Biological/ physiological responses and interactions of macros and trace elements - The Planted Tank Forum
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  • 2 Post By Mattymo92
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post #1 of 10 (permalink) Old 12-30-2015, 06:23 AM Thread Starter
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Biological/ physiological responses and interactions of macros and trace elements

Hello,

I have done a few searches and haven't seen this specific info on the forum (please send me a link if I missed something and it has been covered), but I was hoping some of you knowledgable hobbiests could help me better understand the chemistry of dosing fertilizers in my tank...

Could any of you help me understand how the macros and trace elements are actually used by the plants in my aquarium? What are the function of the specific nutrients once absorbed by the plants (and animals if fauna if they benefit from it)?

Just like with my own nutrition, in order to make appropriate decisions I think it is important to understand what a nutrient does rather than just whether or not I need it based on malnutrition symptoms.

Thanks for any info you can share!

Thanks,
Matt M.
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post #2 of 10 (permalink) Old 12-30-2015, 06:46 AM
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Hiscock's Encyclopedia of Aquarium plants outlines a lot of macros and trace elements uses in the aquarium. If you can find a copy, I highly recommend it.
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post #3 of 10 (permalink) Old 12-30-2015, 06:24 PM
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It can be very interesting to do the research you are looking for, but if you are not into the science of it, and just want to succeed with a planted tank, you can just dose the tank per https://www.plantedtank.net/forums/11...-regimes_.html and you will have the best chance to succeed. It is an individual choice as the which road to follow.
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post #4 of 10 (permalink) Old 12-30-2015, 11:01 PM
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Diana Walstad's book Ecology of the Planted Aquarium goes into this in much greater depth. Here are a few basics:

Plants use most. These are not thought of as fertilizers:
Hydrogen (H), Oxygen (O), Carbon (C).
We can supply carbon in the form of carbon dioxide (best), or liquid carbon products (work well for many plants, not all). Some plants (roughly half the plants we grow in aquariums) can get the carbon out of carbonates.

Fertilizers plants use the most. These are called macros:
Nitrogen (N)
Phosphorus (P)
Potassium (K)
In a packed fertilizer the three numbers on the package are the % by weight of these three materials.
Fish food has a fair amount of N and P. It does not have much K.
We can add fertilizer with these elements such as KNO3 (supplies potassium and nitrogen), KH2PO4 (dosed in low levels, so that although it has some potassium it does not count for much) K2SO4 (supplies potassium and sulfur).

Fertilizers used at rates somewhat less than the macros, these are secondary nutrients:
Calcium (Ca)
Magnesium (Mg)
Sulfur (S)
Ca and Mg can be supplied by the water if the GH of the water is over about 3 German degrees of hardness. Plants use these 2 in a ratio of about 4 parts Ca: 1 part Mg. If there is any doubt about there being enough of either of these, they can be found separately (Calcium chloride, magnesium sulfate and other materials) or in combination such as GH booster. Usually fish have a specific range of GH where they thrive. I would make the water suit the fish while maintaining a 4:1 ratio between Ca and Mg.
Fish food is somewhat low in Ca and Mg.
Sulfur is a common ingredient in most fertilizers. Many of the minerals in fertilizers are in the sulfate form, such as potassium sulfate or magnesium sulfate.

Minerals used in lower levels, referred to as trace or micros.
Iron (Fe) is the one that many people will add separately. Usually a chelated form. Chelation means the mineral is locked up in a molecule that plants can get into, so the mineral remains available to the plants, but is not available to get into combination with certain other minerals.
Fish food is somewhat low in iron.
All other minerals (roughly a dozen) are used in such small amounts they are generally lumped together. Fish food usually has enough of all of these.

_____________________________________________

In a low tech tank, or high stocking levels, where you are adding a lot of fish food and the plants are not using up the nutrients from fish food (digested by the fish, or rotting in the substrate) the test results before adding any fertilizers will show rising NO3 which you do water changes to keep low. Under these conditions you may assume the P and traces are just fine, too.
If the GH is OK from the water, then I would simply dose carbon, potassium and iron. And keep up with the water changes.

In a high tech tank, or low stocking levels, where you are not adding very much fish food, and the plants are pretty much using up all the nutrients from fish food, then the NO3 test will show it does not rise very much, and may simply maintain 0ppm.
Under these conditions you may assume that the plants are also going to be needing all the other nutrients.
The Estimative Index is one method of supplying all the nutrients that plants need in the ratios they use. It is based on supplying all the nutrients in a slight excess, then doing a big water change once a week to remove the excess.
PPS-pro is another method using similar ratios of each nutrient, but at much lower levels, not demanding a big water change.
Seachem makes a complete line of fertilizers with each bottled separately so you can customize the dosing for your tank.
There are other methods, too.
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post #5 of 10 (permalink) Old 12-31-2015, 05:38 AM Thread Starter
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Wow some great replies here! Thanks for the dosing advice Diana! Hoppy and Ichythyogeek, thanks for the links and resources! I will definitely do some researching with these.

Does anyone know what exactly these vitamins, minerals, and elements actually DO once inside the plants? As in... If in humans, glucose is converted into glycogen and then into usable energy within the human body and protein is broken down into amino acids and then used to build muscle and repair tissues within the human body.... What would be the equivalent of this be in plant physiology? What does Iron actually DO for the plant? WHY do my plants need Potassium and why do they begin to turn yellow if they don't have it? Why is phosphorus needed? How do all these things interact with the plant and each other?

Basically, for me understanding the why behind things always makes the overall picture much easier to understand since now it's a tangible thing in my head instead of just an equation or parameters to stick in... I'm sure others would benefit from this too. Does anyone have this type of knowledge that is willing to take time to share?

Thanks!!
Matt Morgan
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post #6 of 10 (permalink) Old 12-31-2015, 05:55 AM
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The answer to that is more of a complex course in botany, but here is a very simplistic list of which element does what in plants. This is not an extensive list by any means, just a bare scraping of the surface of this subject.

Hydrogen, oxygen and carbon become structural parts of plants, carbohydrates, sugars, lignins, cellulose and all other plant structural parts. Water is the carrier that transports everything between roots and leaves.

Nitrogen becomes part of proteins.

Phosphorus is part of the energy system of plants.

Potassium plays a part in the exchange of nutrients and charged atoms and molecules in and out of the cells.

The other elements appear in various proteins, enzymes, and many other chemicals in the plants. Magnesium, for example is found in chlorophyll.
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post #7 of 10 (permalink) Old 12-31-2015, 06:18 AM
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Calcium-helps form cell wall structures, activates enzymes.
Magnesium-activates enzymes that make lipids, central atom in chlorophyll
Phosphorus-energy transfer(no idea what this means, probably something in an energy cascade within the cell), part of enzymes, part of TGAC(DNA/RNA stuff)
Potassium-protein synthesis, stomata use, lots of stuff.
Sulphur-amino acids (therefore protein), chlorophyll
Trace elements: basically enzymes.

^^^large paraphrases from Hiscock's Encyclopedia.

I'm with MattyMo here. Although I'm not a fan of cellular biology, this seems fairly interesting from more of an element standpoint than last year's AP cellular-centric biology...

So many fish to keep, not enough aquaria.
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post #8 of 10 (permalink) Old 12-31-2015, 06:20 AM Thread Starter
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Thanks Diana! Very helpful!

And now you've also given me an idea of where to look for more info... Botany resources rather than planted aquarium sites.

Thanks,
Matt M.

Bump: Thanks Ichthyogeek!
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post #9 of 10 (permalink) Old 12-31-2015, 08:06 AM
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Plant's mineral nutrition

Quote:
Originally Posted by Mattymo92 View Post
And now you've also given me an idea of where to look for more info... Botany resources rather than planted aquarium sites.
Hobbyists are rarely interested in such details. You do best looking for "plant physiology" or "mineral nutrition" books like this one:
MARSCHNER, Petra. Marschner's mineral nutrition of higher plants. 3rd ed. Amsterdam: Academic Press, 2012, xv, 651 pgs. ISBN 978-0-12-384905-2.

Look especially for the transportation of nutrients: passive vs. active trasport. In general, the uptake and transport of nutrients in plants works in such a way, that for the plant to be able to uptake any nutrient, it needs first to "excrete" another nutrient. So it's a matter of exchange. In most cases, the plant excretes H+ ions (by a special apparatus called H+ pumps or specialized transmitters), and in exchange it receives other nutrients needed like K+, Ca++, Mg++, Fe++, but also PO4---, NO3- etc. Some simple ions (like K+, Ca++ etc.) don't need special transmitters to get into the plant cell. They use a simple diffusion (passive transport) for their move into the cell. Other ions (like PO4--- or NO3-) are too complex, and thus need the help of a special transmitters to get into the cell. This kind of uptake is called active transport, because for it to happen it needs some active energy.

The more you get into this, the more complicated it gets. So be prepared for some science.
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post #10 of 10 (permalink) Old 01-03-2016, 02:27 AM Thread Starter
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Great info! Thanks Marcel!
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