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- To: <Aquatic-Plants at actwin_com>
- Subject: Re: Woots
- From: Thomas Barr <tcbiii at earthlink_net>
- Date: Fri, 05 Jul 2002 02:01:17 -0700
- In-reply-to: <200204022048.g32Km1203899 at acme_actwin.com>
- User-agent: Microsoft-Outlook-Express-Macintosh-Edition/5.02.2022
> I think the trick here is to place the 'missing' ingredient(s) in the
> substrate. Since I have a relatively high fish load, I end up with a lot of
> N and P in the water column. Makes no sense to dose those two into the water
> column at all.
Well, fish add NH4 and any that gets to the bacteria and turned into
NO3(ideally none), unlike KNO3. NO3 limitation/high levels were the other
"issues" for algae.
Big difference in these two N species and NH4 is a big algae contributor at
least that's what I find/found.
> Wouldn't keeping N and P out of the substrate make the plants
> pull them from the water column?
Yes. A little but not much in the substrate is fine, roots need these as
If you gauge the rate of root respiration per ion absorbed or per unit of
root biomass produced, at low limiting NO3 these rates are quite high.
This suggest there is a specific cost for maintaining/producing/absorbing
these nutrients when times are lean.
But shoot respiration is not as pronounced nor as consistent when NO3 is
Root respiration accounts for about 10-50% of the total photsynthate
produced. This percentage is much higher in slow growing species.
> But what about K and Fe (and the associated
> micros)? If the rooted plants are pulling N and P out of the water column,
> why not place K and Fe in the substrate in order to facilitate the plants
> and starve the algae?
I don't think you are going to bind K+ to much, like NO3(these tend to
disassociate completely in solution, like Na and Cl). Fe yes, but it doesn't
take much Fe to make algae happy and able to grow, parts per Billion. Iron
limitation in algal studies is tricky since it is at such low levels.
Low iron technique is required simply to do these studies on iron
limitation of many algae. This took many years to develop before some great
work was done in this area. Plants will use far more iron and will be
limited before algae will be.
For us, this(the plants) is the only practical method of assessing iron from
a biotic standpoint IMO. Uptake is complicated by various issues, a good
look at the plant itself is a good gauge.
Other traces? Perhaps an imbalance may favor the algae but I doubt this.
Algae simply are too small and efficient to beat in this manner. If algae
only need 1 unit of food(nutrient) to live for one day and a plant needs
20units, well who's going to starve? Plants can and will go dormant in lean
times. Not much O2 is produced, photosynthesis declines etc. Algae might not
be able to grow as massive but some will always be waiting and doing okay.
> Isn't that the basic premise, are far as Fe goes, of
> both laterite and Fluorite?
Iron's a funny nutrient in the water. I might not ever know all the
mysteries surrounding iron. One could devote their entire career(some indeed
have) to just that. Laterite and iron bind PO4 into the substrate to be
extracted via the roots. That's the whole idea anyway. One can find this in
nature as well. But simply because it exist in nature does not imply this is
what is causing good plant growth/algae growth etc or that roots allow algae
not to exist where plants are simply because the plants can extract the iron
via the roots. There may have been enough Fe for algae to grow there but
something else is causing their demise/reduction/absense.
There are other things in the substrate besides Fe, K, PO4 etc. There is a
biotic element that is dynamic. Roots actively change the substrate as they
move through it. So do the associated bacteria/fungus.
Break it down into the biological(by the plants, bacteria etc),
mechanical(heat, grain sizes, internal pore sizes in the grains, consistency
of grain sizes etc) and the chemical elements, not just the chemical.
Sometimes you cannot reduce it down to a simple thing. Much of it is
interwoven. A story within a story that relates to yet another story.
Understanding one story and how effects the rest of the story, one at time
can help to get a feel for what is causing what.
PO4 causes algae was one such example. Everything else had to be "right"
before I/we could say that high PO4 levels(say 1.0-1.8 ppm) doesn't cause
algae when we have good CO2, low NO3 , etc.
How much effect does each method/nutrient give you in relation to what you
want(less algae better plant growth in this case)? I think that is a key
question. That can be a long process. I think we've come a long way with a
lot of discussion of the macro nutrients.
The traces will be more difficult for us to control and assess
experimentally. But I think we can deal with it since they are traces, we
don't expect them to have a large impact on the plants unless they are too
low/limiting plant growth.
A word about comparative differences: many plants have quite different
abilities, uptake rates of each type of nutrient, different growth rates
etc. Generalizing can get you into trouble here. Be careful when assuming a
crypt and Egeria do the same thing.
I hear a lot of talk of limiting algae, but little of limiting plant growth.
Plants have a much more testable range than algae for studying limitation of
nutrients. Making them happy, makes the algae unhappy and don't forget your
Take a good look at them when you hack and prune your tank, not just the
above ground parts.