Re: Aquatic Plants Digest V1 #154

>Aquatic Plants Digest    Wednesday, 27 December 1995    Volume 01 : Number 154
>In this issue:
>        "string of pearl" bubbles really O2?
>        Re: Planted Rift Valley Tanks
>See the end of the digest for information on subscribing to the
>Aquatic Plants mailing list and on how to retrieve back issues.
>From: Jim Kostich <jkost at ix_netcom.com>
>Date: Tue, 26 Dec 1995 17:21:25 -0800
>Subject: "string of pearl" bubbles really O2?
>Just out of curiosity, has anybody ever really checked to see if the bubbles
>rising from underwater plants are really O2 - or just CO2?  A couple of
>things make me wonder if it might be the latter:
>1. I've never noticed these bubbles in a plant tank without CO2 injection -
>no matter how intense the light.
>2. The way streams of bubbles seem to be emitted from a single point on a
>leaf sure seems unlikely.
>3.  It just plain LOOKS like the bubbles that rise from the bottom of a
>glass of seltzer water!
>Hey, Jim, How is it going?

Plants do really produce O2 when photosynthesizing, but the bubbles given
off are not 100% O2 because there is time for exchange with dissolved
gasses in the water.  N2, dissolved in the water diffuses into the bubbles,
and some of the O2 in the bubbles diffuses out into the water.  Aquatic
plants have an interconnected system of air spaces that runs through the
leaves, stems and roots.  When photosynthesizing actively, the O2 produced
is added to the air spaces, and the pressure goes up until the gas starts
escaping from some break in a leaf, stem, or root.  These breaks are
natural, and should not be considered an injury.  Probably the content of
O2 is a lot lower than 100% even before the gas escapes because of
diffusion of N2 in and O2 out through the leaves, stems, and roots.  I have
seen aquatic plants produce streams of bubbles when in sunlight, even
though I have not added any CO2.

Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174