Zapins

JeffyFunk Pmed me a series of very interesting questions the other day and I thought they were worth sharing with everyone since they seem to summarize a lot of the questions I've been researching and answering over the last few weeks. I still need to finish researching toxicities and appropriate ranges for micros but I think I have enough info to start wrapping up my findings.

I think Magnesium and iron are probably the major two micro deficiencies out there, followed by Boron.

The problem with magnesium deficiency is that the same symptoms can be caused by a toxicity of calcium, potassium and a few other micros that inhibit uptake of Mg. Mg is highly dependent on the ratio between K and Ca. If you have 1 Ca :2 Mg you will likely see toxicity and see a calcium deficiency. If you see 40 Ca : 1 Mg you'll see a Mg deficiency as Ca blocks Mg's uptake. Same with potassium, though potassium does not have as strong an effect as Ca or Mg which is why you can add substantially more K and not see problems. The research I've been seeing suggests that the K concentration should be higher than the Ca which should be higher than the Mg. Some says 4K : 2Ca :1Mg, others don't mention K and say 4Ca:1Mg. I think the key point here is that Mg should never be higher than K or Ca otherwise you'll get issues.

Iron seems to be needed in larger amounts by aquatic plants more than almost any other micro (except Mg). So yes Iron is a very important micro.

I would estimate that iron seems to be the number one micro deficiency people see in their tanks. Most people use city or well water that naturally has enough Mg in it so you don't see Mg as often.Furthermore, the Mg seems to be in an ok ratio with calcium so it doesn't normally cause issues. If you use RO water and reconstitute I'd pay special attention to Mg since it would have more of a chance to be depleted. Some research says 0.01 ppm is the lower range for Fe some prefer higher levels (around 0.1 ppm). This is non-chelated iron, like FeSO4 which is more toxic than chelated iron. Iron's (IC50) toxicity (dosed as FeSO4) was about 1.1 ppm for duckweed after a week or so. We use chelated iron so our toxicity threshold is likely a lot higher. I do not know how toxic ferrous gluconate is, it has never been talked about in the literature that I have read. One of the interesting things I read though, is that part of iron toxicity is blocking the use of sulfur in a plant. Sulfur deficiency also shows up as yellowing of the plant (low and new leaves) so perhaps that explains how some people see "iron deficiency" symptoms in their plants when they are dosing very high levels of iron regularly?

The other micros like Mn/Cu/B/Ni etc... are hardly ever deficient. The only time I've seen any sort of evidence that is probably due to one of these is when people mix their own fertilizers and don't add enough. Or possibly a few other unusual circumstances. That is why I suggested earlier in this thread that perhaps we really don't need to be adding a crap ton of micros but rather need to be adding iron separately in larger amounts. To give you an idea of what I mean, for the last month or two ever since I wrote that I've been dosing 0.6 grams of CSM+B in my 90g tank which has high light and CO2, glosso and stem plants and I have not seen micro deficiencies. This reinforces my belief that we really don't need a high concentration of most micros to grow healthy plants.

The limits for each of these elements is somewhat difficult to figure out. Not many studies have been done on heavy metal toxicity in aquatic plants. There are a few which I have posted earlier in this thread and a few more which I will post in this thread soon. For example, duckweed starts to show inhibition at about 0.15 ppm copper after a few days. I confirmed this with more than 3 studies they all agree at 0.15 ppm you see less growth. All studies used unchelated copper, some as copper sulfate others as copper chloride, none used EDTA copper like CSM+B use. The healthy level for copper in a planted tank is below 0.02 ppm for plants and below 0.015 for algae. Nearly instant death occurred when copper of above 1.1 ppm was used in all plants and algae. See this post for details on one of the studies I read and pictures of the duckweed dying: https://www.aquaticplantcentral.com/f...tml#post661246

Chelation matters, it matters a lot. I was reading other studies last night on copper toxicity using green algae (C. vulgaris), apparently one study found that inhibition started at 0.02 ppm CuCl, but another study used EDTA chelated copper and inhibition only started at 0.53 ppm Copper. So as you can see copper is roughly 26x less toxic when chelated. From what I have read the same is true of all other heavy metals. From: Toxicity of metals to green algae and Ceriodaphnia dubia: The importance of water column and dietary exposures by Sofyan, Agus. University of Kentucky, ProQuest, UMI Dissertations Publishing, 2004. 3130302.

Manganese is also quite toxic at low levels. At about 0.08 ppm it was found to be toxic to some aquatic plants. See: https://www.aquaticplantcentral.com/f...tml#post662078

Boron is fairly toxic as well, I will need to do more reading to get exact values for what it should be to prevent toxicity. This is some of what I have read about it if you'd like to read through it. https://www.aquaticplantcentral.com/f...tml#post660574

I'm having trouble with zinc toxicity. A lot of studies have widely varying levels for toxicity. Some say 8 ppm is toxic, others say 1 ppm, others say its not that toxic, some say it is toxic at 0.08 ppm, our results seem to say it is pretty toxic. So perhaps it depends on the species of plant and algae in question and the form of Zinc used (chelated or unchelated). I don't really have a good max value for zinc yet though judging by Cavan's plant troubles earlier in this thread I think it safe to assume a max zinc value should be below 0.1 ppm. See for the supporting papers. https://www.aquaticplantcentral.com/f...tml#post661246

To answer your other question what the most critical elements are and what concentration ranges they should be in. The research I've done does not have a good answer for what ratios micros should be in in relation to each other. Many researchers seem to think it doesn't matter as long as the micros are in low concentrations. If you add too much copper you'll get stunting, same with any heavy metal. There seems to be no proven benefit to keeping copper in a 1:1 ratio with zinc or a 20 Fe : 1 Cu ratio or any other ratio like that.

I think if you had a trace mix that did not include small amounts of the essential micro nutrients plants need you would probably eventually get a deficiency in a high light, CO2, stem tank. Maybe fish food and (non RO) water changes could get you by in a lower light tank with slower growers but not likely in a fast growing tank. If you look at a lot of trace mixes that scientists use for plant and algae experiments you will see they include all the micros in tiny amounts. I could probably have a look and post a few of their recipes if you are interested?

I will need to double check it, but I seem to remember that CSM added boron to its mix because some people were having issues without it. I'll have to look that up though since it was a very long time ago that they started adding B to the mix.

I'll finish my research shortly and write a formal post about all the findings and all the journals they came from so others can look through it all if they like.

Zapins

More interesting info:

Sulfate toxicity/Sodium toxicity:

Summarizing from this article:

• 200 ppm sulfate or lower is safe (for mosses at least - probably other plants).

• 1000-2000 ppm Na is damaging to plants (so 100-200 ppm and below is safe). See https://www.aquaticplantcentral.com/f...tml#post661176 for more info on Sodium toxicity

• Higher Toxicity <--------[ K > SO4 > Na > Cl ] -------> Lower toxicity

*Note*
The placement of Cl as least toxic comes from the sodium review by Hart on page 111 (see below for reference)
*Note*

It seems that sulfate is quite non-toxic to aquatic plants.

This study dosed sulfate as Na2SO4 from 0-1500 ppm and tested several parameters of growth using Fontinalis antipyretic (an aquatic moss). The study found that chlorophyll concentrations decreased in all sulfate dosed tests compared with the control (1.3 ppm sulfate). However, the chlorophyll didn't decrease significantly until after 200 ppm sulfate was added.

The study also described how it is the calcium in hard water that protects plants from higher concentrations of sulfate and heavy metals.

Another study done by Fragm (1975) found that 100 ppm of K2SO4 was harmful to the aquatic moss. This is apparently because the K ion was causing toxicity not the sulfate ion (as the study above found).

This study also states that freshwater macrophytes are generally tolerant of salinities below 1000-2000 ppm (Hart et al., 1991).

From:

Trevor D. Davies, Sulphate toxicity to the aquatic moss, Fontinalis antipyretica, Chemosphere, Volume 66, Issue 3, January 2007, Pages 444-451, ISSN 0045-6535, http://dx.doi.org/10.1016/j.chemosphere.2006.06.021.
(http://www.sciencedirect.com/science...45653506007594)
Keywords: Bryophytes; Sulphur pollution effects; Chlorophyll concentration; Water hardness

From

Article:A review of the salt sensitivity of the Australian freshwater biota
Author:Hart, BT
Journal:Hydrobiologia
ISSN:0018-8158
Date:1991
Volume:210
Issue:1
Page: p105

Zapins

Well since you have me thinking about Mn, Zn and Fe let me explain more about Mn deficiency.

Mn's Role
Mn's main role in photosynthesis is its involvement in the water splitting system of photosystem II. It is also involved in metabolic processes such as respiration, photosynthesis, synthesis of aminoacids and hormone activation. Mn is also used as a cofactor in an enzyme called superoxide dismutase which is an extremely important enzyme that helps stop oxidative damage caused by reactive oxygen species and other radicals that are made by photosynthesis. Therefore, when Mn is deficient it is dangerous for the plant because it affects photosystem II which provides the necessary electrons for photosynthesis and at the same time reduces the plant's ability to prevent damage by reactive oxygen species.

Mn Deficiency
Mn deficiency occurs most often when the pH is between 7.3-8.5, when the CaCO3 levels and organic levels are high. Also, chelated Mn is absorbed by plants more slowly than free Mn ions. Mn is an immobile nutrient, and therefore cannot be transported out of old growth so all effects show up on newer leaves (but not the very newest leaves).

Mn deficiency becomes unmistakable only when the growth rate is extremely slowed down. It shows up as diffuse interveinal chlorosis on young fully formed leaves (which differs from iron deficiency which shows up on the very newest small not fully formed leaves first). Severe necrotic spots or streaks may also form in Mn deficiency. Symptoms often appear first on the middle leaves. In mild cases the symptoms appear on young leaves and disappear as the leaf matures. Young leaves often show a network of green veins in a lighter green background, closely resembling iron chlorosis.

Interestingly, in contrast to iron deficiency the chlorosis from Mn deficiency is not uniformly distributed over the entire leaf and the leaf tissue may rapidly become necrotic.

It can be difficult to tell early Mn deficiency apart from iron deficiency, but late Mn deficiency leaves start dying rapidly and necrotic lesions develop.

Mn Toxicity
Mn can be extremely toxic to plant cells. Toxicity occurs mainly in acidic conditions with low organic content in the environment. Mn uptake does not appear to be tightly controlled.

Toxicity causes plants to slow down their growth rate, but you will also see interveinal and marginal chlorosis in older leaves. Necrotic leaf spots are also very common and so is leaf wrinkling. These symptoms can occur all over the whole plant (new and old growth) but in terrestrial plants is focused mainly in the old growth. Mn toxicity can sometimes appear similar to Fe deficiency due to the chlorosis. Toxicity of Mn is also made worse if other nutrients are in low concentrations (Ca, Mg, K, Fe), and in general higher Ca and Mg levels make micro nutrients less toxic and protect plants.

From:

Handbook of Plant Nutrition by Allen V. Barker & David J. Pilbeam

From:

Manganese as essential and toxic element for plants: transport, accumulation and resistance mechanisms, by R. Millaleo et al.,

Zapins

Iron Toxicity:

http://www.esd.ornl.gov/programs/eco...s/m5520ata.pdf

http://www.skepticalaquarist.com/ferrous-ferric