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Re: PO4

>  However, phosphate
> would seem to be a resource that can't be partitioned.  All plant species
> need it, and, unless the plant is parasitic, it is going to have to get it
> from the same source.  Thus, it follows that the competition for phosphorus
> is severe, and that all the tricks possible for improving uptake would have
> to be possessed by most or all of the competing species.

How about r vs K strategies? The paradox that one finds in the water column
regarding _algae_ competition is that the smaller the algae, the better they
are at K strategy. The bigger phytoplankton are growth specialist rather
than K specialist which is not what one would expect based on what you would
gather from terrestrial systems.

Perhaps the same can said for plants. The "trick" is to keep their nutrients
up (assume they are indeed r strategist) without letting the nutrients dip
too low where they are stunted for any reason.

r startegist will grow like crazy when there are nutrients available(say
diatoms vs prochlorococcus-a picophytoplankton) and produce a resting stage
until there's enough nutrients and light available again. Plants do the same
thing in the spring and summer and then seed(the resting stage) in the fall
to make it through rough times.

Another ecology notion is recruitment probability. Assuming that algae and
plants have the same competitive abilities, who gets there first will have
the best chance at being dominant. Adding/having a ton of plants from the
start applies to this idea. I doubt that plants and algae have the same
competitive abilities but in some respects they do when it comes to uptake
of resources. 
> Thus, if you can detect any phosphorus in your tank water at all, the
> plants are probably well supplied and their tissue contents are likely to
> be well above the critical value.  If the phosphorus content of the water
> drops after you add phosphate, it could be due to the plants increasing
> their luxury consumption.  It does not mean that the plants were actually
> deficient. 

Very true. But keeping them well fed doesn't seem like a bad idea either.
It also seems that anytime there's a stress to the plant that they do not
need to spend any extra energy when times are leaner for uptake of this
particular nutrient.....this might allocate more energy to other nutrients
that they need more at that time allowing better growth on nutrients that
cannot be stored as luxury nutrients.

> Also, there may be other ways that phosphorus is removed from
> the water column, such as reacting with iron or calcium and precipitating
> out.

I considered this. Can I assumed that after a long period of extensive
additions of PO4 that the gravel, substrate will be fully saturated with
FePO4? Seems reasonable. Lots and lots of PO4 and very little iron.

Ca ? Not sure about that one. Could be but the plants do grow like mad after
adding the KH2PO4.

Rooted vs non rooted plants also show the same dramatic growth when PO4 is
added(Riccia etc).

Primary production rates are increased when PO4 is added above these "non
deficient" levels(say .2ppm or less of PO4) also (at least with a number of
plants). While measurement of O2 leaves something to be desired as does PP
rates in general one can see this with Riccia and a number of other plants
by simply adding KH2PO4 to a tank with low(say .1 to .2ppm of PO4) PO4.
Raise it up to .5ppm or higher.
I do not know where the amount added slopes off and adding any more will not
help. I'd say about 1.0ppm or so If I where to guess. Not sure. Ca may be a
cause, I'll look into that potential. Iron I can rule out. The PO4 gets
removed too fast for the substrate to be a component.
That's all for today:-)
Tom Barr  

> Paul Krombholz, in warming central Mississippi, expecting a nice day
> tomorrow.  
> ------------------------------