Re: Allelochemicals, roots and competition
> From: Charley Bay <charleyb at hpgrla_gr.hp.com>
> [snip] While some plants do grow
> better in the presence of other plants of the same or different
> species (usually a result of micro-climate modification), any plant
> "aware" of another plant is fundamentally in direct competition
> with its neighbor. From studies on terrestrial plants, the "first
> day" after pruning is absolutely the most productive day for
> growth (given a constant nutrient sufficient environment).
Could you explain this more? Why is the "first day" important?
I guess I'm interested in the mechanisms of competition.
We are probably familiar with the competition for light and
to a degree, nutrients...
How does it work for plants with an affinity? Do we know of
aquatic plants like this?
> The NPP can stagnate at zero for decades for many trees
This describes the behaviour of the Madagascar Lace plants currently
in my large tank very closely. No obvious algae attacks, no brown
spots, small but apparently green healthy leaves, nutrients in
solution and supplement tabs in the substrate yet no growth.
This shift into a dormant phase happened too rapidly (I think) for
it to be accounted for by the seasonal dormancy theory or by
a decrease in temperature. The darn things should have gone through
a phase of moderated growth with emphasis on building reserves in
the tubercle. Its just as if everything else was growing so well
so it didn't.
> I'm convinced that many of my plants that
> have heavy competition on 4 out of 4 sides have an NPP of zero, but
> seem to exist fine for a while until I get around to pruning
> everything back (this is more easily demonstrated for rosette-type
> plants than for stem plants that merely extend upwards.).
You are pruning the leaves not the roots right? Assuming that the
primary competition mechanism here is for light. Yet A. mad. will
continue to show very slow growth even with trimming back the
neighbours. Some even suggested that Crypts and this Aponogeton
had an affinity; increased oxygenation due to the roots of the
> One more thought on competition: for many terrestrial systems, the
> actual competition is almost *entirely* below soil. Many fields
> don't have trees simply because the competition for root space is
> so complete that nothing can get a foothold (even though the
> established plant species does not appear to exude allelochemicals).
> In these fields, trees simply cannot grow because root competition
> is so severe, even though sufficient light and water may be
> available. I am absolutely convinced that this also takes place
> in aquaria around mature species with strongly developed root
Yes! What is the primary mechanism here do you think? Are you
suggesting that we might consider root pruning? I think George
advocates pulling up plants regularly during pruning. Do you
> That, I suppose, is the art; are we gardener (the population) or
> horticulturist (the individual)? Some of both, I should think.
For the Madagascar Lace plant we've got to focus on that individual
since its demands seem so exact and unfortunately, unknown. I'd
give a lot to know how those guys in the Philippines are growing
these things, if its true that they are being cultured there now.
Is anyone in touch with some aquatic researchers who knows someone
who is studying these Aponogetons?
John Madesen wrote:
> I am replying to the comment about rooted plants outcompeting algae
> for nutrients. Scientifically, there is no good basis for this statement
> if you mean nutrients in the water. Research has shown that rooted
> plants take most of their required nitrogen and phosphorus from the
> sediment, not the water.
This is very fascinating indeed. Perhaps all of our supplementation
should be done within the substrate. It also corroborates the
theory that iron-oxide in laterite is useful for fixing phosphates
in the substrate. It makes me wonder more about the value of a
slow RUGF system with an iron-oxide, high CEC substrate. Maybe
it is a case of serendipity that a particular tropical or subtropical
location may support this Aponogeton and one should take soil
samples and observations there to attempt to duplicate this.