Differential contributions of NO3 -/NH4 + to nitrogen use in response to a variable inorganic nitrogen supply in plantlets of two Brassicaceae species in vitro.
ABSTRACT: Background:The primary sources of nitrogen for plants have been suggested to be nitrate (NO3 -) and ammonium (NH4 +). However, when both nitrate and ammonium are simultaneously available to plants, it is very difficult to differentially quantify NO3 -/NH4 + utilization in culture media or soil. Consequently, the contribution of NO3 -/NH4 + to total inorganic nitrogen assimilation cannot be determined. Results:We developed a method called the bidirectional stable nitrogen isotope tracer to differentially quantify the nitrate and ammonium utilization by Orychophragmus violaceus (Ov) and Brassica napus (Bn) plantlets in vitro. The utilization efficiency of nitrate was markedly lower than the utilization efficiency of ammonium for plantlets of both Ov and Bn. In both Ov and Bn, the proportion of NO3 -/NH4 + utilization did not show a linear relationship with inorganic nitrogen supply. The Ov plantlets assimilated more nitrate than the Bn plantlets at the lowest inorganic nitrogen concentration. Conclusions:Quantifying the utilization of nitrate and ammonium can reveal the differences in nitrate and ammonium assimilation among plants at different inorganic nitrogen supply levels and provide an alternate way to conveniently optimize the supply of inorganic nitrogen in culture media.
Project description:The marine macrophyte Ulva prolifera is the dominant green-tide-forming seaweed in the southern Yellow Sea, China. Here we assessed, in the laboratory, the growth rate and nutrient uptake responses of U. prolifera to different nutrient treatments. The growth rates were enhanced in incubations with added organic and inorganic nitrogen [i.e. nitrate (NO3(-)), ammonium (NH4(+)), urea and glycine] and phosphorus [i.e. phosphate (PO4(3-)), adenosine triphosphate (ATP) and glucose 6-phosphate (G-6-P)], relative to the control. The relative growth rates of U. prolifera were higher when enriched with dissolved organic nitrogen (urea and glycine) and phosphorus (ATP and G-6-P) than inorganic nitrogen (NO3(-) and NH4(+)) and phosphorus (PO4(3-)). In contrast, the affinity was higher for inorganic than organic nutrients. Field data in the southern Yellow Sea showed significant inverse correlations between macroalgal biomass and dissolved organic nutrients. Our laboratory and field results indicated that organic nutrients such as urea, glycine and ATP, may contribute to the development of macroalgal blooms in the southern Yellow Sea.
Project description:In freshwaters, algal species are exposed to different inorganic nitrogen (Ni) sources whose incorporation varies in biochemical energy demand. We hypothesized that due to the lesser energy requirement of ammonium ( NH4+ )-use, in contrast to nitrate ( NO3- )-use, more energy remains for other metabolic processes, especially under CO2- and phosphorus (Pi) limiting conditions. Therefore, we tested differences in cell characteristics of the green alga Chlamydomonas acidophila grown on NH4+ or NO3- under covariation of CO2 and Pi-supply in order to determine limitations, in a full-factorial design. As expected, results revealed higher carbon fixation rates for NH4+ -grown cells compared to growth with NO3- under low CO2 conditions. NO3- -grown cells accumulated more of the nine analyzed amino acids, especially under Pi-limited conditions, compared to cells provided with NH4+ . This is probably due to a slower protein synthesis in cells provided with NO3- . In contrast to our expectations, compared to NH4+ -grown cells NO3- -grown cells had higher photosynthetic efficiency under Pi-limitation. In conclusion, growth on the Ni-source NH4+ did not result in a clearly enhanced Ci-assimilation, as it was highly dependent on Pi and CO2 conditions (replete or limited). Results are potentially connected to the fact that C. acidophila is able to use only CO2 as its inorganic carbon (Ci) source.
Project description:Plants mainly acquire N from the soil in the form of nitrate (NO3 -) or ammonium (NH4 +). Ammonium-based nutrition is gaining interest because it helps to avoid the environmental pollution associated with nitrate fertilization. However, in general, plants prefer NO3 - and indeed, when growing only with NH4 + they can encounter so-called ammonium stress. Since Brachypodium distachyon is a useful model species for the study of monocot physiology and genetics, we chose it to characterize performance under ammonium nutrition. Brachypodium distachyon Bd21 plants were grown hydroponically in 1 or 2.5 mM NO3 - or NH4 +. Nitrogen and carbon metabolism associated with NH4 + assimilation was evaluated in terms of tissue contents of NO3 -, NH4 +, K, Mg, Ca, amino acids and organic acids together with tricarboxylic acid (TCA) cycle and NH4 +-assimilating enzyme activities and RNA transcript levels. The roots behaved as a physiological barrier preventing NH4 + translocation to aerial parts, as indicated by a sizeable accumulation of NH4 +, Asn and Gln in the roots. A continuing high NH4 + assimilation rate was made possible by a tuning of the TCA cycle and its associated anaplerotic pathways to match 2-oxoglutarate and oxaloacetate demand for Gln and Asn synthesis. These results show B. distachyon to be a highly suitable tool for the study of the physiological, molecular and genetic basis of ammonium nutrition in cereals.
Project description:Japonica rice is widely planted in north-eastern China because of its superior food quality and stable grain yields. Nitrogen (N) is an essential element for rice growth, and development and its availability directly impacts on rice yields. The knowledge of N uptake and its utilization characteristics in japonica are thus important areas of research. Three japonica rice cultivars, SN265, SN1401, and SN9816, which are planted across large areas of north-eastern China, were used here to evaluate the uptake and utilization along the life cycle of both ammonium (NH4+) and nitrate (NO3-) in hydroponically grown plants. The plants were grown in one of three different solutions with varying NH4+ : NO3- ratios: 1:0, 0:1, and 1:1 (The total N content was 40 mg L-1 for each treatment). At the tillering stage, when only NO3- was provided, lower rates of N uptake and enzyme activities of three rice plants resulted in reduced tiller numbers. During the reproductive stage, the NH4+ and (NH4+) uptake rates in SN1401 were consistently maintained at high levels, whereas the rates in SN265 and SN9816 were significantly lower, across all three treatments. At the booting stage, when only NO3- was provided, SN1401 plants had significantly higher expression levels of OsNRT2.1 and OsNRT2.2, higher activity of nitrate reductase in the roots, and higher activity levels of glutamine synthetase and glutamate synthase in the leaves, compared with the SN265 and SN9816 plants. The higher enzyme activity was beneficial to the secondary assimilation of N, which ultimately promoted panicle development in SN1401. Consequently, the grain yield per plant of SN1401 was the highest with solutions of both NH4+ and NO3- . These results indicate that selecting a rice cultivar with higher utilization of NO3- is beneficial for increasing the number of grains per panicle, grain yield, and N use efficiency.
Project description:Nitrate (NO3-) and ammonium (NH4+) are the main inorganic nitrogen (N) sources absorbed by oilseed rape, a plant that exhibits genotypic differences in N efficiency. In our previous study, the biomass, N accumulation, and root architecture of two oilseed rape cultivars, Xiangyou 15 (high N efficiency, denoted "15") and 814 (low N efficiency, denoted "814"), were inhibited under NH4+ nutrition, though both cultivars grew normally under NO3- nutrition. To gain insight into the underlying molecular mechanisms, transcriptomic changes were investigated in the roots of 15 and 814 plants subjected to nitrogen-free (control, CK), NO3- (NT), and NH4+ (AT) treatments at the seedling stage. A total of 14,355 differentially expressed genes (DEGs) were identified. Among the enriched Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway categories of these DEGs, carbohydrate metabolism, lipid metabolism, protein metabolism, and cell wall biogenesis were inhibited by AT treatment. Interestingly, DEGs such as N transporters, genes involved in N assimilation and CESA genes related to cellulose synthase were also mostly downregulated in the AT treatment group. This downregulation of genes related to crucial metabolic pathways resulted in inhibition of oilseed rape growth after AT treatment.
Project description:We examined nitrate-dependent Fe(2+) oxidation mediated by anaerobic ammonium oxidation (anammox) bacteria. Enrichment cultures of "Candidatus Brocadia sinica" anaerobically oxidized Fe(2+) and reduced NO3(-) to nitrogen gas at rates of 3.7 ± 0.2 and 1.3 ± 0.1 (mean ± standard deviation [SD]) nmol mg protein(-1) min(-1), respectively (37°C and pH 7.3). This nitrate reduction rate is an order of magnitude lower than the anammox activity of "Ca. Brocadia sinica" (10 to 75 nmol NH4(+) mg protein(-1) min(-1)). A (15)N tracer experiment demonstrated that coupling of nitrate-dependent Fe(2+) oxidation and the anammox reaction was responsible for producing nitrogen gas from NO3(-) by "Ca. Brocadia sinica." The activities of nitrate-dependent Fe(2+) oxidation were dependent on temperature and pH, and the highest activities were seen at temperatures of 30 to 45°C and pHs ranging from 5.9 to 9.8. The mean half-saturation constant for NO3(-) ± SD of "Ca. Brocadia sinica" was determined to be 51 ± 21 ?M. Nitrate-dependent Fe(2+) oxidation was further demonstrated by another anammox bacterium, "Candidatus Scalindua sp.," whose rates of Fe(2+) oxidation and NO3(-) reduction were 4.7 ± 0.59 and 1.45 ± 0.05 nmol mg protein(-1) min(-1), respectively (20°C and pH 7.3). Co-occurrence of nitrate-dependent Fe(2+) oxidation and the anammox reaction decreased the molar ratios of consumed NO2(-) to consumed NH4(+) (?NO2(-)/?NH4(+)) and produced NO3(-) to consumed NH4(+) (?NO3(-)/?NH4(+)). These reactions are preferable to the application of anammox processes for wastewater treatment.
Project description:Plants have evolved different strategies to utilize various forms of nitrogen (N) from the environment. While regulation of plant growth and development in response to application of inorganic N forms has been characterized, our knowledge about the effect on cell wall structure and composition is quite limited. In this study, we analysed cell walls of Brachypodium distachyon supplied with three types of inorganic N (NH4NO3, NO3-, or NH4+). Cell wall profiles showed distinct alterations in both the quantity and structures of individual polymers. Nitrate stimulated cellulose, but inhibited lignin deposition at the heading growth stage. On the other hand, ammonium supply resulted in higher concentration of mixed linkage glucans. In addition, the chemical structure of pectins and hemicelluloses was strongly influenced by the form of N. Supply of only NO3- led to alteration in xylan substitution and to lower esterification of homogalacturonan. We conclude that the physiological response to absorption of different inorganic N forms includes pleotropic remodelling of type II cell walls.
Project description:Six species of phytoplankton recently isolated from upper San Francisco Bay were tested for their sensitivity to growth inhibition by ammonium (NH4+ ), and for differences in growth rates according to inorganic nitrogen (N) growth source. The quantum yield of photosystem II (Fv /Fm ) was a sensitive indicator of NH4+ toxicity, manifested by a suppression of Fv /Fm in a dose-dependent manner. Two chlorophytes were the least sensitive to NH4+ inhibition, at concentrations of >3,000 ?moles NH4+ · L-1 , followed by two estuarine diatoms that were sensitive at concentrations >1,000 ?moles NH4+ · L-1 , followed lastly by two freshwater diatoms that were sensitive at concentrations between 200 and 500 ?moles NH4+ · L-1 . At non-inhibiting concentrations of NH4+ , the freshwater diatom species grew fastest, followed by the estuarine diatoms, while the chlorophytes grew slowest. Variations in growth rates with N source did not follow taxonomic divisions. Of the two chlorophytes, one grew significantly faster on nitrate (NO3- ), whereas the other grew significantly faster on NH4+ . All four diatoms tested grew faster on NH4+ compared with NO3- . We showed that in cases where growth rates were faster on NH4+ than they were on NO3- , the difference was not larger for chlorophytes compared with diatoms. This holds true for comparisons across a number of culture investigations suggesting that diatoms as a group will not be at a competitive disadvantage under natural conditions when NH4+ dominates the total N pool and they will also not have a growth advantage when NO3- is dominant, as long as N concentrations are sufficient.
Project description:In many oceanic regions, growth of phytoplankton is nitrogen-limited because fixation of N2 cannot make up for the removal of fixed inorganic nitrogen (NH4+, NO2-, and NO3-) by anaerobic microbial processes. Globally, 30-50% of the total nitrogen loss occurs in oxygen-minimum zones (OMZs) and is commonly attributed to denitrification (reduction of nitrate to N2 by heterotrophic bacteria). Here, we show that instead, the anammox process (the anaerobic oxidation of ammonium by nitrite to yield N2) is mainly responsible for nitrogen loss in the OMZ waters of one of the most productive regions of the world ocean, the Benguela upwelling system. Our in situ experiments indicate that nitrate is not directly converted to N2 by heterotrophic denitrification in the suboxic zone. In the Benguela system, nutrient profiles, anammox rates, abundances of anammox cells, and specific biomarker lipids indicate that anammox bacteria are responsible for massive losses of fixed nitrogen. We have identified and directly linked anammox bacteria to the removal of fixed inorganic nitrogen in the OMZ waters of an open-ocean setting. We hypothesize that anammox could also be responsible for substantial nitrogen loss from other OMZ waters of the ocean.
Project description:Stormwater runoff is a leading cause of nitrogen (N) transport to water bodies and hence one means of water quality deterioration. Stormwater runoff was monitored in an urban residential catchment (drainage area: 3.89 hectares) in Florida, United States to investigate the concentrations, forms, and sources of N. Runoff samples were collected over 22 storm events (May to September 2016) at the end of a stormwater pipe that delivers runoff from the catchment to the stormwater pond. Various N forms such as ammonium (NH4-N), nitrate (NOx-N), dissolved organic nitrogen (DON), and particulate organic nitrogen (PON) were determined and isotopic characterization tools were used to infer sources of NO3-N and PON in collected runoff samples. The DON was the dominant N form in runoff (47%) followed by PON (22%), NOx-N (17%), and NH4-N (14%). Three N forms (NOx-N, NH4-N, and PON) were positively correlated with total rainfall and antecedent dry period, suggesting longer dry periods and higher rainfall amounts are significant drivers for transport of these N forms. Whereas DON was positively correlated to only rainfall intensity indicating that higher intensity rain may flush out DON from soils and cause leaching of DON from particulates present in the residential catchment. We discovered, using stable isotopes of NO3-, a shifting pattern of NO3- sources from atmospheric deposition to inorganic N fertilizers in events with higher and longer duration of rainfall. The stable isotopes of PON confirmed that plant material (oak detritus, grass clippings) were the primary sources of PON in stormwater runoff. Our results demonstrate that practices targeting both inorganic and organic N are needed to control N transport from residential catchments to receiving waters.