[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
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.
Regards,
Mark