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Re: Cyano Preliminary Results

> Given that Neil can identify our normal cyanophyte plagues as probably
> Oscillatoria or Lyngbya, can anyone produce a study indicating that
> Oscillatoria and/or Lyngbya are capable of fixing nitrogen?  
> I think our
> oft-repeated statement that low nitrogen levels or low N:P 
> ratios promote
> cyanophyte outbreaks is based partly on the factoid that some 
> cyanophytes
> can fix nitrogen.  I'd like to see more specific information.

Nitrogen fixation is sensitive toward oxygen, so much that it can be
considered as a strictly anaerobic process.  However, some blue-green
algae have developed a special cell called a heterocyst, which is
nonphotosynthetic, does not produce oxygen, and has a thick cell wall
which prevents oxygen from diffusing in.  These blue-greens can fix
nitrogen in an aerobic environment, and will form more heterocysts in a
low-nitrogen environment

There are three basic kinds of nitrogen-fixing blue-green algae:  1)
filamentous heterocystous species, 2) some unicellular, nonheterocystous
species, and 3) some filamentous, nonheterocystous species.  The
nonheterocystous species can only fix nitrogen under hypoxic conditions,
so I think we can assume these species do not fix nitrogen in our
aquaria, at least not in the water column.

That leaves us with the heterocyst-bearing species as potential
nitrogen-fixers in our aquaria.  Oscillatoria and Lynbya do not possess
heterocysts.  However, Anabaena sp., which is a common component of
blooms, does possess heterocysts.