[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: BGA and nitrogen fixing...

Chuck Gadd wrote:

> I know someone on the list (Tom?) recently posted results of a study of BGA,
> and found that the samples he examined didn't have the necessary parts to
> be able to fix nitrogen from air.

Tom provided us with some nice observations.  He confirmed something
that came up on the list 2 or 3 years ago in a conversation with Mark
Fisher and Neil Frank.  It may have been known before that.
> I occasionally get a little BGA in my main tank, whenever I get lazy, and
> don't prune the plants when I need to.  In those cases, where the tall stem
> plants reach the surface, some of the leaves right at the air/water boundry
> get covered by a coat of BGA.

I've seen that happen, and I've also seen little colonies of BGA
inhabiting the growing tip of some stem plants, well below the water
line.  No other BGA evident in the tank.
> Prior to reading about the microscope examination of BGA, I assumed that the BGA
> was thriving there due to being able to extract nitrogen from the air.  No
> traces of BGA anywhere else in the tank, except a little in the tubes of my
> overflow box.

The BGA certainly wouldn't need to grow at the water surface to reach
nitrogen.  Atmospheric nitrogen dissolves in water to a concentration of
about 15 mg/l, so it would always be available to a nitrogen fixer in
reasonable amounts.

> Can anyone offer any possible explaination for this pattern of BGA growth
> other than nitrogen fixing?

Probably the bga profits from the brighter light at the surface.  Also,
the bga may be able to get CO2 from the air more readily than from the
water because of the thinner boundary-layer effect.

Finally, I think it was Peterson and San-Jensen that observed that water
transported through aquatic plants was eliminated mostly through the
growing shoots.  The water would probably carry with it nutrients
concentrated by the plants but available in excess of the plant's needs
and possibly it would carry organic compounds synthesized in the plant
and transported in it's vascular system.  Those nutrients and organic
molecules could promote growth of bga.  If true then that would also
explain the little colonies of bga that I see growing on the tips of
stem plants.

Roger Miller