Re: Roots/aerial roots

[Thomas Barr <tcbiii at earthlink_net>]

> Giancarlo (I think) asked about aerial roots in plants.  Speculation
> followed that substrate (as opposed to water-column) fertilization might
> help ameliorate this.  Tom responded with:
 
>> I think it's more likely a response to needing more O2 for root respiration.
>> Much like Cypress knees in swamps or Mangrove roots' allowing O2 for root
>> respiration. A number of wetland plants do this.
>> There's no source of O2 down in the wetland substrates.
 
> I agree with the assertion that there's no O2 down in aquatic substrates,
> save for in the mm or less around the roots of aquatic macrophytes [1].

Depends on the substrate type, grain size, organic content, flow rates.
Wetlands are mighty stagnant, organically rich muck.
But if you talk about something growing fairly clean large grain sand then
the layer will extend down further. You will find an inversely proportional
relationship with organic content/loading and aerobic depths. I'vbe found
some sword plants in deep sand but the roots made it down to the anaerobic
areas, almost 20cm inches down. I think in aquariums with no flow through
their substrates, say like flourite, often the main area of aerobic activity
seems to be about an inch.

But here's the hook: the individual grains have pore spaces that are very
small and many regions within each grain has internal spaces that are
anaerobic. You can pick them up and not disturb the internal conditions of
each grain much. The plant's roots will often bore right into these grains.
 
> The O2 is there, however, b/c the plants put it there.  Aquatic plants
> draw up CO2 from the substrate (CO2 that results from bacterial
> respiration made possible by the O2 the plants pumped out down there).
> Aquatic plants also draw up other nutrients from the substrate:  P, N, K
> and all the rest, but don't take them up nearly as readily from the water
> column as they do from the substrate [2].

Humm , I know Chamber's work and he's good.
I have a paper by Madsen and Cedergreen, Journal of Freshwater Biology(2002)
74, 283-291 that indicates that the RGR, relative growth rates or not one
but 4 common aquatic plants all were able to satisfy there nutrient demand
from the water column via leaf uptake. Removal of the roots have no impact
on the RGR of the plants.
Both the N and P concentrations in the rooted and the de rooted plants were
the same.

> Now, that said, I suspect that our mini-environments don't have much in
> common with the substrates in nature (if I may grossly generalize the
> substrates used in the hobby).  First, there are almost no nutrients down
> there in our gravel.

But we fertilize small amounts regularly to the water column.

> Certainly rock gravel itself possesses no nutrient
> value for plants, and what little may be present as detritus or
> particulate organic matter (fish poop, dead plant bits, etc.),

Iron is a key component for a substrate and pororsity and CEC.
I add a little peat and detritus from an old tank as well.
But many folks use soil, kitty litter and other richer substrates.

> we vacuum
> up on a regular basis (or, at least, it is common practice to do so).

Just the detritus that floats on the top of the gravel layer generally, few
vacuum the deep gravel ever.

> Second, our substrates are relatively porous and have many, many times
> the water flow rate of, for instance, a muddy swamp bottom.  I suspect
> this porosity and relatively high flow rate are what allow us to get away
> with water-column fertilization, as the nutrient-rich water is eventually
> circulated through the substrate, where the plants can take up the
> nutrients through their roots.

Yes, I think so but only up to a point.
You can see some of my older post on CPVC Reverse flow UG grids, heating
cables and no flow substrates. Yes, I got pretty good at water column
dosing. I got to a point where I had to take the next step which was
lowering the flow rates and noting the plant health growth reactions. I did
this for a few years. Iron certainly helps if nothing else. I found adding
flourite vs even the best RFUG the

I'd say 20-30% was the substrate and about 70-80% is water column for
relative importance with the wide variety of plants I was keeping at that
time(about 100+species).
Main notable improvement: much richer color, fuller growth, picky plants did
better, redder colors in many plants.
Better rooting. 
 
> For the discussion of substrates, I'm inclined to think that our tanks
> would benefit from some form of organic substrate, rather than rock.

Or slow release inorganic salts buried under 2-3 inches of sand flourite
etc. 

  The
> problem, I suspect, and why they aren't more common, is that organic
> substrates tend to make a mess in the water, and we tned to like and
> value clear water.  I'd appreciate any ideas for how to have an organic
> substrate without ending up with muddy water.  This Florabase may be
> interesting in that regard.  Would like to hear more about it.

Use agar nutrient media, add KNO3, peat, K2SO4, KH2PO4 and trace mix.
You could also add some rooting hormones and sucrose.
Depending on how much gelatin or agar you use, you can vary the consistency.
Thick tougher balls of this media rolled in peat and placed all along the
bottom of the substrate would slowly diffuse the nutrients out. The pore
size in the media will diffuse the nutrients at known rate.

If you used a richer organic media, the problem is that most of the N gets
converted to NH4+ or N2 gas.
NH4 + while being easy source of N, causes wonderful algae blooms(they
cannot resist a free lunch) if pulled up into the water column. Pulling up
plants/ re-suspension lake/river sediment dramatically reduces O2 levels as
most of these reduced forms are oxidized.
Small trace amounts being fed to the plants of NH4 from critter/bacterial
waste is fine and won't cause algae issues.

Soil tanks are great if you don't plan on uprooting the tank. But you will
want slower growth. I've had the same if not better result with flourite and
a bit more peat and detritus being added to a non CO2 type tank.

I think a flat cut to size piece of agar about 1 inch deep with the added
nutrients(no NH4) would likely improve growth in some species if added to
the bottom layer of sand/flourite etc.
You could even prepare the agar in the tank and fill enough in there to get
one inch and add the nutrients etc. Wait till it solidifies, add gravel on
top. For re dosing, add small ice cube sized pieces once every 3-12 months.

> Roger Miller may have had the best reply to this so far, under the topic
> of setting up a new 120 gal. tank.  I supposed I should be talking about
> fertile and infertile substrates, too.
> cheers,
> -david

Or infernal substrates:-)

I think the agar idea or a flourite mixed/rolled with agar/peat would do
well and not have too many problems.
I'd be interested to try this on a non CO2 plant tank. Hummm.......I do have
2x 4 gallon cubes sitting there and some agar.......

Question for the list: would you folks buy some if I made a batch?
 
Regards, 
Tom Barr

 
> [1]  I can't find a reference for this other than my class notes.
> 
> [2]  Chambers, P.A., et al.  1989.  "Roots versus shoots in nutrient
> uptake by aquatic macrophytes in flowing waters."  Can. J. Fish. Aquat.
> Sci.  46:435-439.  They found no significant correlation between water
> nutrient levels and biomass, shoot density or tissue nutrient
> concentrations.  Also, biomass and shoot density were consistently higher
> for plants in high-nutrient sediments than in low-nutrient sediments,
> regardless of water condition.  Finally, tissue nutrient concentrations
> were consistently higher for plants in high-nutrient sediments than in
> low-nutrient sediments, regardless of water condition.  Potamogeton
> crispus was used in this study.