Re: Aquatic Plants Digest V2 #225

> From: jphealy at sysconn_com
> Date: Sat, 28 Sep 1996 09:10:56 -0400 (EDT)
> Subject: airstone anathema
> >To suggest that airstones are somehow 'bad' for aquatic plants is wrong,=20
> >wrong, wrong (to repeat a recent post)! There is clear research which=20
> >indicates that photosynthetic rates in aquatic plants increase with=20
> >increased rates of aeration ... the reason is that increased aeration=20
> >increases water movement and therefore decreases the thickness of the=20
> >boundary layer
> This is interesting. My impression has always been that the purpose of CO2
> injection is to increase the water's content of CO2 to a level higher than
> equilibrium with the atmosphere. If that is the purpose, then aeration would
> defeat the CO2 injection. Or at least decrease its effect. 

Of course aration will decrease the effectiveness of CO2 injection. That 
doesnt make aeration bad for plants however. My point was that CO2 
injection is unnecessary under most conditions and that the same effect 
could be achieved through adequate water movement in the tank. Why? 
because limitation of growth by CO2 is not due to the inability of plants 
to fix CO2 but rather due to the high diffusive resistance of CO2 in 
water. To increase the rate of diffusion you can increase the gradient 
(CO2 injection) OR decrease the path length (water movement, aeration 
etc) ... which is easier? CO2 injection is only necessary when you are 
growing plants which are completely unable to utilize bicarbonate AND are 
exposed to elevated CO2 in their natural habitats ... such as matt 
forming species which trap CO2 that has been release from the sediment.

The whole hearted endorsement of CO2 injection is part of what I call the 
'sick and dying plant' syndrome ... people have this opinion that aquatic 
plants are delicate and hard to grow and so treat them like a dying 
patient hooked up to life support. In reality, however, most aquatic 
plants are agressive, noxious weeds and will readily take over your tank 
given even half a chance. For example, a few years ago I was charged with 
the task of growing large quantities of healthy Lemna trisulca (the 
submerged duckweed). The experts said it was very difficult and that you 
needed a sugar supplement and a full complement of vitamins and very low 
light (otherwise the plants would die) and an acidic pH etc etc. Yes, I 
grew Lemna trisulca under these condition but it was difficult and 
incredibly time consuming. Then I thought, this is crazy, and I removed 
the sugar, removed the vitamins, increased the light to about 20% full 
sunlight and incresed the pH to 8.0. The growth rate more than DOUBLED! 
the plants were healthy, and I spent my time doing other things rather than 
carefully nursing 'sick and dying plants'.