- Oxygenation prevents an excess of soluble iron entering the plant.
(Too much iron is just as bad as too little: too much iron causes
heavy metal poisoning.)

So they use O2 as a gate keeper to prevent excess nutrients from
coming into the roots? That sounds awful speculative at best. I have
done work on Spartinia and some other marsh plants that deal with
anaerobic substrates, salt level gradients. I don't buy this agrument.

- Roots need oxygen just as the rest of the plant does. Oxygenation
of the roots during the day helps the roots respirate during the night.

Roots need O2 all the time.

- Bacteria use oxygen to oxygenate H2S, which is toxic. The root
oxygenation protects the plant against a substrate that's gone too
anaerobic.

(Plants absorb phosphate preferentially
through the roots (depending on the plant, 60% to 99% of
phosphate enters the plant through the roots, even if the water
contains an ample supply of phosphate).)

No they don't, they will perferencially absorb PO4 right through their
leaves and stems. Reference: The journal Freshwater Ecology Feb 2000,
distilled: Aquatic plants(a large cross section of common aquatic
plants, not just one or two) will take in nutrients from the water
column if enough is avaiable.
When there is not enough PO4 or NO3 in the water column, they will
allocate more uptake from the roots if there is a source of nutrients
there but not in the water column.
Basically why transport nutrients, if you can get them right where you
need them?
You can also see this in your tank by trying to add a PO4 source to
your gravel versus adding KH2PO4 to your water column.
You'll see immediate(within an hour or less) plant responses from
this.

I think this notion you are making here is valid IF you have an
environment where there is little PO4, NO3 etc in the water column,
but if you test the water column with adequate supply of dissolved
nutrients, the roots don't need to take in the nutrients and transport
them. Plants will take the nutrients where they can get it. But if you
don't test the other side of that coin, one can draw the incorrect
conclusion(s).

- Root oxygen provides an aerobic enviornment for symbiotic fungi
that help the plant's nutrient uptake.

There has been some interesting work done very recently on fungi in
aquatic plants. I've found ecto mycorrhizae on Bolbitus
rhizomes/roots.

They aid in denitification (turning NO3- into NO2-) and
help to keep manganese in sulution as (Mn2+, at +396 mV) and
help to keep iron in solution (Fe2+, at -182 mV). The denitrifying
aspect of anaerobic pockets seems to be the most useful aspect
of a soil substrate (because I can easily add Fe, K, Mn, and so on
with fertilizer).

NO3=NO2? Plants don't use NO2. They convert NO3 at their cell's
chloroplast membrane to NO2 and then very quickly(this way it cannot
cause damage) into NH4 but NO2 is toxic to plants anywhere else in a
plant.
You can also try this out at home in a heavily planted tank.
Try fishless cycling in a fully packed plant tank.
The NH4 will decline, the NO2 will appear and the persist for 2-3
weeks, even with a fully planted tank and no outside sources of N
being added.
If plants used it, why aren't they? Simple, they don't use it.

See above -- Krause also recommends soil and peat substrates,
also quoting anaerobic processes as being desirable.

I've found examples where this is not true in nature and in my tank.
Plants are very adaptable and dependent not simply on the substrate
and their roots systems but the water column as well, which is much
easier to test for and measure concerning uptake rates and plant's
needs.

Right. Very slow flow, so you are not constantly flooding the roots
with oxygen, but you keep the substrate sufficiently aerated to prevent
the bad anaerobic stuff (H2S) from happening. Walstad quotes evidence
of reduced plant growth with substrates that are too oxygenated.

But......there's this issues once again, if the plants are supplied
with enough water column nutrients, then the substrate doesn't matter
much if at all except for a mechanical support for attachemnt. You
cannot ignore this issue when addressing aquatic plants. It fouls your
conclusions and data a great deal.

The
high-throughput under-gravel filters of the past were great plant killers.
(I never used one myself, but I've had plenty of conversations with
other aquarists who keep telling stories of weekly trips to the LFS to
replenish dying plants...)

I think traditional one did so so.
I use a RFUG grid of tubes like on pg 15 of the Rataj/Horemannii Book.
This worked as well as any plant tank I'd seem until I saw some
Amano's work.
I also wanted a simpler to make substrate and felt there could be a
nice balance between water column and substrate uptake. Why not have
good levels in both places?

Right. I'm sure that's why flourite is considered a good source of iron
because those anaerobic pockets would help to keep the Fe in solution
so the plants can get at it.

Yes, I tend to feel this way, although I'm not certain, just
speculating (as usual.

Well, it depends on the nutrient: phosphate is taken up preferentially
through the roots, ammonia is taken up preferentially through the leaves.

See above, I have not found the first part to be the case at all.
But the second part is true.

I'd probably make it two tanks in a controlled experiment because,
with a single tank, whatever leaches out of the soil substrate might
affect the non-soil part of the tank and ruin the control. It really
would be interesting to try this. But I don't have the room or inclination
at the moment to set up two tanks just to find out why the one I have
already is working so well :-)

I have 8 tanks just for such a test. But it'll be a year or two before
I get to anything like that.

The combination of lots of variables in the right
proportion is probably more important than the level of any single one
of them.

Yep, you got it.
But the relative effects of each vaiable is what is needed to be
considered.
I'm saying you'll get better growth, if you use both a good water
column dosing routine(including macro nutrients) with a decent
substrate. The water column is more important than the substrate in
CO2 enriched tanks with higher growth rates.
In non CO2 tanks, this can be true as well but more focus is shifted
to the lower maintenace and slower growth rates which will lend more
need for a good substrate supply of nutrients.
Also, dirt wears out after awhile. No nutrients left. But you can
freeze soupy soil in ice cube trays and push these down under neath
plants etc.
Or clay balls mixed with dirt.
I'm more partial to peat myself.

Most of the crypt pictures I've seen show crypts growing in mud. Yes,
there is often a sand or gravel layer near the top but, as soon as you go
down an inch or so, the substrate is full of accumulated organic material.
(All that leaf litter has to end up somewhere...) Krause has some interesting
illustrations of soil cores taken in various habitats. From memory, pretty
much all of them turn into mud a few inches below the surface at the latest
(and plant roots seem to extend into the mud most of the time).

I buy this.

I'm waiting for my digital underwater camera to try out next week.

I'm envious! :-)

Try looking on ebay, I got mine for 36$ including shipping.
It's only 640 x 480 but that's fine. Has a flash also.


Yes. But I'm still unsure about how I would get anaerobic zones
in fluorite.

Recall each grain of flourite or kitty litter etc is a highly porous
structure.
The internal micro habitat is anaerobic or close to it.

I tested plain old gravel with laterite vs flourite and considering
the make up of each(we had them analyzed by a lab), the physical
stucture was the only real difference I could come up with of why one
did/does better.
The flourite can also be moved around, disturbed etc.

Due to the micro habitat being preserved in each grain, there's not
need to worry about disturbing a larger "macro layer" although some
does form in flourite onyx sand substrates. Just not nearly as a
dependent issue I think.

It seems that it is far too coarse for those to build up.
Maybe the micropores you mentioned are the real secret: you'd
end up with anaerobic areas inside the flourite without having
the mess you get with soil or peat. I honestly don't know...

That's my guess.

I might do that for my next tank. Despite having harped on about how
great peat is, I still don't like the mess it makes when I pull up a plant.
More fluorite and less peat would obviously make less of a mess.

Well there's only a small amount and it is added only the very bottom
layer.
Amano's substrates, the Powersands, have peat covered light weight
clay rich high surface area grains.
I use something like Scott's ground peat, no loose moss etc.
Taste great on Chicken:-)
Regards,
Tom Barr


Cheers,

Michi.