Re: alleopathy

[Thomas Barr <tcbiii at earthlink_net>]

> If I may so bold as to quote her without permission (Chapter 3, page 51) [I
> take full credit for typos]:
> - -------------------
> Q: Do you see any advantage in setting up a High-tech' aquarium?
> 
> A:  Yes and it is because alleopathy is reduced in these tanks. Generally,
> high-tech systems advocate frequent water changes. Also, many tanks have
> substrate heating cables, which induce water circulation into and out of the
> substrate. In essence, the substrate is continuously 'washed' so that the
> alleochemicals are brought into the overlying water where they can either be
> metabolized or diluted out.
> Thus, alleochemicals are prevented from accumulating in both the water and
> substrate in high-tech systems. Auto-inhibition is lessened and stroingly
> alleaopatheic plants are prevented from dominating other species..
> Generally, a much wider variety of plant species can thrive within the tank.
> Thus, hobbyists with 'High-tech' aquaria can indulge in aquascaping and
> carefully controled plantng schemes.

This same argument was addressed in the Optimum Aquarium book.
Please do tell me of a strongly alleopathic submersed aquatic plant. I don't
know of any and I'd bet a nickel you'd have an _extremely difficult_ time
finding anything even remotely worthy of a generalization regarding this.

Most secondary plant compounds are for plant defenses and antiherbivory.
These are the chemicals most often alleopathic in nature.

This effect has been documented having an impact in terrestrial systems but
not aquatic systems. Competition between plants(and algae) in aquatic
systems is mainly a matter of light, not chemical warfare.

In aquatic systems:

The alleopathic test I've seen often involve grinding up some plant, using
the extract or extracting the terpinoid, phenol etc and adding this to an
algae culture. Sometimes the algae culture protocol is questionable. Similar
problems exist in plant-plant effects.
Not every realistic to the planted tank nor natural system.

Grinding something up is not the same as plant living and existing in
nature. But at the levels and concentrations they also apply these chemical
compounds are not realistic to most of the aquatic ecosystems. 1: 5 200
grams of plant material in 200mls of water diluted 1:5 is not natural nor
would I argue it would be. This is extremely concentrated, and very fresh,
many of these compounds are broken down and removed from the system.

When plant cells are damaged/lysed, many of the chemicals stored within the
membranes are leaked out into the system that normally would never leak out
much naturally.    

How would a plant know how big the body of water they live in is?

Take a look at natural systems involving two typical aquatic systems.

Many plants live in lotic (moving waters) systems. The loss of these
compounds would be only unidirectional(downstream) and too rapid to have any
effect in surrounding regions. These compounds would no effect upstream.
In lakes(lethic systems) the question would be how does the plant know how
big the lake is, will it dry up in a few months or freeze or how much
turbulence/wave action/outflow etc the plant lives in.

I find the same plant diversity in lakes as I do rivers(at least here where
there are lots of lakes(about 8000 and streams with aquatic plants). There
are also road side ditches which would make great places to study such
interaction(small with lots of species, little outflow, lots of sampling
sites, easy to get to, etc)

The reasonable place the allelopathy might occur is in the substrate.
Concentrations can have the time to build up without wasting it out into an
unknown environment, the water column. Many substrates have very little
in/outflow. 

These would be the best candidates but nothing has been shown I'm aware of
in this type of situation. This would only effect plant-plant roots and
mainly competition for nutrients. There's no need for water competition.

A better strategy would be to put the plant's resources into the leaf
production/stem elongation and beat the other plant out by light
competition. Or else grow slow and not need much light etc. There are other
methods but alleopathy is pretty far down the list.

Dry ecosystems/deserts seem better suited for alleopathy where these
chemicals can build up/less diluted and plants can "defend" a root zone and
have more access to water/limiting resources.
 
 But considering the flow rates in our tanks, much of this will leak out
into a oxidizing environment FROM a semi reducing substrate
environment(generally). Those chemical compounds may act quite different or
not at all when they go from one redox state to another. Many are volatile
and decompose rapidly.

But considering the flow rates with most folks tank's substrate with it's
large grain sizes, will anything build up? Not likely.
What happens when you do a 50% weekly water change? Do the chemicals stay in
the gravel? What happens when you replant and uproot things?

Production of many of these compounds is often very sluggish (which can also
make it it difficult to study). Although some may have highly effective
responses to other plants/algae etc, the low concentrations when removed to
the water column reduces even these potent compounds a great deal(several
orders of magnitude).

I would believe variations in nutrients would be a larger driving factor for
declines in non water changed tanks. Another would be nutrient needs and
other habitat signals that are not involved in alleopathy, such as build up
of NO3, very soft water, acidification. Some plants need more Cu or P than
others. Adding everything for all the plant's needs is rather tough through
dosing only. Few have been able to do this with CO2 injection and testing is
of questionable use depending on what types of kits were used. You can guess
to some extent, but balancing the levels over 3-6 months is going to be very
tough and wrought with problems.

Water changes make this range much easier to achieve(seems more likely the
issue-plant's nutrient needs for optimum health) and if alleopathy exist to
a significant level in our tanks, then this would remove it as a player in
the planted tank. But how much? Which plants? Would there be enough
production of these allelopathic chemicals in one week or 3 months to cause
any significant impact?

Adding activated carbon would remove these.
Carbon was added to absorb these chemicals to roots of terrestrial plants
and restored normal growth.

DW and folks that often talk of the allelopathy are speculating and indeed
she says so and says they are "mildly" inhibitory. I think it's about all
that's been shown thus far. Even the scientist that study allelopathic
chemicals have a great deal of trouble addressing plant plant interactions
or algae plant interaction in natural systems. I've seen numerous thesis on
this topic. 

Humics seem a good bet for reduction of certain nuisance algae. I cannot get
some species of algae to grow in some humic waters. GW for example. DW makes
a case for these as have others for influencing plants and algae. Odd
diatoms, lowing of light intensity and very acid waters are often the
results of tannins and humics.

But tannins and humics stay at relatively stable constant concentration
levels so the input is = to output here in Florida. Therefore some
substantial decomposition does take place.

She speculates and if taken piece meal one can draw different opinions, but
if you take the book as a whole, I think it's pretty darn good.

So if cables are good at getting rid of alleopathic build up what about RFUG
filters? They should be as good if not better at achieving this?
Maybe that's "too much" of a good thing and needs to be within a range?
That's a shaky argument for using cables/RFUG/nothing at all.

Regards, 
Tom Barr