Proportion Of NO3 Research Articles

Coupled isotopic and process‐based modeling of gaseous nitrogen losses from tropical rain forests

Gaseous nitrogen (N) losses remove fixed N from the biosphere and play an important role in regulating Earth's climate system. Current techniques for measuring gaseous N fluxes are still limited, however, and many uncertainties remain. We used the natural isotopes of N, 15N/14N, to constrain process‐based model (DAYCENT, the daily version of CENTURY) estimates of gaseous N emissions from terrestrial ecosystems. The isotope model considers two scenarios. In the first, soil 15N/14N is a linear function of a fraction of gaseous N losses. In the second, underexpression of denitrification's isotope effect is considered, and soil 15N/14N is determined by both the fraction of gaseous losses and the proportion of NO3− consumed locally by denitrification. We examined the coupled process‐ and isotope‐based model along two Hawaiian rain forest gradients which span a range of tropical climates, soil biogeochemical ages, and ecosystem 15N/14N. Under most conditions (mean annual precipitation (MAP) <4050 mm), modeled soil 15N/14N ratios agreed well with measurements (r2 = 0.89), consistent with full expression of denitrification's isotope effect (scenario 1). In very wet sites (MAP ≥ 4050 mm), locally complete NO3− consumption appears to lower the isotopic expression of denitrification at ecosystem levels, resulting in soil 15N/14N ratios that approach those of the N inputs (i.e., scenario 2). Replacing modeled gaseous N emissions with field‐based measures of oxidized N, gas fluxes (NOx + N2O) resulted in consistently lower estimates of soil 15N/14N ratios across the forests. This points to a missing gas N loss term (i.e., N2), inadequate coverage of spatial and temporal heterogeneity by empirical measures, or both. These results demonstrate the potential for soil N isotopes to constrain N gas fluxes at large geographic scales, providing a quantitative tracer of gaseous N emissions from land.

Effects of small dam removal on stream chemistry in southeastern Pennsylvania

AbstractWe examined changes in stream chemistry following the removal of a 2-m-high dam on Manatawny Creek in southeastern Pennsylvania. Our primary objective was to determine the effect of small dam removal on the concentrations and forms of C, N, and P. Dissolved and particulate constituent concentrations were monitored at sites upstream and downstream of the dam and impoundment. Seasonal changes in alkalinity and N and P concentrations were observed before and after dam removal. However, the proportions of NO3− + NO2−, NH4+, and dissolved organic N (DON), and soluble reactive P (SRP) and dissolved organic P (DOP) in the total dissolved pools of N and P did not change seasonally. The dam and dam removal did not influence C, N, or P concentrations and forms (except for NH4+) in this stream. The lack of significant changes probably was a result of the short hydraulic residence time (<1.5 h at base flow), infrequent temperature stratification, and potential C limitation of bacterial activity in the small i...

Influence of Ammonium and Nitrate Nutrition on Plant Growth and Zinc Accumulation by Indian Mustard

ABSTRACT The source of nitrogen (N) used in soil fertility practices affects plant growth, nutrient absorption, and the availability of nutrients. Consequently, the potential of plants to extract zinc (Zn) from soils may be increased by controlling the ratio of NH4 + to NO3 − to maximize growth and Zn accumulation. The objectives of this research were to determine the effects of Zn supply and different molar ratios of NH4 + to NO3 − on growth and Zn accumulation in Indian mustard (Brassica juncea Czern.). In a factorial experiment with solution culture, Indian mustard (accession 182921) was supplied with two concentrations of Zn (0.05 and 4.0 mg L−1) in combination with six N treatments with different molar percentage ratios of NH4 + to NO3 − (0:100, 10:90, 20:80, 30:70, 40:60, and 50:50) for three weeks. Zinc supplied at 0.05 mg Zn L−1 represented a common concentration of Zn in solution culture, whereas 4.0 mg Zn L−1 was excessive for plant nutrition. If the supply of Zn in solution was excessive, plants developed symptoms of foliar chlorosis, which became severe if plants were supplied with 80% of N as NO3 −. Supplying high proportions of NO3 − in the nutrient medium stimulated Zn accumulation, whereas increasing proportions of NH4 + (up to 50% of the total N) enhanced shoot growth. The pH of nutrient solutions generally decreased with increasing proportion of NH4 + in solutions and with increased Zn supply. The Zn phytoextraction potential of Indian mustard was maximized, at about 15 mg Zn plant−1, if plants received 10% of the total N as NH4 + and 90% as NO3 −.

MINERAL NUTRITION OF ARTICHOKE STOCK PLANTS GROWN IN SOILLESS CULTURE

Artichoke plants of 'Romanesco' type [Cynara cardunculus L. var. scolymus (L.) Fiori - cultivar C3] were grown as stock plants under greenhouse conditions for producing disease-free propagation material (offshoots). According to the Systematic Variation method (SV), six nutrient solutions with different proportions of NO3-, SO42-, H2PO4-, K+, Ca2+ and Mg2+ were applied in a randomized complete block design with five replicates. The SV method permitted to calculate the macronutrient proportions, which optimize growth of stock plants (dry weight and leaf number), and offshoot production. In a second experiment, the optimal nutrient formula for offshoot production obtained using the 2001 experiment data was applied at different concentrations (12, 24, 36, 48 and 60 meq/L) in a randomized complete block design with five replicates. The results showed that the highest offshoot production occurred at a macronutrient concentration of 50.2 meq/L.

COMPARISONS OF NITRIFICATION AND DENITRIFICATION IN PRAIRIE AND AGRICULTURALLY INFLUENCED STREAMS

Whole-stream nitrification and denitrification rates were calculated from field incubation studies of representative substrata in Kings Creek and Shane Creek watersheds at the Konza Prairie Biological Station, Kansas, USA. Substrata from a relatively pristine upstream and an agriculturally influenced downstream reach were measured in both watersheds. Rates were scaled to the whole stream by the mass of each substratum in the stream reach. Substrata sampled included epilithon, leaf packs and wood (coarse benthic organic matter, CBOM), filamentous green algae, bryophytes, fine benthic organic matter (FBOM), and suspended particulate organic matter. Upstream sites had significantly lower nitrification and denitrification rates than downstream sites. Nitrification rates were dominated by nitrification associated with epilithon and filamentous green algae. Downstream sites had a higher proportion of nitrification occurring in the water column relative to upstream sites. Whole-stream denitrification was dominated by denitrification associated with FBOM and CBOM and was higher downstream. Water column ammonium (NH4+) and nitrate (NO3−) concentrations were correlated with whole-stream nitrification rates but not whole-stream denitrification rates. Whole-stream nitrification rates were positively correlated with whole-stream denitrification rates, being coupled at the whole-stream level, but not at the substratum level. Relative to the amount of NO3− produced through nitrification, the proportion of NO3− denitrified was 1.4–4.6 times greater in the downstream sites compared to the upstream sites, but the proportion of the in-stream NO3− load denitrified was ∼10 times greater in the upstream sites. These data indicate that changes in stream nitrogen cycling related to increased dissolved inorganic nitrogen concentrations do not result in a large enough increase in denitrification (the stream's capacity to retain nitrogen) to compensate for the increased nitrogen loading. Data also suggest that whole-stream nitrification and denitrification may be decoupled at the reach level by factors that decrease habitat heterogeneity (the variety of substrata types) in stream channels. This indicates that anthropogenic disturbances of small streams, such as channelization and removal of riparian vegetation, would be expected to decrease the capacity of streams to retain nitrogen.

Comparisons of Nitrification and Denitrification in Prairie and Agriculturally Influenced Streams

Whole-stream nitrification and denitrification rates were calculated from field incubation studies of representative substrata in Kings Creek and Shane Creek watersheds at the Konza Prairie Biological Station, Kansas, USA. Substrata from a relatively pristine upstream and an agriculturally influenced downstream reach were measured in both watersheds. Rates were scaled to the whole stream by the mass of each substratum in the stream reach. Substrata sampled included epilithon, leaf packs and wood (coarse benthic organic matter, CBOM), filamentous green algae, bryophytes, fine benthic organic matter (FBOM), and suspended particulate organic matter. Upstream sites had significantly lower nitrification and denitrification rates than downstream sites. Nitrification rates were dominated by nitrification associated with epilithon and filamentous green algae. Downstream sites had a higher proportion of nitrification occurring in the water column relative to upstream sites. Whole-stream denitrification was dominated by denitrification associated with FBOM and CBOM and was higher downstream. Water column ammonium (NH4+) and nitrate (NO3−) concentrations were correlated with whole-stream nitrification rates but not whole-stream denitrification rates. Whole-stream nitrification rates were positively correlated with whole-stream denitrification rates, being coupled at the whole-stream level, but not at the substratum level. Relative to the amount of NO3− produced through nitrification, the proportion of NO3− denitrified was 1.4–4.6 times greater in the downstream sites compared to the upstream sites, but the proportion of the in-stream NO3− load denitrified was ∼10 times greater in the upstream sites. These data indicate that changes in stream nitrogen cycling related to increased dissolved inorganic nitrogen concentrations do not result in a large enough increase in denitrification (the stream's capacity to retain nitrogen) to compensate for the increased nitrogen loading. Data also suggest that whole-stream nitrification and denitrification may be decoupled at the reach level by factors that decrease habitat heterogeneity (the variety of substrata types) in stream channels. This indicates that anthropogenic disturbances of small streams, such as channelization and removal of riparian vegetation, would be expected to decrease the capacity of streams to retain nitrogen.

Nitrate reductase and glutamine synthetase activities in S1 endogamic families of the maize populations Sol da Manhã NF and Catetão

The possibility of improving nitrogen use efficiency in maize was investigated using S1 endogamic families of the populations Sol da Manhã NF and Catetão. A simple 10 X 10 lattice design was adopted and the trials carried out at the experimental field of MITLA AGRÍCOLA LTDA, in Uberlândia, State of Minas Gerais, during the 1994/95 planting season. Based on grain production figures, the three best and three worst performing S1 endogamic families were selected for this study. These were pooled to form four sub-populations denominated NFB, NFR (the best and worst families, respectively, of the Sol da Manhã NF variety), CATB and CATR (the best and worst families, respectively, of the Catetão variety). Each of these sub-populations was evaluated under greenhouse conditions. The experimental design was factorial with treatments arranged in randomized blocks. Sample replicates consisted of pots with four plants. Feeding with modified Hoagland’s nutrient solution began on the seventh day after sowing. The study involved four nitrogen regimes, where varying proportions of NO3- and NH4+ were formulated, such that the nutrient solution contained the following mixtures: 75% NO3- : 25% NH4+; 25% NO3- : 75% NH4+; 50% NO3- : 50% NH4+ (all high N mixtures) and 5% NO3- : 5% NH4+ (low N mixture). Twenty-five days after planting, the activities of the enzymes nitrate reductase and glutamine synthetase (transferase and synthetase assays) were determined for the leaves using the third topmost expanded leaf of the four plants in each pot. The data show that glutamine synthetase (transferase assay) and nitrate reductase activities were efficient in discriminating the S1 endogamic families and could therefore be useful biochemical parameters in breeding programs seeking nitrogen use efficiency.

Model of nitrification and denitrification in marine sediments

Processes involved in the C, N, S, and O cycles in a marine sediment were stimulated for a situation where most organic degradation occured in the top 2 mm and NO3− was not present in the overlying water. The effect of increasing organic loading was examined (degradation of C ? 7 to 107 mmol m−2 d−1). Increasing organic loading had the following results: (1) ? 50% of the dissolved organic nitrogen was lost by diffusion in all treatments; (2) the proportion of NH4++; flux increased, the proportion of nitrification increased slightly and then decreased; and (3) the proportion of NO3− of NO3− efflux.

Effects of osmotic stress (NaCl and polyethylene glycol) on nitrate uptake, translocation, storage and reduction in ryegrass (Lolium perenne L.)

SUMMARYIn order in investigate the effects of osmotic stress on metabolism of NO3− in Lolium perenne L. cv. Réveille, plants were exposed to NaCl or polyethylene glycol 6000 in the culture medium. Four‐week‐old plants were kept in the dark for 36 h in order to decrease nitrate reductase activity (NRA). Afterwards, they were placed in a greenhouse for 27 h under continuous illumination with a nutrient solution containing 1 mM 14NH415NO3. To induce osmotic stress, the solution was supplemented with either NaCl or PEG 6000 to give an osmotic potential of —0·335 MPa in the medium. Osmotic adjustment in PEG treated plants was strongly limited, because PEG could not be absorbed. Over 70% of the osmoregulation in NaCl treated plants resulted from chloride uptake. Compared to control plants, PEG 6000 treatment decreased absorption (by 40%) and reduction (by 60 %) of NO3− in the leaves, leading to NO3− storage in the vacuolar pool. In contrast, addition of NaCl in the medium did not significantly affect either uptake or reduction of NO3−. The proportion of NO3− translocated to the leaves was unaffected by osmotic stress and represented about 76% of consumed NO3−. Nitrate reductase activity, measured in vivo with exogenously supplied NO3−, was not significantly different between treatments. Compared to reduction of p15NO3− in control plants, it appeared that reduction of NO3− in leaves of PEG‐treated plants was not limited by enzyme activity or by the amount of reducing power. Availability of NO3− at the site of reduction therefore seems to be limiting when PEG 6000 is added to the medium.

Nitrogen source effects on Al toxicity in nonmycorrhizal and mycorrhizal pitch pine (Pinus rigida) seedlings. II. Nitrate reduction and NO3− uptake

Nitrogen source utilization, mediated by the ectomycorrhizal symbiont Pisolithus tinctorius, may modulate Al toxicity in pitch pine (Pinus rigida) seedlings. Nitrate reduction, occurring primarily in the roots of pitch pine seedlings, represents a critical metabolic pathway that may be directly sensitive to Al or indirectly affected by changes in NO3− availability associated with Al exposure or mycorrhizal infection. To investigate these possibilities, pitch pine seedlings were grown in sand culture with NO3−, NH4NO3, or NH4+ and exposed to 0 or 200 μM Al for 6 weeks. Foliar N concentrations, root nitrate reductase (NR) activity, and Al inhibition of NR activity were highly dependent on the proportion of NO3− of the nutrient solution. The association of Pisolithus tinctorius with seedling roots reduced both root and foliar NR activity compared with non-inoculated controls, suggesting that NO3− uptake and translocation to foliage was reduced by the symbiont. This was confirmed by using 36ClO3− to measure unidirectional plasma membrane NO3− fluxes. Mycorrhizal root tips absorbed 50% less NO3− than nonmycorrhizal root tips. Preferential use of NH4+ by ectomycorrhizal roots may thus result in reduced movement of Al into root tissue and amelioration of Al toxicity. Key words: Pinus rigida, ectomycorrhizae, aluminum toxicity, nitrogen source.

Particulate emissions from a mid‐latitude prescribed chaparral fire

Smoke aerosol was collected on filters from a helicopter during a 400‐acre (1.62 km2) prescribed chaparral burn in the San Dimas Experimental Forest on December 12, 1986. Hi‐VoI samplers were used to collect particles on both Teflon and glass fiber filters. Scanning electron microscopy of the filters revealed particles that ranged in size from about 0.1 to 100 μm. Many of the large particles (&gt;10 μm) that appeared irregularly shaped at low magnifications were found at higher magnification to be highly agglomerated smaller spheres, often showing signs of partial coalescence. Energy dispersive analysis of X rays (EDAX) revealed carbon, oxygen, magnesium, aluminum, silicon, calcium, and iron as the primary elemental composition of the aerosols. Extractions of aerosol components in water/methanol mixtures, followed by ion Chromatographic analysis, indicated that significant levels of nitrite (NO2−), nitrate (NO3−), sulfate (SO4=), chloride (Cl−), phosphate (PO4≡), oxylate (C2O4=), sodium (Na+), ammonium (NH4+), and potassium (K+) were associated with the particles. The proportions of NO3−, NO2−, PO4≡, Na+, and C2O4 = leached from the aerosol appeared to remain relatively constant in the smoke plume collections. Analysis of soluble NH4 +, Cl−, K +, and SO4 = ions, however, suggested that either possible changes in the nature of the emissions had occurred during different stages of combustion, or that ongoing smoke plume chemistry might have influenced the levels of these ions, or both. The soluble ionic portion of the aerosol was estimated to be about 2% by weight. The first known determinations of phosphate anion from particulates collected in a biomass burn plume are reported.