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Nitrate reductase activity in roots and shoots

Discussion in 'Articles' started by paludarium, Jan 9, 2011.

  1. paludarium

    paludarium Guest

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    Hi,

    I don't know if it was discussed here before. Recently I read an article "Nitrate reductase activity in roots and shoots of aquatic macrophytes". To my surprise, the author found that root NRA(nitrate reductase activity) exceeded shoot NRA in 11 out of 17 specimen. Does it mean that the main sites of aquatic plants to uptake NO3 locate in the roots instead of shoots? Or NO3 was transported from shoots to roots for the reduction process? BTW, the study also indicated that 500 μM NO3 showed a 2-17 fold increase in both root and shoot NRA compared to ambient NRA. Well, 500 μM NO3 is about 31 ppm NO3. So....we have to dose more NO3?:confused:

    Regards,
    Erich
     
  2. Biollante

    Biollante Lifetime Charter Member
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    N Fixation Isn't As Easy As We Plants Make It Look

    Hi,

    For those not having Athens or institutional privileges or US$37.95 :eek: the article is available in PDF form http://www.vliz.be/imisdocs/publications/57400.pdf. :)

    It appears the reason we dose higher levels of NO3 then often found in nature, yes. ;)

    It would seem, off-hand anyway that in NO3 deprived areas the roots are the primary source for N accusation and fixation. :confused:

    Biollante
     
  3. Tom Barr

    Tom Barr Founder
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    Well, it means there's more in some plants found in the wild, but cultured plants will add NR where it's needed and reduce the amoutns needed elsewhere.

    Plants have consitutive NR(always present) and then a lot of inducible NR depending on the given situation in the environment.

    So we cannot make a lot of conclusions other than WHERE the plant sin question where taken from and what they where exposed to.
    Molecular methods can answer where and what type of NR, but this is done for crops and plants of economic importance generally.

    In many siutations, the roots have the best source of nutrients, in say a nutrient rich Danish steam?
    Both.

    In other systems, mostly the water column, eg Florida springs.
    So you can sort of predict where the highest level of NR will be in each system.
    You also NEED to compare relative rates of growth, some a weedy plants and high extremely high growth rates, whereas others are painfully slow growers.

    This will make a huge difference in the comparative value.

    Yes, plants can tansport reduced N most anywhere it needs.
    So the inducible system has a 2-17X increase, the constituive is present however as well.

    Hoagland' solution is typically about 235 ppm N.
    So it's pretty rich.

    Plants will grow well at lower levels obviously.
    I'd not worry too much about it.

    I read that paper some years back, both researchers are excellent.
    They also wrote the one that suggest sediments and water column have no effect if the ppm's are rich enough in either location, even when the roots where cut off in 4 species.



    Regards,
    Tom Barr
     
  4. paludarium

    paludarium Guest

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    Thanks Tom,

    the author also discussed that factors such as presence of NH4, temperature, light and carbon availability will also influence NRA. Well, the presence of NH4 is of my interest. An example from the author, NH4 concentrations in bulk water above 2 μM (about 0.036 ppm) impeded the Myriophyllum spicatum uptake of bulk water NO3 (24 μM, about 1.49 ppm), the NH4 level is practically not likely to be found in the planted tanks, especially with good filtrations. Correct me if I am wrong in the equivalences. Maybe it is not NH4 but NO3 that aquatic plants really absorb in our tanks.

    Regards,
    Erich
     
  5. Tom Barr

    Tom Barr Founder
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    Know of anyone that measures NH4 much an also measures it 0.036ppm?
    That's lower than any test method used in the hobby. This assumes that they actually calibrate the test kit as well(never met one that did this for NH4 to date-15 years of looking).
    Also, fish food and feces likely adds more than this daily to many systems, particularly my own since I actually have a sizable fish load in my tanks and also add 30-45ppm of NO3 per week.

    I think plants do both NH4 and NO3, NO3 is used as a counter balance to K+ in the vacule for stoarge, NH4 is not store as NH4, only as amino acids etc since it is highly toxic at high levels, whereas NO3 is not.
    Best to nab both forms of N and use both forms but in different ways.


    Regards,

    Tom Barr
     
  6. paludarium

    paludarium Guest

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    Hi Tom,

    both NH4 and NO3 have been bothering me for a long time, not for the algae issue but the plants issue. In her article "Plants and biological filtration", Diana Walstad demonstrated a diagram showing that aquatic plants preferred NH4. However, you interpreted it in another way: aquatic plants begin to absorb NO3 when NH4 level is below 0.5 ppm and they stop uptaking NH4 when the level is too low, say 0.1 ppm. This comment really impressed me.

    Well, most researchers carried out their the experiments at high levels NH4 that were toxic to many, if not most, of our aquarium critters. I wonder whether our aquarium plants have chances to absorb NH4 at low levels such as our aquarium environments. Reddy et al in their study "Nitrification-denitrification at the plant root-sediment interface in wetlands" found that O2 was transported to the root zones of aquatic macrophytes and supported nitrification of NH4 in aerobic rhizosphere. Also as showed in fig.1, NH4 was transformed to NO3 in aerobic rhizosphere before absorbed into the roots. There were competition for NH4 between nitrifying bacteria and plants roots. Will hight nitrate reductase activity in roots be an indirect evidence? :confused:

    Nitrification also occurs in the epiphytic communities on other macrophytes surfaces like leaves and stems, where O2 is more abundant. I don't know how fast could NH4 diffuse into the plants tissues, especially at low levels. There are always competition between plants and bacteria, everywhere on the plant surface. I speculate that in our aquarium with filtrations aquatic plants absorb NO3 but not NH4, irrespective of their preference.

    I am no scientist, but only with some imaginations, need more help from the experts. Thank you.

    Regards,
    Erich
     
  7. Tom Barr

    Tom Barr Founder
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    Now for the rest of the story, WHEN do the plants add the O2 to the sediments?
    During the day, so how long afte rthe sun goes down or the lights are turned off does this stop?

    Some suggest a few minutes, as in 5-10minutes.

    So what happens to all that free O2?
    It's gone and bacteria have used it up, now the sediment is going back towards the anaerobic side.

    We could label the NH4 and the NO3 and use stable N15 to see who gets what, including algae for that matter as well.
    This way we could track uptake even if it is transformed from 15NH4+ into NO3.

    We also could label O2 and track the stable isotopes of that as well.

    A bit advanced methods, but fairly straight forward.

    I think there's not much yield differences in aquatic plants since they are often limited by other nutrients, including NO3 and NH4.
    So under a limiting situation, NH4 would be worth much more to a stressed plant than say NO3 perhaps.
    If you buy ferts by the ton, this can mean a fair amount of $$ cost difference.

    But if everything is non limiting, I think it matters less.
    Cost of ferts is not much concern for hobbyist.

    Also, make sure you realize most studies are for one plant under a certain set of the conditions, it is not wise to assume that such results can be applied to all 300-500 species of plants we keep.
    You can make a weak case for some preference, but I think it is weak based on aquarist results.

    If you want low levels of NH4, simply add more fish.
    It is much better "natural dosing" and the dosing "method"(keeping fish in aquatic plant tanks) is part of the hobby after all.

    Regards,
    Tom
     
  8. Tom Barr

    Tom Barr Founder
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    Now for the rest of the story, WHEN do the plants add the O2 to the sediments?
    During the day, so how long afte rthe sun goes down or the lights are turned off does this stop?

    Some suggest a few minutes, as in 5-10minutes.

    So what happens to all that free O2?
    It's gone and bacteria have used it up, now the sediment is going back towards the anaerobic side.

    We could label the NH4 and the NO3 and use stable N15 to see who gets what, including algae for that matter as well.
    This way we could track uptake even if it is transformed from 15NH4+ into NO3.

    We also could label O2 and track the stable isotopes of that as well.

    A bit advanced methods, but fairly straight forward.

    I think there's not much yield differences in aquatic plants since they are often limited by other nutrients, including NO3 and NH4.
    So under a limiting situation, NH4 would be worth much more to a stressed plant than say NO3 perhaps.
    If you buy ferts by the ton, this can mean a fair amount of $$ cost difference.

    But if everything is non limiting, I think it matters less.
    Cost of ferts is not much concern for hobbyist.

    Also, make sure you realize most studies are for one plant under a certain set of the conditions, it is not wise to assume that such results can be applied to all 300-500 species of plants we keep.
    You can make a weak case for some preference, but I think it is weak based on aquarist results.

    If you want low levels of NH4, simply add more fish.
    It is much better "natural dosing" and the dosing "method"(keeping fish in aquatic plant tanks) is part of the hobby after all.

    Regards,
    Tom
     
  9. paludarium

    paludarium Guest

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    Hi Tom,

    in the study "Nitrification and denitrification in the rhizosphre of the aquatic macrophyte Lobelia dortmanna", Nils Risgaard-Petersen and Kim Jensen found that O2 was released from the L. dortmannna roots to the surrounding sediment both during illumination and in the darkness. The authors used 24:24-h L/D diurnal cycle in the experiment, but not the regular 12:12-h L/D. Free O2 was still present in the Lobelia sediment at the end of a 24-h dark period.

    The authors also concluded that it may seem paradoxical that by stimulating coupled nitrification-denitrification activity via root O2 release L. dortmanna introduces bacterial competitors for inorganic nitrogen in the rhizosphere and thus indirectly reduces its own potential nitrogen supply.

    Lobelia dortmanna probably is not an excellent material and should not represent hundreds of aquatic plants. However, if aquatic plants absorb plenty NH4 directly from their roots, why do plants still need nitrate reductase in the roots, and the root NRA(nitrate reductase activity) exceeded shoot NRA?

    Regards,
    Erich
     
  10. Tom Barr

    Tom Barr Founder
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    Who knows, they might have an evolutionary basis for having a lot of NR in the root systems.

    In general, more NO3 is there.
    In most studies I've seen, the plants stop adding O2 as soon as the light is off.
     
  11. Biollante

    Biollante Lifetime Charter Member
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    #11 Biollante, Jan 12, 2011
    Last edited by a moderator: Jan 12, 2011
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