mM Of NO3 Research Articles

Influence of Nitrogen Supply on Growth, Antioxidant Capacity and Cadmium Absorption of Kenaf (Hibiscus cannabinus L.) Seedlings

Kenaf (Hibiscus cannabinus L.) is considered suitable for the remediation of cadmium (Cd)-contaminated farmlands, because of its large biomass and resistance to Cd stress. The addition of nitrogen (N) fertilizer is an important measure used to increase crop yields, and it may also affect Cd accumulation in plants. To clarify the effects of different forms and concentrations of N on plant growth and Cd absorption in kenaf, a hydroponic experiment was conducted using three N forms (NH4+–N, NO3−–N and urea–N) at four concentrations (0, 2, 4 and 8 mM, 0 mM as control) under Cd stress (30 μM). The plant growth, the antioxidant enzyme activity and the Cd contents of various parts of the kenaf seedlings were measured. The results showed that the N form had the greatest impact on the growth of the kenaf and the absorption and transport of the Cd, followed by the interaction effect between the N type and the concentration. Compared to the control, the addition of N fertilizer promoted the growth of kenaf to varying degrees. Among all the treatments, the use of 2 mM of NO3−–N enhanced the biomass and Cd accumulation to the greatest extent compared to CK from 2.02 g to 4.35 g and 341.30 μg to 809.22 μg per plant, respectively. The NH4+–N significantly reduced the Cd contents of different parts but enhanced the translocation factors of Cd stem to root (TF S/R) and leaf to stem (TF L/S) by 34.29~78.57% and 45.10~72.55%, respectively. The peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) enzyme activities of the kenaf increased with the N treatments, especially with NH4+–N. Overall, applying low concentrations of NO3−–N can better promote the extraction of Cd by kenaf.

Metabolic Adjustment of Glycine max (L.) Merril in the Presence of Nitrate and Bradyrhizobium japonicum

Reactive oxygen species are generated during the processes of photosynthesis and nitrate reduction, which can compromise the integrity of biomolecules and membranes. During the vegetative phase of Fabaceae species, around half of translocated carbohydrate is used for nodule growth, while the other half returns to the aerial part with nitrogen incorporated. These sugars may be yet involved with membrane stabilization, signaling, and activation of important genetic pathways for plant development. Thus, the aim was to study the adjustments of the photosynthetic and antioxidant systems and the accumulation of carbohydrates and biomass in Glycine–Bradyrhizobium cultivated with nitrate (NO3−). Four treatments were evaluated in completely randomized blocks. Glycine–Bradyrhizobium was grown with 1.7 mM of NO3− (GB: 1.7 mM NO3−) and without NO3− (GB: 0 mM NO3−), and Glycine was grown with 1.7 mM of NO3− (G: 1.7 mM NO3−) and without NO3− (G: 0 mM NO3−). Glycine–Bradyrhizobium symbiosis contributes to photosynthetic metabolism and total sugars, reduces the action of antioxidant enzymes, and minimizes the use of nitrate in soybean cultivation.; Glycine–Bradyrhizobium with nitrate provided greater plant dry mass in the vegetative phase, along with increased enzymatic activity and reduced nodule mass.

Efficiency of arsenic remediation from growth medium through Bacillus licheniformis modulated by phosphate (PO4)3- and nitrate (NO3)- enrichment.

Bacillus licheniformis DAS-1 and DAS-2 were found as potent tool for removal/uptake of arsenic [As(V) and As(III)] and reduction [(As(V) to As(III)] of arsenic from the liquid growth medium in our previous studies. Present work gives light on modulation of arsenic remediation (in terms of uptake and reduction) by two selected essential soil nutrients, phosphate (PO4)3- and nitrate (NO3)-. PO43- has structural analogy with arsenate [AsO43-/As(V)] that compete with cell uptake of As(V). It was found that enrichment of 0.75mM of PO43- had significantly moderated the As(V) toxicity in liquid broth culture by retarding As(V) uptake. Lowering level of PO43- can lead to increase in As(V) removal from medium and vice versa. NO3- has strong oxidant properties which controls As(III) oxidation into As(V) in medium that resulted less toxicity favouring growth of bacteria and also more uptake via phosphate transporters. Hence, accelerated As(III) uptake has shown on enrichment of 0.5mM of NO3- in medium. All the results of work give evidence that appropriate enrichment of PO43- and NO3- into liquid growth medium, can significantly contribute in alteration of efficiency for arsenic removal/uptake and reduction by bacteria from the medium.

Effects of ultraviolet radiation on the morphophysiology of the macroalga Pyropia acanthophora var. brasiliensis (Rhodophyta, Bangiales) cultivated at high concentrations of nitrate

The abiotic and biotic factors of the environments are constantly changing, making sessile organisms, such as macroalgae, need to adjust to the given location. Two abiotic factors that change a lot are the nitrate (NO3−) concentration, thanks to the release of untreated sewage directly into the sea, and high irradiance due to the decrease in the ozone layer (O3). The goal of this study is to understand if the quantity of NO3− influences the growth rate, ultrastructure, concentration, and autofluorescence of photosynthetic pigments, and concentration secondary and antioxidant metabolites of the algae Pyropia acanthophora var. brasiliensis exposed to ultraviolet radiation (UVR). Experiments with the algae were carried out with exposure to 0, 25, 50, and 100 mM of NO3− and PAB (= PAR + UVAR + UVBR) for 3 h a day for a period of 7 days, all after an acclimatization of 7 days. In samples exposed to UVR, there was an increase in antioxidant metabolites, while the highest concentrations of total soluble sugars and starch were found in the samples exposed to PAB [0]. High growth rates were observed in samples cultured with NO3− without UVR. In samples exposed to UVR, a decrease in the growth rates occurred, but the NO3− contributed to maintain the positive growth rates. This samples showed no alterations in the structure of the thylakoids of chloroplasts and there was no decrease in their autofluorescence. The presence of different concentrations of NO3− in the culture favored the production of photosynthetic pigments and the production of phenolic compounds, contributing to minimize the effects of ultraviolet radiation.

Reduced Plasma Membrane H+-ATPase Isoform OsA7 Expression and Proton Pump Activity Decrease Growth Without Affecting Nitrogen Accumulation in Rice

Plasma membrane H+-ATPase (PM H+-ATPase, EC 3.6.1.3.) is a proton pump that is necessary to promote cell growth and ion fluxes across the plasma membrane. The main goal of this study was to evaluate the role of PM H+-ATPase isoform OsA7 expression in rice growth and nitrogen (N) accumulation using three genetically engineered lineages with artificial micro RNA (amiRNA) targeting OsA7 (osa7.1, osa7.2, and osa7.3). PM H+-ATPase isoform expression in rice shoots and roots (wild-type) revealed that OsA7 is highly expressed in roots and is the most highly expressed PM H+-ATPase isoform. The three osa7 lineages had lower fresh weight, grain yield, height, and 1000-grain weight compared to control IRS plants. The hydroponic experiment comprised three NO3− levels over 30 days: 0.2 mM NO3−–N, 2.0 mM NO3−–N, and NO3− starvation for 3 days. The three osa7 lineages had lower PM H+-ATPase and V-H+-PPase activity as compared to the IRS plants. The root and shoot fresh weights were lower in osa7 lineages. The root/shoot ratio was lower in the osa7 lineages cultivated without nitrogen for 3 days and with 0.2 mM of NO3−–N as compared to IRS, and did not change in plants cultivated with 2.0 mM NO3−–N. The total N concentration did not change in the three osa7 lineages as compared to IRS. Overall, the results indicate that OsA7 is important for rice growth, grain production, and root growth, but does not affect N accumulation, highlighting the importance of other PM H+-ATPase isoforms in N uptake.

Adaptation of euhalophyte Suaeda salsa to nitrogen starvation under salinity

Suaeda salsa L. (S. salsa) is an annual euhalophyte with high salt tolerance. The NO3− content in soils where S. salsa populations occur are very low, especially in intertidal habitat. However, it remains unclear how S. salsa populations adapt to low nitrogen environments. Plants of two S. salsa populations were pre-cultured with nitrate nitrogen (1 mM of NO3−-N) for 30 days. Then, the seedlings were cultured with 1 mM of NO3−-N and N-free solution (N starvation) at 200 mM of NaCl for an additional 14 days. The expression of two genes in S. salsa, nitrate transporter 1.7 (SsNRT1.7) and nitrate transporter 2.5 (SsNRT2.5) in old and mature leaves, was markedly upregulated during N starvation in the intertidal population, when compared to the inland population, but this was not the case in young leaves. After N starvation, the decrease in NO3− and chlorophyll content, net photosynthetic rate in young leaves, and shoot dry weight in the intertidal population were lower than those in the inland population. In conclusion, SsNRT1.7 and SsNRT2.5 may play a role in NO3− remobilization, especially in the intertidal population, during N starvation. This trait may benefit the intertidal population for adapting to low nitrogen environments.

Effects of high nitrate concentrations on the germination of carpospores of the red seaweed Pyropia acanthophora var. brasiliensis (Rhodophyta, Bangiales)

Pyropia is a genus of algae used in sushi. Nitrate (NO3−) is essential for its growth. Excess NO3− is flushed into seawater, as a result of anthropogenic activities, increasing the potential for higher than normal concentrations which could be harmful to both algae and humans. This study aims to evaluate the effect of NO3− on the morphology, ultrastructure, spore viability, autofluorescence of chloroplasts, and formation of cell wall, during germination of the red seaweed Pyropia acanthophora var. brasiliensis. To accomplish this, carpospores were cultivated at 24°C, 40 μmol photons m−2 s−1 with photoperiod of 12 h and exposed to 0, 25, 50, and 100 mM of NO3− for 2 days. Samples were cultured for another 5 days to measure the length of the germ tube. Concentrations of NO3− did not significantly influence the development, morphology, viability, or ultrastructure of the spores in the first 2 days. The absence of this nutrient did delay the ultrastructural development of the carpospore, decreasing autofluorescence of the chloroplast and delaying the formation of the cell wall and pyrenoid. Over the seven-day experimental period, higher concentrations of NO3− increased the size of the germ tube, indicating that this extra concentration boosted the development of P. acanthophora.

Identifying N sources that affect N uptake and assimilation in Vanda hybrid using 15N tracers

Vanda is an aerial tropical orchid native to Thailand and nitrogen (N) fertilizer is mainly used to promote its growth and quality. However, little is known about the characteristics of N absorption and assimilation in Vanda. The objective of this study was to determine the appropriate source of N for Vanda cultivation. In this experiment, shoots and roots of Vanda ‘Ratchaburi Fuchs-Katsura’ were sprayed weekly with 100 ml of 15N tracer solution (1) 10 mM of 15NO3−, (2) 5 mM of 15NO3− plus 5 mM of NH4+, (3) 5 mM of NO3− plus 5 mM of 15NH4+ and (4) 10 mM of 15NH4+. The results indicated that plants fed with a combined N fertilizer gave the highest of 15N use efficiency (15NUE) of about 21.8%, 30 days after the first feeding (DAF), compared with those fed sole sources of 15NO3− (21.0%) and 15NH4+ (16.6%). However, a sole nitrate fertilizer or combination fertilizer did not significantly affect the total N and labelled N content. Alanine was a major amino acid found in leaves and roots at 7 DAF, whereas glutamine was mainly found in stems. At 30 DAF, tyrosine and alanine became major components in the leaves, and glutamine decreased in stems when plants were fed with a single 15NH4+source.

Natural Fe-bearing manganese ore facilitating bioelectro-activation of peroxymonosulfate for bisphenol A oxidation

The natural Fe-bearing manganese ore (FMO) and bioelectricity supplied by a single-chamber microbial fuel cell (MFC) were employed to construct the peroxymonosulfate (PMS) activation system (FMO/MFC/PMS) for the degradation of bisphenol A (BPA). The FMO was characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results show that ε-MnO2 and α-Fe2O3 were the active components of the natural FMO and they could greatly facilitate the bioelectro-activation of PMS for the oxidation of BPA. When FMO dosage, PMS concentration and current density were set as 0.5 g L−1, 10 mM and 100 mA m−2, respectively, 97.8% of BPA degradation could be achieved at natural pH of BPA solution after 80 min reaction and about 80% of TOC could be removed when the reaction time was prolonged to 120 min. Based on the electron paramagnetic resonance result, scavenging tests, fluorescence spectra experiment and X-ray photoelectron spectroscopy analysis, both radical oxidation (sulfate and hydroxyl radical) and non-radical reactions (such as singlet oxygen and direct electron transfer) were considered to be responsible for BPA removal. The FMO exhibited good stability and could be recycled at least 3 runs without any additional special treatment. 10 mM of Cl− and HCO3− could suppress the degradation of BPA while 10 mM of NO3− showed negligible effects on BPA removal. The FMO/MFC/PMS process could be applied in natural water without the decrease of BPA removal.

Involvement of phosphoenolpyruvate carboxylase and antioxydants enzymes in nitrogen nutrition tolerance in Sorghum bicolor plants

Plants of Sorghum bicolor (C4 species) were grown at different nitrate or ammonium concentrations (0.5, 5, 20 and 50 mM) in order to examine the effect of nitrogen nutrition on growth, phosphoenolpyruvate carboxylase (PEPC) and antioxidant enzymes activities in both roots and leaves of 30-day-old plants. At high NO3− levels (20 and 50 mM) the fresh weight was significantly higher. When the nitrogen source was in ammonium form, the leaf and root mass increased drastically at low concentration 5 mM and significantly at 20 mM, however similar fresh weight was found at high level of ammonium (50 mM). The leaves catalase (CAT), guaiacol peroxidase (POD), glutathione reductase (GR), and glutathione S-transferase (GST) activities and the roots glutathione reductase and glutathione S-transferase activities were significantly higher in the NH4+-fed plants than those grown in the nitrate medium. Activity and proteins levels of phosphoenolpyruvate carboxylase in both leaves and roots of sorghum plants were increased progressively with increasing external nitrogen concentration. This increase was more pronounced at high level of ammonium (50 mM), being 2-fold at 50 mM of NO3− and 3-fold at 50 mM of NH4+. Our results suggested that antioxidant enzymes activities and PEPC play a key role in ammonium detoxification and tolerance in sorghum plants.

Growth, Quality Index, and Mineral Composition of Five Ornamental Cabbage Cultivars Grown Under Different Nitrogen Fertilization Rates

The fertilizer nitrogen (N) inputs to some potted plants such as ornamental cabbage (Brassica oleracea L. var. acephala D.C.) are frequently higher than the actual demand. Optimization of N fertilization rate and selecting N-efficient cultivars are important approaches to increase the nitrogen use efficiency (NUE) and to reduce environmental pollution from nitrate leaching. The aim of this study was to assess the effect of increasing levels of nitrate (0.5, 2.5, 5, 10, or 20 mm of NO3−) in the nutrient solution on plant growth, quality, soil plant analysis development (SPAD) index, chlorophyll fluorescence, leaf pigments, mineral composition, and NUE in five ornamental cabbage cultivars (Coral Prince, Coral Queen, Glamour Red, Northern Lights Red, and White Peacock), grown in closed subirrigation system. ‘Glamour Red’ and ‘Northern Lights Red’ needed 3.3 and 2.9 mm of NO3− in the supplied nutrient solution, respectively, to produce 50% of predicted maximum shoot dry weight (SDW), whereas the vigorous cultivars Coral Prince, Coral Queen, and White Peacock needed 5.5, 4.7, and 4.3 mm of NO3−, respectively. Total leaf area (LA), SDW, SPAD index, N, Ca, and Mg concentrations increased linearly and quadratically in response to an increase of the nitrate concentration in the nutrient solution. Irrespective of cultivars, fertilizing above 10 mm NO3− produced high-quality plants (quality index of 5) and resulted in sufficiently high tissue concentrations of N, P, K, Ca, Mg, and Fe.

Nitrate reduces the negative effect of UV radiation on photosynthesis and pigmentation in Gracilaria tenuistipitata (Rhodophyta): the photoprotection role of mycosporine-like amino acids

Barufi J.B., Mata M.T., Oliveira M.C. and Figueroa F.L. 2012. Nitrate reduces the negative effect of UV radiation on photosynthesis and pigmentation in Gracilaria tenuistipitata (Rhodophyta): the photoprotection role of mycosporine-like amino acids. Phycologia 51: 636–648. DOI: 10.2216/10.77.1Photoprotection of the agarophyte red alga Gracilaria tenuistipitata against ultraviolet radiation (UVR) was investigated in algae submitted for 1 week to photosynthetically active radiation (PAR, 260 μmol photons m−2 s−1) or PAR + UVR (UV-A, 8.13 W m−2 and UV-B, 0.42 W m−2) under different nitrogen concentrations: 0, 0.1, and 0.5 mM of NO3−. Photosynthetic pigments decreased during the time of the experiment mainly under low nitrogen supply and UVR. Incubation under high nitrogen supply (0.5 mM) sustained the photosynthetic levels over time. In contrast, mycosporine-like amino acids (MAAs) increased up to eightfold in the presence of UVR and 0.5 mM NO3−. Under PAR + UVR, maximal quantum yield was positively correlated to MAA abundance, whereas under PAR no correlation was found. The photosynthetic yield of algae cultivated during seven days under PAR + UVR was less affected by a 30-min exposure of high UVR (16 W m−2) and fully recovered after transferring to low PAR irradiances, whereas algae kept under PAR were more affected by UV exposure and no full recovery was observed. Growth rates decreased after three days in the presence of UVR and under low nitrate supply. However, these rates were similar when compared with treatments of PAR and PAR + UVR after seven days, with the exception of samples in 0 mM NO3−, indicating that the acclimation after one week's exposure is related to nitrate supply. In conclusion, the lowest negative effect of UVR on photosynthesis and growth rate in high N-supply-grown algae could be explained by the stimulation of photoprotection mechanisms, such as accumulation of MAAs. Photostimulation of MAA accumulation by UVR under high N supply was observed in G. tenuistipitata even after 20 years in culture without the induction of this photomorphogenic light signal.

OsDof25 expression alters carbon and nitrogen metabolism in Arabidopsis under high N-supply

To verify the effect of the transcription factor OsDof25 on the nitrogen metabolism in plants, it was cloned for expression in Arabidopsis thaliana under the control of the 35S promoter. Lineages with different expression levels of this gene were obtained, and when grown in a half-strength MS medium (10 mM of NH4 + and 20 mM of NO3 −) showed phenotypes with visible chloroses and growth disorders. It was observed that OsDof25 increased the levels of expression of high and low affinity ammonium transporters (AtAMT1.1 and AtAMT2.1, respectively) and repressed the high affinity nitrate transporter (AtNRT2.1). We also verified an increase in total amino-N content and expressions of the pyruvate kinase (PK1 and PK2), phosphoenolpyruvate carboxylase (PEPC1 and PEPC2) and NADP-dependent and NAD-dependent isocitrate dehydrogenase. In addition, an increase in expression levels and activity of glutamate dehydrogenase was also observed. The simultaneous increase in the expression of AMTs and enzymes of carbon metabolism may explain the high levels of amino-N found in the transgenic plants. The data found in this work suggest that OsDof25 expression simultaneously affects NH4 + uptake and organic acid metabolism in plants.

Nitrogen‐use efficiency traits of mini‐watermelon in response to grafting and nitrogen‐fertilization doses

AbstractTwo experiments were conducted to study the effect of grafting on nitrogen‐use efficiency (NUE) in mini‐watermelon plants. In the first study, mini‐watermelon plants (Citrullus lanatus [Thumb.] Matsum. and Nakai cv. Minirossa) either ungrafted or grafted onto Macis, Vita (Lagenaria siceraria [Mol.] Standl.), PS1313, and RP15 (Cucurbita maxima Duchesne × Cucurbita moschata Duchesne) rootstocks grown in hydroponics were compared in terms of shoot dry biomass, leaf area, root‐to‐shoot ratio, SPAD index, shoot N uptake, and nitrate reductase (NR) activity 40 d after transplantation in response to nitrate concentration in the nutrient solution (0.5, 2.5, 5, 10, 15, or 20 mM of NO$ _3^- $). In the second experiment, the suitability of a selected rootstock with high NUE (Vita) to improve crop performance and NUE of grafted mini‐watermelon plants was evaluated under field conditions. In the hydroponic experiment mini‐watermelon grafted onto Vita rootstock needed the lowest nitrate concentration (1.31 mM of NO3) in the nutrient solution to reach half maximum shoot dry weight. Total leaf area, SPAD index, and shoot N uptake increased in response to an increase of N concentration in the nutrient solution. At 2.5 mM NO$ _3^- $, mini‐watermelon grafted on either Vita or RP15 had the highest NR activity whereas no significant difference was observed at 10 mM NO$ _3^- $. The open‐field study indicated that increasing N‐fertilization rates from 0 to 100 kg ha–1 improved total and marketable yields of mini‐watermelon plants while decreasing NUE. When averaged over N levels, the marketable yield, NUE, N‐uptake efficiency, and N‐utilization efficiency were significantly higher by 39%, 38%, 21%, and 17%, respectively, in Minirossa grafted onto Vita compared to ungrafted Minirossa plants. Therefore, grafting mini‐watermelon plants onto selected rootstocks can be used as a quick and effective method for improving productivity and NUE.

Improving Nitrogen Use Efficiency in Melon by Grafting

Identification of rootstocks capable of improving the nitrogen use efficiency (NUE) of the scion could reduce N fertilization and nitrate leaching; however, screening different graft combinations under field conditions can be costly and time-consuming. This study evaluated a rapid and economical methodology for screening of melon rootstocks for NUE. Two experiments were designed. In the first, melon plants (Cucumis melo L. cv. Proteo) either ungrafted or grafted onto four commercial rootstocks: ‘Dinero’ and ‘Jador’ (Cucumis melo L.), ‘P360’, and ‘PS1313’ (Cucurbita maxima Duchesne × Cucurbita moschata Duchesne) grown in hydroponics were compared in terms of shoot dry biomass, leaf area, root-to-shoot ratio, SPAD index, shoot N uptake, and nitrate reductase (NR) activity at the early developmental stage in response to nitrate availability (0.5, 2.5, 5, 10, or 15 mm of NO3–). The second experiment was aimed to confirm whether the use of a selected rootstock with high NUE (‘P360’) could improve crop performance and NUE of grafted melon plants under field conditions. In the first experiment, carried out under greenhouse conditions, melon plants grafted onto ‘Dinero’, ‘Jador’, and ‘P360’ rootstocks needed 5.7, 5.2, and 6.1 mm of NO3–, respectively, to reach half-maximum shoot dry weight, whereas plants grafted onto ‘PS1313’ rootstock and the control treatment (ungrafted plants) needed 9.1 and 13.1 mm of NO3–, respectively. Total leaf area, SPAD index, and shoot N uptake increased linearly and quadratically in response to an increase of the N concentration in the nutrient solution. At 2.5 mm of NO3–, melon plants grafted onto both C. melo and Cucurbita maxima × Cucurbita moschata rootstocks had the highest NR activity, whereas no significant difference was observed at 10 mm of NO3–. In the second experiment, carried out under open field conditions, increasing the N fertilization rates from 0 to 120 kg·ha−1 increased the total and marketable yields of melon plants, whereas the NUE decreased. When averaged over N levels, the marketable yield, NUE, and N uptake efficiency were higher by 9%, 11.8%, and 16.3%, respectively, in ‘Proteo’ grafted onto ‘P360’ than in ungrafted ‘Proteo’ plants.

Effects of electron donors and acceptors on anaerobic reduction of azo dyes by Shewanella decolorationis S12

Shewanella decolorationis S12 was able to reduce various azo dyes in a defined medium with formate, lactate, and pyruvate or H(2) as electron donors under anaerobic conditions. Purified membranous, periplasmic, and cytoplasmic fractions from strain S12 analyzed, respectively, only membranous fraction was capable of reducing azo dye in the presence of electron donor, indicating that the enzyme system for anaerobic azoreduction was located on cellular membrane. Respiratory inhibitor Cu(2+), dicumarol, stigmatellin, and metyrapone inhibited anaerobic azoreduction by purified membrane fraction, suggesting that the bacterial anaerobic azoreduction by strain S12 was a biochemical process that oxidizes the electron donors and transfers the electrons to the acceptors through a multicompound system related to electron transport chain. Dehydrogenases, cytochromes, and menaquinones were essential electron transport components for the azoreduction. The electron transport process for azoreduction was almost fully inhibited by O(2), 6 mM of NO3-, and 0.9 mM of NO2-, but not by 10 mM of Fe(3+). The inhibition may be a result from the competition for electrons from electron donors. These findings impact on the understanding of the mechanism of bacterial anaerobic azoreduction and have implication for improving treatment methods of wastewater contaminated by azo dyes.

Estimating the Nitrogen Concentration of Strawberry Plants from Its Spectral Response

Estimating the nitrogen (N) status of plants as a function of their spectral response is a promising technique to diagnose and optimize N fertilization. An experiment was conducted in Jiquilpan (Michoacán, México) in which three N levels (0.3, 3, and 20 mM of NO3 − in the irrigation water) were applied to strawberry (Fragaria vesca) in a randomized complete block design with three replicates. The spectral response of strawberry was measured at both the canopy and leaf level using individual wavebands as well as vegetation indices. Individual leaves were separated into three strata (young, mature, and old) and leaf dry matter, leaf area, and N content (% dry matter) were measured in each stratum. Leaf area, biomass, and N content differed significantly between strata. Leaf area, biomass, and N content in all strata were affected by N fertilization. At the canopy level, N content was highly correlated with green reflectance (R550) (r2=0.50) and red reflectance (R680) (r2=0.60) as well as the vegetation indices simple ratio (SR) (r2=0.56), normalized difference vegetation index (NDVI) (r2=0.56), and hyperspectral NDVI (HNDVI) (r2=0.56). For individual leaves, significant differences between strata were found with normalized total pigment to chlorophyll a ratio index (NPCI) and MERIS terrestrial chlorophyll index (MTCI) (p<0.001) as well as R550, photochemical reflectance index (PRI), red edge position (REP), and REP calculated using the MERIS satelite wavelengths (p<0.01). Relationships between spectral indices and N content at the leaf level were found with the youngest leaves only, with NPCI (p<0.01) and MTCI (p<0.05), whereas only R550 responded to N fertilization (p<0.05).