Re: Aquatic Plants Digest V1 #297

> From: nfrank at nando_net (Neil Frank)
> Date: Sat, 2 Mar 96 06:19:37 EST
> Subject: Re: CO2 and aquatic plants
> >From: Elizabeth Worobel <eworobe at cc_UManitoba.CA>
> >Date: Fri, 1 Mar 1996 15:00:47 -0600 (CST)
> >Subject: Re: CO2 and aquatic plants
> >
> >Hey Steve, not to get too picky, but there are very few aquatic plants 
> >which obtain CO2 from the sediment. These are Isoetes spp., Littorella 
> >uniflora, Lobelia dortmanna, Eriocaulon spp. Generally, this ability is 
> >restricted to small rosette plants growing in extremely oligotrophic 
> >waters. Other species, such as Valisneria spp., Heteranthera dubia 
> >and Myriophyllum spp. have been tested and found not to have the ability 
> >to extract CO2 from the sediment (Hydrobiologia 98:3 - 7, 1983).
> >
> Not to get too picky, but how do you know that the above plants are THE only
> plants?  Have all tropical species been tested, including Echinodorus,
> Cryptocoryne, etc?  Also, can't the sediment (or the substrates used in
> aquaria) be a source of CO2?
> Dr. 'Flammenwerfer' Frank :-)

Well Neil, you got me there. My post was certainly a sloppy bit of 
writing. Can I blame it on the weather ... last night it went down to 
-30C with a 2100 windchill!? What I was trying to say was that evidence 
suggests that the ability of aquatic plants to extract CO2 from the 
sediment via the roots is a specialized response  to extreme 
environmental conditions. So far all plants which exhibit this ability 
are rosette plants with very large root systems ... up to 70% or more of 
total biomass. They are uniformly found in aquatic environments with a 
severe shortage of CO2, either because the waters are oligotrophic 
acidic softwater or because of complete depletion of CO2 in the water 
during the day. This is not an ability which would be expected to be 
found generally, but of course not all species have been tested. The few 
species that have been examined which dont 'fit the profile' so to speak 
 were all unable to extract CO2 from the sediment.
Actually, the ability of these rosette plants to extract CO2 from the 
sediment is not the most fascinating thing about them (IMHO) ... what I 
find really neat is that most of them have the ability to fix CO2 at 
night in the dark! They do this by attaching the CO2 to organic acids and 
then reducing the CO2 in the following light period when energy produced 
from light becomes available.
As to your second point, physiologists have long suggested that low mat 
forming species make use of CO2 diffusing out of the sediment. The moss 
Fontinalis, for instance, requires very high free CO2 concentrations when 
grown in the lab. This suggests strongly that they are making use of 
sedimentary CO2 in a natural environment.

Finally, are you going to banish me to the wasteland of sci.aquaria if I 
continue to sign as Dr. dave? There I can talk to myself to my hearts 

Dr. dave