A simple and rapid micro-Kjeldahl method for total nitrogen analysis

The presence of enteric bacteria in water bodies is a cause of public health concerns, either by directly causing water- and food-borne diseases, or acting as reservoirs for antibiotic resistance determinants. Water is used for crop irrigation; and sediments and aquatic plants are used as fertilizing supplements and soil conditioners. In this work, the bacterial load of several micro-environments of the urban lake of Xochimilco, in Mexico City, was characterized. We found a differential distribution of enteric bacteria between the water column, sediment, and the rhizoplane of aquatic plants, with human fecal bacteria concentrating in the sediment, pointing to the need to assess such bacterial load for each micro-environment, for regulatory agricultural purposes, instead of only the one of the water, as is currently done. Resistance to tetracycline, ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole was common among Escherichia coli isolates, but was also differentially distributed, being again higher in sediment isolates. A distinct distribution of chloramphenicol minimum inhibitory concentrations (MIC) among these isolates suggests the presence of a local selective pressure favoring lower MICs than those of isolates from treated water. Fecal bacteria of human origin, living in water bodies along with their antibiotic resistance genes, could be much more common than typically considered, and pose a higher health risk, if assessments are only made on the water column of such bodies.

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“…Total organic carbon (TOC) was determined using an Apollo 9000, Tekmar-Dohrmann analyzer, and total nitrogen by micro-Kjeldahl method [22].…”

Section: Physical-chemical Analysesmentioning

confidence: 99%

Characterization of Escherichia coli Isolates from an Urban Lake Receiving Water from a Wastewater Treatment Plant in Mexico City: Fecal Pollution and Antibiotic Resistance

et al. 2015

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“…The plant N status was measured by determining LNC (%) and plant biomass. At all the phenostages, the plant samples were collected and total N concentration in leaves was determined by the Micro-Kjeldahl method (Guebel et al 1991). Plant dry biomass was measured after the plant sample dried to a constant weight after incubation at 60-70 • C. PNA (g N m −2 ) was calculated as the product of LNC and total dry biomass per unit ground area.…”

Section: Measurementsmentioning

confidence: 99%

Assessment of plant nitrogen stress in wheat (Triticum aestivum L.) through hyperspectral indices

Ranjan

Chopra

Sahoo

et al. 2012

International Journal of Remote Sensing

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A field experiment with wheat was conducted with four different nitrogen and four different water stress levels, and hyperspectral reflectances in the 350-2500 nm range were recorded at six crop phenostages for two years (2009-2010 and 2010-2011). Thirty-two hyperspectral indices were determined using the first-year reflectance data. Plant nitrogen (N) status, characterized by leaf nitrogen content (LNC) and plant nitrogen accumulation (PNA), showed the highest R 2 with the spectral indices at the booting stage. The best five predictive equations for LNC were based on the green normalized difference vegetation index (GNDVI), normalized difference chlorophyll index (NDCI), normalized difference 705 (ND 705 ) index, ratio index-1dB (RI-1dB) and Vogelman index a (VOGa). Their validation using the second-year data showed high R 2 (>0.80) and ratio of performance to deviation (RPD; >2.25) and low root mean square error (RMSE; <0.24) and relative error (<10%). For PNA, five predictive equations with simple ratio pigment index (SRPI), photochemical reflectance index (PRI), modified simple ratio 705 (mSR 705 ), modified normalized difference 705 (mND 705 ) and normalized pigment chlorophyll index (NPCI) as predicting indices yielded the best relations with high R 2 > 0.80. The corresponding RMSE and RE of these ranged from 1.39 to 1.13 and from 24.5% to 33.3%, respectively. Although the predicted values show good agreement with the observed values, the prediction of LNC is more accurate than PNA, as indicated by higher RMSE and very high RE for the latter. Hence, the plant nitrogen stress of wheat can be accurately assessed through the prediction of LNC based on the five identified reflectance indices at the booting stage.

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“…Shoots were oven dried at 70°C for 48 h, weighted in a precision balance and powdered with a mill ball IKA Labortechnik A10 (Janke & Kunkel GmbH & CO). Total nitrogen from shoot dry biomass was quantified by Kjeldahl technique (Guebel et al 1991), carried out in the Laboratório Químico Agrícola Rebelo da Silva (Lisbon, Portugal). A sample of 2 mg shoot dry biomass was weighted into tin capsules and sent for isotope ratio mass spectrometry analysis (IRMS) (Brenna et al 1997) at the University of the Balearic Islands, Balearic Islands, Spain.…”

Section: Methodsmentioning

confidence: 99%

Broad environmental tolerance of native root-nodule bacteria ofBiserrula pelecinusindicate potential for soil fertility restoration

Vicente

Pérez‐Fernández

2016

Plant Ecology & Diversity

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Background: Biserrula pelecinus is an annual legume native to the Mediterranean basin, found in pastureland, alone or in association with other legumes (Leguminosae) and grasses (Poaceae). It has been used in revegetation programmes of mining wastes showing phytoremediation potentials and thus becoming potentially highly attractive for plant ecology and restoration management of natural ecosystems. Aims: To characterise native root-nodule bacteria isolated from B. pelecinus from the Iberian Peninsula, and to select suitable N fixers for field-application and soil rehabilitation. Methods: Strains were isolated and molecularly identified by 16S rRNA amplification and sequencing. Strains were phenotypically characterised in different abiotic conditions (acidity, salinity and heavy metals) and tested for their ability to fix atmospheric N 2 . The most suitable N fixers were applied in greenhouse experiments with B. pelecinus under different fertilization levels to assess their tolerance to fertilized and polluted soils, commonly encountered in restoration projects. Results: B. pelecinus root-nodule isolates tolerated pH from 4.5 to 9.5 grew in saline conditions (2.5% of NaCl), and tolerated 50 µM of Al 3+ and Mn 2+ . Three isolates efficient in N 2 fixation, relative to the reference Mesorhizobium strain, were considered excellent candidates for the amelioration of nutrient poor sites. Conclusions: These results provide valuable information for the potential use in soil restoration of B. pelecinus in a widerange of conditions, exploiting the natural variability of its root-nodule bacteria.

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A simple and rapid micro-Kjeldahl method for total nitrogen analysis

Cited by 69 publications

References 8 publications

Characterization of Escherichia coli Isolates from an Urban Lake Receiving Water from a Wastewater Treatment Plant in Mexico City: Fecal Pollution and Antibiotic Resistance

Characterization of Escherichia coli Isolates from an Urban Lake Receiving Water from a Wastewater Treatment Plant in Mexico City: Fecal Pollution and Antibiotic Resistance

Assessment of plant nitrogen stress in wheat (Triticum aestivum L.) through hyperspectral indices

Broad environmental tolerance of native root-nodule bacteria ofBiserrula pelecinusindicate potential for soil fertility restoration

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