Overdosing non-aquatic plants

Discussion in 'General Planted Tank Discussions' started by Fred Dulley, 9 Sep 2008.

  1. Fred Dulley

    Fred Dulley Member

    Messages:
    512
    Location:
    Cardiff, Wales
    Hey guys.
    This isn't strictly about aquarium plants but I didnt know where else to post this.
    This came up in my alevel biology class today. The teacher said that too much potassium was bad for plants and it would suffer from it. I didn't quite understand this, seeing as we overdose our plants, and surely the amount of nutrients taken up by the plant would depend on the other limiting factors, most importantly light and CO2. If these weren't high enough to demand all of the potassium then how could the plant take up too much for it to cause a negative effect. She then answered that the potassium would be taken up by active transport and so the plant wouldn't be able to stop the uptake of potassium. I'm well confused.. can anyone shed any light on this?
     
  2. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    Location:
    Chicago, USA
    Hi Fred,
    I don't know the answer but I guess it would be easy to test. Definjitely in aquatic plants this is untrue. What does this instructor say are the effects of K+ overdose? Have there been experiments or results documented, and if so what level of dosing caused malfunction? Is it species dependent? How were K+ levels within the plant tissue monitored, i.e was the failed plant dried and it's K+ content determined? What type of analysis showed that the failure was due to K+ and not some other coincidental agent. What is the mechanism of the failure? In terrestrial plants K+ and Ca+ are used to control the stomatal openings so conceivably a K+ overdose might flood the guard cells and not allow them to close the stomata thus desiccating the plant. This wouldn't be possible in an aquatic environment but is a possibility in terrestrials. Anyway, these are the type of questions I would be asking.

    Get some KSO4 and dose the heck out of the plant and see what happens.

    Cheers,
     
  3. aaronnorth

    aaronnorth Member

    Messages:
    3,955
    Location:
    worksop, nottinghamshire
    Plants can take up more potassium than they need, and this is not toxic to the plant but if too much potassium is taken in, it can lead to magnesium or calcium deficiencies in plants.
     
  4. Fred Dulley

    Fred Dulley Member

    Messages:
    512
    Location:
    Cardiff, Wales
    Thanks for the reply Clive. :)
    Great questions to ask too but I doubt she is that experienced to answer any of them. It's probably something she's just been taught to believe. I still might take a copy of the questions in and ask the head of biology.
    A test sounds fun too!

    Thanks Arron, although I'm wondering how it could cause the deficiencie of another mineral..
     
  5. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

    Messages:
    8,952
    Location:
    Chicago, USA
    Yes, well that means failure due to Mg+ or Ca+ deficiency not due to K+ overdose. This just means that K+ was unlimited and Mg+ or Ca+ were limited. This is the standard deficiency mechanism. If this was indeed the failure then K+ should be dosed while ensuring Mg+ and Ca+ are also unlimited.

    Do the test yourself and report back. I forgot who it was a few months ago that was taking an exam where he was forced to say that phosphates cause algae - because The Matrix is programmed that way.

    Cheers,
     
  6. Fred Dulley

    Fred Dulley Member

    Messages:
    512
    Location:
    Cardiff, Wales

    Yeah, that was me and another member on here in the BYA2 exam.
    I have to say that the debates in biology got quite heated last year because of that haha. Much to everyone else's dismay (students) in my class.
     
  7. JamesC

    JamesC Member

    Messages:
    1,276
    Location:
    Bexley, Kent
    Potassium excess can cause problems with terrestrial plants with calcium and magnesium blocking. Other chemical excesses also can cause problems. Levels we have in planted tanks are generally relatively low but with soft water you can get problems if you're not careful. No doubt I'll get flamed for this suggestion.

    For info - http://www.finostrom.com.gr/images/fertilizers/map.htm

    James
     
  8. aaronnorth

    aaronnorth Member

    Messages:
    3,955
    Location:
    worksop, nottinghamshire
    I am not sure on the full explanation and i cant remember much as we just went over it last year and didnt go fully into it, i am sure a search will give you an answer.

    Excess Nitrogen can also cause the same problems. These are absorbed much quicker then calcium & magnesium, also, a more acidic ph can cause calcium deficiecies too. I think the K+ 'locks up' a process in the active transpotation procedure.

    like i say i cant remeber fully.
     
  9. Fred Dulley

    Fred Dulley Member

    Messages:
    512
    Location:
    Cardiff, Wales
    Thanks for all the replies guys. Can always count on the UKAPS forum.
     

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