r norman  wrote in
news:c6fg11$246c$1{at}darwin.ediacara.org: 

> On Sat, 24 Apr 2004 04:46:39 +0000 (UTC), Tim Tyler 
> wrote:

>>Because of global competion for nutrients, organisms do not have
>>to be in the same environment or physical location to be in
>>competition with one another.
>>
>>I.e. those resources that are tied up in the form of forests should be
>>subtracted from the pool of resorces available for forming bacteria.
>>
>>It is true that - at the moment - complex life is doing rather better
>>on land than in the sea.  However, that situation is probaly not going
>>to last for very long.  We can expect some serious reinvasions of the
>>ocean as the land continues to fill up with complex organisms.
 
> You persist in these strange ideas.  Probably the most critical
> nutrient (in the sense that it is usually a limiting factor in growth)
> is nitrogen and the only source for usable nitrogen by complex
> multicellular organisms is nitrogen fixation by bacteria.  All other
> limiting nutrients like phosphorus or iron or whatever other trace
> mineral are usable only when dissolved in water and then the bacteria
> really do get first crack at them.  Only in a tropical rain forest do
> you find nutrients primarily tied up in multicellular organisms and
> there they are almost entirely in plants, certainly not animals.
> Again may I remind you that this habitat, impressive as it is, forms
> only a tiny fraction of the biotic world.

Actually the total contribution of nitrogen to the nutrient cycle from
anthropogenic sources (fertilizer production, fossil fuel combustion,
and  legume cultivation) is currently approximately equal to the amount
of natural fixation. Unlike carbon dioxide, the potential impacts of
this has received little attention in the popular press. The impact of
anthropogenic phosphate production (also significant in comparison to
natural phosphorus cycles) is probably better recognized by the public,
although phosphate is generally the limiting nutrient only in fresh
water environments. I would also note that, in those environments,
rooted aquatic plants and floating macrophytes such as duckweed
frequently outcompete cyanobacteria and unicellular algae for the
available phosphorus. 


Now as to the thrust of Tim's argument that we will soon replace the
nutrient cycling function of bacteria, I am somewhat dubious - but
partly because I think it will prove cheaper to utilize existing natural
cycles than to try to take over all these functions with technology.
This argument reminds me of the dichotomy between Planet Managers and
Planet Fetishers described by Evan Eisenberg in "The Ecology of Eden".
Either technology will save us or the return to nature will triumph.
Eisenberg thinks we need to find a middle way, and I tend to agree with
him. 


Yours,

Bill Morse
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