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Re: Allelochemicals, roots and competition

> > From studies on terrestrial plants, the "first
> > day" after pruning is absolutely the most productive day for
> > growth (given a constant nutrient sufficient environment).
> 
>Stephen.Pushak at saudan_HAC.COM responded:
> Could you explain this more? Why is the "first day" important?

I'm using "first day" as a metaphor for the first productive period
of growth after trimming/pruning/thinning of the individual/stand/
population.  Depending on the (usually environmental) circumstances 
around the thinning procedure (and to some extent the parts of the
individuals removed, some structures being more critical to 
developmental survivial than others), some vegetation may go 
through some form of shock.  After this recovery, the plant is 
*best* able to grow at that one point in time than ever again.  
Foresters term this "release".  

Assuming a steady-state environment, the plant after pruning will
have *maximum* access to nutrients, space, and light with the
lowest competition.  Young vegetation *always* grows better than 
old, and no plants ever get younger.  The longer the plant waits 
for release, the more difficult the individual has in adapting 
(reacting) to favorable release conditions.

Also, many plants seem to be morphologically ready to "seize the 
day" at the first disturbance that lends one individual the upper 
hand (and thus out-compete its neighbor, if it can just get a 
*little* taller than the neighbor, or get those roots a *little* 
deeper than the neighbor).  Often, the first individual with the 
upper-hand can keep that upper hand *forever*.  This is the case 
in the Pacific Northwest, USA.  If you cut down forty acres up 
there, will it be succeeded by a bunch of Abies lasiocarpa
or Pseudotsuga menziseii?  Both species are present;  however, the
next generation will be *entirely* dependant on which germinates
first.  Once one gets the upper hand, it wins for a century.  The
other species is present, but in a sickly, over-shadowed, barely
competitive existence.  Perhaps the next generation (after the next
fire) it will win.

Sometimes, the first individual has the upper hand only until
genetic limitations come into play.  In California, USA, a fir can 
have the upper hand over a redwood seedling for several decades.
If the redwood can merely keep up (even though it has *less* access
to light, water and nutrients), it *might* be able to over-top
the fir simply because morphological limitations of the fir species
halt the fir's ability to get taller.  The redwood may never
"break through" the canopy, but if it does, it becomes the dominant
kid on the block because it is genetically capable of getting 
hundreds of feet taller.  Sometimes, this is merely a matter of
time:  redwoods live longer than fir, so an aged fir forest is
often succeeded by a young redwood forest.

Getting back to the "first day", some individuals *can* release, 
while others (if they exist at a very low NPP for a significant 
portion of their lives) will never release even though an 
infinite amount of space, light, water, and nutrients are 
available.  This is because vegetative individuals usually are able 
to adapt a "maintenance" existence or a "capitalist" existence 
depending on environmental inputs during critical formative periods
in the plant's developmental life.  If anybody is interested, I
can explain why the 60-year-old 1" diameter Pinus contorta *cannot*
release, but the 90-year-old 12" tall Picea engelmannii *can*
release (from my previous post).  Both are environmentally 
determined, not genetically.

Some plant species are successful entirely because this approch 
is genetic, not environmental:  many species of woody and herbaceous 
plants perform *all* of next year's mitosis (cell division) growth 
in the late portions of the previous growing season.  These divided 
cells simply do not "expand" (you don't see the branches getting
longer) until next year.  Thus, if next year is a drought year 
(for terrestrial plants) or nutrients are in very 
short supply, the cells will expand minimally (or even not at all).  
The plant is only marginally (or not at all) stressed because it 
can even "skip" or minimize the mitosis for the following year.

If it is a great year, the cells can "expand" to their fullest
potential, and perform a larger amount mitosis for the following 
year.  Thus, these plants are termed "conservative", and are not
able to capitalize on good years (but are not damned by bad years).
However, most plants are "capitalists", and perform the current 
year's mitosis and cell expansion completely dependant on the current
year's nutrient availability.  They can best take advantage of
(capitalize on) nutrient availability, but can be very stressed if 
a "false start" on nutrient supply for the year falls short of the 
plant's later needs for completion of the cell expansion process.
For example, a "false growing season" that forces many plants to
"break bud" and expose the sensitive terminal meristem (where the
growth takes place) may be followed by a killing frost.  The 
capitalist can loose all of its meristems (all its growth for 
that year), but the conservative plant is merely temporarily 
halted (no damage, full recovery when the "real" growing season 
starts).

> How does it work for plants with an affinity? Do we know of
> aquatic plants like this?

Hmmm... Affinity?  You mean some plants doing better in the
company of others?

For terrestrial plants, the term "micro-climate modification"
refers to a localized change to the environment.  Often
this change can create an environment favorable (or not favorable)
to new species.  For example, the genus Pinus (the pines) usually 
like arid, open mineral soil for germination.  This is
because CO2 from decomposition in a heavily organic soil inhibits
the germination process.  Pine typically can't get a foothold
in sites where trees are already growing.  Thus, "micro-climate
modification" by mosts trees inhibit the development of pine.

However, moisture is usually the limiting factor in vegetative
development in arid areas.  Trees (or other vegetation) can take 
root in the shade of other trees, simply because a marginally 
higher humidity (from nearby evapo-transpiration from mature 
species) and lower solar demands on the plant (from shade) may 
allow a different species to be successful under the canopy.  This
is very true in many of the tropical forests:  Take out the top
canopy, and watch the species densities change below the canopy.  
Some species may go away completely, because they are unable 
(morphologically) to handle the different conditions. The best 
demonstration of this is "eco-types" which picked up a lot of steam 
in the past decade or so.  As it turns out, some species tend to 
be very successful in the presence of other species.  The principle
of "eco-types" is that given a number of species found on the site,
we should be able to predict the other species we *will* find on
the site because (1) the site is conducive to their growth, or (2)
these species are found together often enough that we speculate
some causal relationship.  Further, ecotypes are being used to
abstract additional meta-information;  the USDA USFS eco-type
"PICO-ARUV" refers to "Pinus contorta" in the over-story with
"Arctostaphyllus uva-ursi" in the under-story.  Because they have
studied enough "PICO-ARUV" sites, they can generalize as to
slope, water drainage, nutrient availability, clay content,  
solar exposure, elevation, and a bunch of other factors for that
site.  If anyone is interested, we can take specific eco-types 
off-line and speculate as to the causal relationship.

For the aquaria, we probably don't have our tanks up long enough to
witness an eco-typical shift over the maturation of the system
(or the tank may not be large enough or not have the species 
diversity adequate to allow a "natural" or otherwise competitive 
shift to take place).  However, we can mimic our understanding 
of eco-types by placing low-light plants under high-light plants, 
where the low-light plants may otherwise be forced to "grow too 
quickly" by the high light. (Most plants are like candles:  You 
can burn them fast or slow, but you only have so much to burn;  the 
longest-living plants in the world exist in the harshest climates 
(lichens, bristlecone pine, aspen) where the growing season may 
only be a few days a year).  There may be other interactions
between specific aquatic plant species that I am not aware of
that may increase the survival of both. (For terrestrial plants,
many individuals of the same or similar species actually "fuse"
root systems and share nutrients in times of short supply;  also,
many symbiotic relationships exist, such as mychoriyzae fungus
aiding the water uptake to plant roots, or nitrosommonas bacteria
fixing nitrogen in the root nodules of legumes, or mistletoe
actually living in the vascular system of higher-order plants, or
bromeliads relying upon shade, protection, and support [canopy
positioning] from other plants).

Of course, as you already mentioned, it appears that a 
well-developed root system in the aquarium substrate aids all 
plants in the aquarium by ensuring that enough water uptake
forces good oxygenated circulation through the substrate (at a
very slow rate, of course).  This is an excellent example of
micro-climate modification in the aquarium where one species will
benefit another (I would *not* call that symbiotic or mutualism,
though).

> You are pruning the leaves not the roots right?
> Are you suggesting that we might consider root pruning? 

I mostly prune leaves;  However, (IMHO), I think root pruning (or
splitting plants by the roots) is absolutely necessary in an aged 
tank; I do that as I find mature root systems in my tanks.

Sorry, I did it again.  A long post.  I'll shut up now.  :^>


--charley                           Fort Collins, Colorado USA
charleyb at gr_hp.com	or	charley at agrostis_nrel.colostate.edu