase in cyclic GMP production in HASMCs. In addition, when cyclic GMP production was normalized by sGC protein content and NO uptake rate, it was found to be positively dependent on the level of intracellular H(2)O(2). Finally, we simulated cell proliferation stimulated by native and oxidized LDL as a linear function of intracellular O(2)(-) and H(2)O(2) concentrations, demonstrating that O(2)(-) negatively modulated the native and oxidized LDL-stimulated HASMC proliferation through the increase in NO uptake rate.