Nitrogen Cycle - Science topic

Good feedback by Mohebul Ahsan. However, it should keep in mind that this equation gives the overpotential for any electrochemical reaction.

Also check please the following very good link: https://ageconsearch.umn.edu/record/118041/files/11.pdf

Kindly consult this article:

CARBON FOOTPRINT OF SELECTED CEREAL AND LEGUME CROPS CULTIVATED IN THE OLD BRAHMAPUTRA FLOODPLAIN SOIL

my original reply applies

Yes it's true because organic matter contents increase microbial population so that's why it takes part in mineral uptaken by plants

Nice question

In general, the gene number copies is expressed in relation to the suspension volume or sample mass (i.e. number of 16S gene copies per mL or number of 16S gene copies per gram of soil). The number of gene copies can also be expressed in Log10. While functional genes are expressed in relation to the total abundance of the community (16S rRNA). For example, number of nifH gene copies / number of 16S rRNA gene copies.

Dear T.J. Samojedny ,

Indeed, a good point. I see papers like:

Cole, J. C., Smith, M. W., Penn, C. J., Cheary, B. S., & Conaghan, K. J. (2016). Nitrogen, phosphorus, calcium, and magnesium applied individually or as a slow release or controlled release fertilizer increase growth and yield and affect macronutrient and micronutrient concentration and content of field-grown tomato plants. Scientia Horticulturae, 211, 420-430.

https://www.sciencedirect.com/science/article/pii/S0304423816304691

were the ‘formal’ notation is ‘loosely’ used. I think everybody understands that when talking about Mg content in these type of studies is actually Mg2+.

Personally, I would use Mg2+ as much as possible or talk about Mg ions, but I can imagine that in other disciplines other notations are tolerated or simply more costume.

Best regards.

In the alternative, you may use Deep-Water-Culture technique of aquaponics to grow some useful vegetables which biologically utilize ammonia-nitrogen in form of nutrients. You may quantify the nutrients by running the proximate analysis of the vegetables after harvest. Read further. Thanks. @

Calculation details here

Plants those love to take nitrogen in aerobic condition they uptake nitrogen as ammonium, generally maximum vegetables uptake their nitrogen as nitrate form. Plants those growing in submersible /anaerobic condition as rice love to take up nitrogen as nitrate.

Good idea .

NO2 and other NOx interact with water, oxygen and other chemicals in the atmosphere to form acid rain. Acid rain harms sensitive ecosystems such as lakes and forests.

Please check the following PDF attachments.

Bubbling may occur due to aquatic plants or algae.

In my opinion, from your table and figure, your two results are consistent instead of contradictory.

In addition to the pipeline mentioned above ( ), you can also have a look at this one:

Thanks Shan Thomas i will check it out, looks like a more convenient solution than trolling through papers

The form of N and the fate of N in the soil-plant system is probably the major driver of changes in soil pH in agricultural systems.

Nitrogen can be added to soils in many forms, but the predominant forms of fertilizer N used are urea (CO(NH2)2), monoammonium phosphate (NH4H2PO4), diammonium phosphate ((NH4)2HPO4), ammonium nitrate (NH4NO3), calcium ammonium nitrate (CaCO3+NH4(NO3)) ammonium sulfate ((NH4)2SO4), urea ammonium nitrate (a mixture of urea and ammonium nitrate) and ammonium polyphosphate ([NH4PO3]n).

The key molecules of N in terms of changes in soil pH are the uncharged urea molecule ([CO(NH2)2]0), the cation ammonium (NH4+) and the anion nitrate (NO3-).

The conversion of N from one form to the other involves the generation or consumption of acidity, , and the uptake of urea, ammonium or nitrate by plants will also affect acidity of soil.

Good for you. Ramiro, however, to whom your " You need to use both IPTG and X-Gal" advice was addressed, does.

Yes, i agree with Dr. Rosa that Enzymes involved are key to understand this process in natural marine environments. So, better check literature on nitrogen species conversion processes.

Best!

Please have a look at these PDFs..

Thank you very much Gustavo,

Really appreciate your comments.

There are many soil-based tests of N availability.  It's a case of finding one (or more!)  that makes sense in the context of what you wish to examine.  Soil extracts can used to localise different pools of N, e.g. by extracting with water (N in free solution), salt solution (free solution + adsorbed), CHCl3 + salt solution (free solution + adsorbed + microbial).  For each type of extract one could measure total pools of inorganic N or organic N, or even measure specific compounds or classes of organic N (e.g. amino acids).  There is also the option of measuring the rate at which inorganic forms of N are produced, i.e. various mineralisation assays.  There are suggestions that depolymerisation may be the limiting step in supplying plant-available forms of N, and thus it could be useful to measure rates of proteolysis as an indicator of N availability (see attached paper)

A nutrient budget takes into account all the nutrient inputs on a farm and all those removed from the land.

Abstract : The nutrient (P and N species) and chloride budgets were investigated in a representative floodplain in the seasonal wetlands of the Okavango Delta, Botswana. A variety of sources of nutrients in the surface water were considered, namely ion species coming with the floodwater, those generated from dry floodplain soils and those from water-soluble dust deposition (both local and long-range sources). Concentrations of total-nitrogen and chloride in surface water were below 1 mg l1 . Total-phosphorus concentrations were 0.05 mg l1 , reflecting the oligotrophic character of the system. Dust deposition rates were highest for chloride at 2.44 g m2 year1 followed by 0.79 g m2 year1 for total-N, 0.40 g m2 year1 for ammonia and only 0.02 g m2 year1 for total-P, respectively. Chloride was derived primarily from long-range transport, while N and P species were of more local origin. Dissolution rates for these ions combined were calculated to be 3.9 g m2 for the flooded area in the 1999 season and thus all dry deposits must be re-dissolved. The accumulation of dust deposits on dry surfaces and their subsequent dissolution causes 2–5 times higher concentrations of nitrogen, phosphorus and chloride with the onset of the flood, thus boosting the nutrient stock in the crucial phase of the onset of flooding. Chloride dissolved from dry soil surfaces and dust contributed approximately 40% to the overall floodplain budget. Although contributions from the soil surface and dust to the nitrogen and phosphorus pools of the floodplain are less prominent (with 10% of total), they nonetheless represent a significant source of nutrients in the entire system. Extrapolation to annually flooded swamps (10,000 km2 ) indicates a maximum contribution of 40% for total-nitrogen and 60% for total-phosphorus from dust deposition on wet or dry surfaces to the nutrient pool of the water body.Source :Wetlands Ecology and Management (2006) 14:253–267 Springer 2006,DOI: 10.1007/s11273-005-1115-0

Dear Yinan , please find an interesting work entitled Adjustment of microbial nitrogen use efficiency to carbon:nitrogen imbalances regulates soil nitrogen cycling  published in Nature Communications 5, Article number: 3694 (2014)

doi:10.1038/ncomms4694

Abstract

Microbial nitrogen use efficiency (NUE) describes the partitioning of organic N taken up between growth and the release of inorganic N to the environment (that is, N mineralization), and is thus central to our understanding of N cycling. Here we report empirical evidence that microbial decomposer communities in soil and plant litter regulate their NUE. We find that microbes retain most immobilized organic N (high NUE), when they are N limited, resulting in low N mineralization. However, when the metabolic control of microbial decomposers switches from N to C limitation, they release an increasing fraction of organic N as ammonium (low NUE). We conclude that the regulation of NUE is an essential strategy of microbial communities to cope with resource imbalances, independent of the regulation of microbial carbon use efficiency, with significant effects on terrestrial N cycling. PDF enclosed for further reading...

CO₂ retention or release from water or wastewater is pH dependant with pH<7 promoting CO₂ release, hence nitrification can be expected to reduce inorganic-C via two pathways, (a) nitrifiers use CO₂ as a C source to fix C and (b) CO₂ release by acidity_. However, inorganic-C dynamics may not be entirely influenced by nitrification. Aeration to promote nitrification can also promote CO₂ release by oxidation of organic-C. If we ignore the above, continuous nitrification without denitrification could rate limit nitrification since nitrification rates are lower below pH<7 with high build-up of H⁺, thereby self-limiting the release of CO₂ by high acidity. It could be argued that triggering denitrification by ceasing aeration at this point in a 'combined system' could promote alkalinity and when aeration commences again, there is greater potential for nitrification and release and use of CO₂.

thank you Bruce, I'm not crazy

MSN-Br you mean ATRP initiator grafted Silica? If yes, see in that case you have sufficient initiator grafted on silica surface which can assist to graft (/hold) considerable number of chains on particles. I think in your case instead of surface initiated polymerization the cross-linking (both acrylate and ring opening of epoxide) may be giving you the insoluble polymer. OR it is also possible that during detachment HF mediated ring opening is leading to cross-linking which leads to insoluble polymer (less sure about this one but look for some ref.)

In the second case where you have PEGMA functionalized Si you can simply carry out free radical polymerization than ATRP it can also guarantee good polymer grafting.

Dr. Souza, FTIR identifies and qualifies sensitivity to mineral and organic bonds that compose soil minerals and organic matter. To know the limitations and potential you may go through the attached file.

Thank u so much Hector for your helpful and detailed answer.

Dear Nasir,

COD/NO3 ratio in denitrification is a smart way  to ensure your bacteria gets a right dose of electron donor (i.e COD) for reducing your nitrates (electron acceptor).  You must calculate this ratio from your initial concentrations i.e how much COD is available for reduction of say X mg of nitrates.

No, this is not possible. Neither by HPLC-IRMS because this technique is used for d13C analysis for now due to a lack of optimization of the instrumentation. None of the commercial enterprises dealing with IRMS is ready for that even if it is reallly interesting.

Portia,

The objective of this test is to determine NH₄-N production after a 7-day anaerobic incubation.  As incubation is done under anaerobic conditions, all NH₄+ produced during the incubation remains as NH₄+ since the nitrification is restricted by anaerobic conditions.  It is true that any already existing NO₃- in the soil sample can be denitrified; but, it does not matter, since the aim of the test is to measure potentially mineralizable N.  It is the biological N availability index recommended by Keeney (1982) and the purpose and usefulness of the test is well explained in Keeney, D.R., 1982. (N availability indices.  Page 711-733, Methods of Soil Analysis Part 2.Agron. Monogr. 9 ASA & SSSA).

Hi Paul,

  Thank you very much for your reply. Amanita thiersii is mostly invading in the Midwest but I imagine that lawn care practices have mostly shifted similarly with time across the country. To give you more background, below I give the title and draft abstract of the study. Superscripts and subscripts were lost when I pasted.

Cheers,

Erik

The invasive fungus Amanita thiersii integrates site nitrogen and carbon dynamics across C3 and C4 lawns

Amanita thiersii is an invasive, saprotrophic fungus that is expanding its range rapidly in Midwestern lawns. Carbon isotope (δ13C) values from sporocarps collected between 1982 and 2009 correlated positively with mean annual temperature (MAT) and negatively with mean annual precipitation (MAP), reflecting presumably the relative use of C3 and C4 grasses in lawns. In addition, δ13C values correlated positively with the Suess effect, the drop in δ13C and increase in CO2 concentrations caused by anthropogenic fossil fuel combustion, with a coefficient of 4.9 rather than the expected value of 1. The apparent 13C discrimination accordingly increased by ~2.3‰ (check?) as CO2 concentrations rose by ~40 ppm over this time period. This enhanced 13C discrimination probably reflects increased assimilation by A. thiersii of C3-derived carbon, either resulting from management changes (increases in the planted proportion of C3 lawn grasses over time) or increased quantum yield and productivity of C3 grasses relative to C4 grasses with rising CO2 concentrations. Sporocarp nitrogen isotope (δ15N) values correlated positively with MAT and negatively with MAP, with a negative interaction of MAT with year. The negative correlation with MAP was three times stronger than in natural grasslands, suggesting that fertilization and watering of lawns in drier environments has enhanced 15N-depleted losses much more than in wetter environments. Isotopes in Amanita thiersii may integrate shifts over the last 50 years in lawn maintenance practices, soil nitrogen dynamics, and the physiological responses of turf grasses.

One point which has not been covered is various  path ways  of N losses especially through denitrification (N2O and N2 gases),volatilization( losses of ammoniacal  N ) and leaching losses of nitrate N.From climate change point of view the  gaseous forms of N  emissions  especially through denitrification are important.

What is mentioned above is true, chamber based method provides a snapshot of gas emissions at the time of chamber deployment, while micro-met methods provide non-intrusive, area integrated continuous measurements.  Both methods have their advantages and disadvantages. 

As Brian already explained, chamber method is considerably less expensive, allows for the inclusion of many sampling sites in a small plot-scale field experiment, and can be adapted to wide range of research objectives, while micro-meteorological techniques require expensive instrumentation and demands more skillful operation.  For many who wish to measure soil surface greenhouse gas fluxes, micro-meteorological techniques are beyond the reach of their resource availability (especially in the developing countries).

However, that doesn’t mean that this area of research is out of reach.  If standard protocols related to chamber deployment and gas sampling frequency are followed properly, one can generate high quality data of soil surface gas fluxes (that are not second in quality to data obtained using micro-meteorological techniques).

Here is a link that provides a detailed protocol developed by USDA-ARS GRACEnet Project.  It explains standard guidelines for chamber construction, deployment, gas sampling and analysis and data interpretation.  If followed properly one can obtain a good data set.

Hope this will be useful.

Hi

You can find some interestin information on this  link:

Hello Ramendra,

We have grown wild rocket (arugula) in our home garden and under home garden conditions it does not require any fertilizer.  All it needs is good quality compost and continuously moist soil conditions.

After seeing your question, I did a Google search and found the following paper that may be useful.  I am adding the abstract of the paper and the internet link for the full paper.  Hope that you would be able to get the full paper, otherwise, please let me know.  I can forward a copy.

Factors influencing tissue nitrate concentration in field-grown wild rocket (Diplotaxis tenuifolia) in southern England ( available at: http://www.tandfonline.com/doi/abs/10.1080/19440049.2012.696215?journalCode=tfac20)

Abstract

Wild rocket (Diplotaxis tenuifolia) is a leafy vegetable known for its high tissue nitrate concentration (TNC) which can exceed the limits set in the relevant European legislation designed to protect human health. The aim of this work was to understand the factors influencing TNC and to develop best practice guidelines to growers. Commercial crops of field-grown wild rocket were studied over two seasons. In 2010, ten separate crops were sampled representing a range of soil types and time periods during the summer. Two fields sampled using a ‘W’- or ‘X’-shaped sampling pattern demonstrated that 10 incremental samples bulked to make 1 kg of fresh material could be used to provide an adequate sample for determination of TNC in the wild rocket crop, as is the case for other leafy vegetables. Of eight commercial crops sampled in 2010 with an average nitrogen (N) fertiliser application of 104 kg N ha−1, two exceeded the limit of 6000 mg  kg−1 set in the legislation. In 2011, six N response experiments were carried out, and only two sites showed a significant yield response to N fertiliser. The reason for the lack of response at the other sites was principally due to high levels of soil mineral N prior to drilling, meaning the crops’ requirement for N was satisfied without additional fertiliser N. In the experimental situation at an N fertiliser application rate of 120 kg N ha−1, 50% of crops would have exceeded the 6000 mg  kg−1 limit. In both seasons, low radiation levels in the 5 days prior to harvest were shown to increase TNC, although the relationship was also influenced by N supply. Strategies for optimising N nutrition of field-grown wild rocket are discussed.

Annamox bacteria are autotrophic and oxidize ammonia anaerobically using nitrite as the electron acceptor.  They cannot tolerate oxygen and therefore can be found in reactors/conditions which  are anaerobic. For this you need to use NH3 and nitrite (from partial nitrification) at a ratio of ~1: 1.1 in the reactor feed in order to be able to conduct the above biochemical reaction. Further the carbon load (CBOD) should be very low for their enrichment. If you have high CBOD, annamox bac will not grow or activate in the reactor. Annamox bacteria are extremely slow growers and their doubling time is ~ 11 days. Therefore you need to maintain adequate SRT in your reactor in order to enrich these bacteria.  Enrichment can be done using conventional sludge may be granules/flocs from an anaerobic reactor.  

In my opinion, the paper "Quantification of anaerobic ammonium-oxidizing bacteria

in enrichment cultures by real-time PCR" in Water Research can give important information about the real-time PCR primers for Anammox bacteria. 

 I agree with the others, first it must be very clear the gas specie: molecular nitrogen? or a isotopomer of it? or other nitrogen compounds like N2O, or NOx? or do you want some of the nitrogen compounds? which ones? and where you want to collect the nitrogen in air? or is soil? if in air, you need a evacuated gas cylinder, use a GC-TCD with columns that separates permanent gases and  a GC gas inlet that take a few mbar (below the atmospheric pressure). Contrary to NOx, N2 and N2O are very stable with low humidity and oxygen in the sampling cylinder. In the National Metrology Institutes the N2 in measurement standards is normally a balance gas, so we do not measure it for calibration standards, like Certified Reference Materials (CRM), normally we measure in the N2 only the critical impurities for the application of the CRM. But you can measure N2 by GC-TCD!

It is true that both of these processes involve conversion to ammonia/ ammonium but the starting nitrogen form is different. Ammonification is the mineralization of organic nitrogen into ammonia. Dissimilatory nitrate/nitrite reduction to ammonia (aka DNRA) starts with inorganic nitrogen (nitrate/nitrite), not organic N. The nitrate/ nitrite is then reduced to ammonia/ ammonium. 

Dear Andrzej,

I am very familiar with organic matter and nutrient cycling in shallow marine sediments, but not so much with freshwater sediments. However, I did a brief search on the topic and I recommend you look at the following, that may also provide leads to other studies.

If you need information on marine systems, please let me know.

Best regards,

Angelos.

Oxidation state of N in nitrite is +3 and N in ammonia is -3. Therefore, net change of electrons in annamox reaction is 0.

In the first step of nitrification (oxidation of ammonia to nitrite) there is no need in additional electrons. BUT there is "hidden" requirement of electrons to "prepare" oxygen for hydroxylation of ammonia. Ammonium monooxygenase does not use O from water for hydroxylamine formation it does use O from O2. For this it needs to bring O with zero oxidation state to O with -2 oxidation state. Here additional electrons are required. However, in general equation this is "hidden" by the usage O2 as electron acceptor.

What both processes require is so called reverse electron transfer: to bring electrons released at higher redox potential reaction into lower redox potential reaction. In both cases that are reactions of assimilation of CO2. That normally is achieved by ATP hydrolysis (or any other reactions) that brings up the proton motive force and makes energetically unfavorable reaction to occur.

Dear Jean-Michel, 

Thank you to your opinion/suggestion. We will try to split the dataset and to use separate trophic enrichment factor for primary and secondary consumers, but how to deal with intermediate consumers?

And of course, I agree with you that a deep knowledge of the trophic web is necessary before to use mixing models.

Merci.

The B value basically refers to the fractionation that occurs for the two N isotopes. As a plant takes up nitrogen it preferentially uptakes the lighter isotope, 14N, by a small degree. This is something that would have to be determined experimentally, but there are also a range of generic values that you could use. I will paste a section below that discusses some of that. It is obviously important to know the δ15N of your soil...the larger the difference between the soil and the air then the less significant the B value is. You could do the experiment with the entire range of B values, and then say your results fall within that range of nitrogen fixation to be safe. Or to do your calculations with one "best guess" B value, and note that the B value may change. I will paste a couple sections below that may help.

Isotope fractionation constants are ex-

pressed as β in the expression 14k/15k = β, where

14k=first-order reaction rate constant of the conver-

sion of the 14N isotope substrate to product and 15k

the same constant for the 15N species. Shearer et al.

(1974) used a value of β of 1.005 for the incorpora-

tion of ammonium ion into microbial protoplasm and

1.025 for nitrification (Delwiche & Steyn, 1970). For

a similar model describing ammonification, microbial

assimilation of ammonium and nitrification, Herman

& Rundel (1989) used values of β of 1.0046, 1.0046

and 1.0176 for these three transformations, respect-

ively. Handley & Raven (1992) have cited values of

β for NH+ assimilation of between 1.012 to 1.020, 4

and for nitrification of between 1.015 and 1.035.

Good papers usmmarizing:

Use of the 15N natural abundance technique to quantify biological nitrogen fixation by woody perennials. Boddey et al 2000.

Measurement of Nitrogen Fixation by Soybean in the Field Using the Ureide and Natural 15N Abundance Methods' Herridge et al 1990.

One culture method will NOT capture the entire N cycle process. This is because not all components of N cycle are driven directly by microbes (for explanation sake I have highlighted different N cycling processes). For example ammonia volatilisation is driven by chemical conditions (e.g. soil pH) or enzymes (in case of urea the enzyme is urease).

As other colleagues suggested even if one is able to quantify microbes, the number of microorganisms may not to be directly proportional to the extent of any N cycling process. For example number of nitrifiers in soil (Nitrosomans spp and Nitrobacter spp) may not be directly related to the extent of soil nitrification. This is because there non-microbial factors that could dominate the nitrification process.

Biological N fixation by legumes can be quantified (plenty of literature available on this matter). On the other hand, N mineralisation of organic-N (or ammonification) process can be quantified by soil incubation methods (e.g. anaerobic incubation). Alternatively the ammonifiers (mainly heterotrophics) could be cultured.

Denitrification process (NO₃ to N₂O and N₂) is driven by denitrifiers and these are heterotrophs and hence could be quantified. But since denitrification process is also driven by other factors such as level of nitrate, level of electron donor such as dissolved organic carbon and anaerobic/anoxic condition, the extent of denitrifcation will not be related to the amount of denitrifiers present.

Immobilisation of ammonium is driven by heterotrophs and hence could be quantified. But immobilisation will also rely on available C and ammonium hence microbial numbers may not relate to the extent of the immobilisation.

The other component of the N cycling involves plant uptake of N which is not related to microbial numbers. Also N input from fertilisers or animal excreta are also not related to microbes. Equally N leaching (NO₃) from soil is not directly caused by microbes. So as ammonium fixation in soil is not driven by microbes (driven by clay mineral types).

Hi Bhavana Arora ji; Following links may be useful to you.

Thanks

I am also going to recommend a really good book on NItrification 

Ward, Bess B., Arp, Daniel J., and Klotz, Martin G., eds. Nitrification. Washington, DC, USA: ASM Press, 2011. ProQuest ebrary. Web. 12 September 2014.

But a short answer...

Nitrifying organisms obviously contain membrane bound enzymes to oxidize ammonia to nitrite, while other organisms will further oxidize nitrite to nitrate. The first step in the catabolic process is a protein super unit called the ammonia monooxygenase (AMO). This structure converts NH3 to NHOOH (hydroxylamine) and is substrate specific, in other words it can not process the Ammonium Ion (NH4+), this is one of the many reasons that soil pH has an effect on soil nitrogen cycles (with the caveat that there has been reported Archaea that are capable of utilizing NH4+ (although the mechanism is still unknown at least to my knowledge). But I would take at that book.

hope that helps a little 

For the new nosZ group, two related publications:

In Nature Climate change

in ISME J

Dear Natalia,

First of all  study the local flora of the place where you are planning to work. As native plants need less effort to establish and have less impact of local climate on their growth. Make list of plants then we can make out which could be best according to the suitablity of your place. If you are planning to construct wetland then Eicchornia have great potential to accumulate nitrogen and after harvesting it can be used in biogas plant as well for the production of manure. In my native place people are using it in biogas plant and organic manure formed is being used by farmers. Cyperus and Typha  are also good options.

Any newer synthesis would have cited this:

Cleveland, C. C. et al. 1999. Global patterns of terrestrial biological nitrogen (N2) fixation in natural ecosystems. Global Biogeochemical Cycles 13(2): 623-645

I agree with the the first step being to make a complete Nitrogen balance in the reactor. But I don't understand how you can measure a TKN as 1 mg/l and a total N of 20? Normally, all organic N forms including bacterial by-products as EPS are taken in account by the TKN (Total Kjeldahl N method = strong boiling acid digestion with selenium as catalyser). So if you get such a high total N in the effluent of a MBR, this N must be a soluble form resilient to digestion - and such forms are very unlikely in an urban sewages... What are the methods you use for TKN and Total N?

Well its a known fact that cyanobacteria can fix nitrogen. But in eutrophic waterbodies they have to compete with other algal species to bloom. At this stage, cyanobacteria can not risk to loose their energy in Nitrogen fixation, rather they use the available nitrogen source to increase their biomass rapidly.

Soil microbial biomass N (in form of organic N but not NO3 or NH4) is usually 1-2% of total soil N pool (the biggest one is soil organic N, contains above 90% of total N). But it has very high ecological value since the turnover rate is very fast. It is therefore very important to estimate not only the pool size but also turnover rate.

No, nothing happens. We did many tests and different concentrations of HCl and we found no effect on total N.

You could determine the gene abundance of denitrifiers by Q-PCR, targeting either DNA or RNA. You can get information about Q-PCR of denitrifiers from estuarine sediments in this article:

Smith et al, (2007), Diversity and abundance of nitrate reductase genes (narG and napA), nitrite reductase genes (nirS and nrfA), and their transcripts in estuarine sediments. Applied and Environmental Microbiology, 73(11), 3612-3622.

Bente's point is important - we can't neatly separate N availability from water availability. Another point of interaction is that Nitrate-N uptake is largely a function of mass flow, that is the movement of water through the soil toward the roots (driven by transpiration) carries NO3 to the roots. So in drier conditions N mobility may be more limiting.

We are investigating C dynamics a false time series along a land use transect in Southern Amazonia (www.carbiocial.de). I wouldn't call tropical ecosystems N-rich. Usually, there is a limited amount of N in the game, and only the fast turn-over rates keep most consumers satisfied. As soon as forest is cleared and root uptake from larger depths is reduced because of missing trees, N starts to leach out of the system. If the land is turned into grassland, litter fall is almost comparable to a forest ecosystem. If turned into agriculture, C input is reduced and so the capability to store N in organic substances slowly decreases. Fertilised N rushes through, as most tropical soils have a limited CEC, and also anionic N fixation is limited due to the positive surface charge of the soils rich in sesqui-oxides. Tropical soils under agricultural land use are often high in SOM (~3%), but a large fraction of it is recalcitrant and does not release large amounts of N. N mineralisation of less than 100 kg N ha-1 are typical.

Hope that triggers a nice discussion.

I agree, Milli-Q works best. When going on research cruises, we would take Milli-Q water with us in 10l carboys and then filter it again on board the research vessel using a bench top Milli-Q system (Millipore). Also, very important are thoroughly rinsed tubes for standards and samples. We soak 50ml Sarstedt/Falcon tubes in 1% HCL for at least 24h, then rinse the tubes with Milli-Q multiple times. You can reuse the tubes, they actually 'improve' over time. Only those in which you measure very high concentrations I recommend to discard. For the standard series always use the same tubes. Further, let the OPA age, at least 1-2 weeks. Always fix samples/standards immediately and wear gloves at all times.

There is another diffusion method for 15N-NH3 where you buffer your sample with MgO to a pH of 9.5 to 10, which also converts the NH4+ to gaseous NH3 which can then be captured on a filter as ammonium sulfate. The filter is acidified beforehand with Sodium Bisulfate, and is made into a "filter packet" that floats on the aqueous phase. Diffusions last from 3 to 10 days depending on the concentration of ammonia, and the filters can then be dried and analyzed via EA-IRMS. Make sure to preserve your samples at pH2 with H2SO4 to prevent any loss of NH3 beforehand (although freezing also works). volatile organic nitrogen compounds can be a problem though

Thank you Nityanand for the immediate reply.

Sorry - here's the other paper. Also anything by Jon Zehr will be worth your while looking at.

Cheers

Clare

Thank you very much Fulvio Rivano

I need more help in this area.

You need to run 2 standards, 1 control, 6 to 10 samples, one control, 2 standards sequence. As previous authors noted, you need to chose the correct standard for your samples (“same” chemical composition) and you need also to have your isotope ratios between the two standards. Closer your standards are to your sample the better result you get. The second problem in IRMS (but generally in spectroscopy) is the memory effect. You can measure 10 times one sample and make a plot, having on X axis the sample sequence and on y axis the measured values. Then you can see how bad the memory effect is. Just as a caution. The memory effect depends on the value of the previous sample. Less memory effect you get if there are no big variations between samples.

Just back from holiday... Thank you all for your new answers!

Nikos, do you know any publication about the nitrogen content of those mine waters you mentioned about? Can you say what is the estimated concentration or load of total nitrogen or nitrate resulting from those explosives?

Based on the answers I have gotten, I think that there is a very limited amount of research conducted on nitrogen loading from explosives and their impact on runoff quality.

Total plant nitrogen analysis by near infra-red spectroscopy is a quicker and efficient method compared to Dumas method of estimation and it is inexpensive. An attached research papaer on Total plant nitrogen analysis by near infra-red spectroscopy is enclosed for ready reference