# Krause's Hypothesis - Is Oxygen Bad for Plants??



## MiamiAG (Jan 13, 2004)

In 1988, Hans J Krause stepped up to the International Congress in Aquaristics in Monaco and pronounced that oxygen was harmful to aquatic plants. This assertion was published in a series of articles and, later, in a self-published book. It has sparked many years of debate.

An article published in Aquarium Heute summarized Krause's observations as follows:


> H.-J.Krause observed improved plant growth in aquariums with a lower oxygen concentration, compared to aquariums with a high concentration of oxygen. He interpreted his observations by assuming that there existed an improved availability of trace elements within a context of low oxygen values, and furthermore that oxygen can be disposed of more easily by the plant and that the plant has to use up less energy in the course of maintaining its internal redox milieu.
> 
> According to Krause the energy requirements of a plant to maintain a low redox voltage will rise proportionally to the level of oxygen concentration in the surrounding water.


Is this the real reason that we are told not to aerate planted aquarium water?


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## Daemonfly (Mar 21, 2004)

So, how would one keep low O2, high CO2, and healthy fish in a tank? Good conditions for plants will make them produce much more oxygen. If you try to remove the oxygen by common means, you lose CO2 as well.

How low is low? Low enough to be detrimental to fish health?


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## Phil Edwards (Jan 22, 2004)

I would argue that it's not as much related to trace elements and RedOx, as it is with the photosynthetic pathway of the plants. 

I'm pretty sure that most of our aquarium plants are of the C3 variety, mening they do most of their photosynthesis within the spongy mesophyll later in the middle of the leaf. Hopefully Paul and/or Sean M. will be able to shed some light on this. One of the problems with photosynthesis is that O2 bonds easily with RuBP and often blocks uptake of CO2. In C3 plants as photosynthesis continues, the O2 levels inside the leaf increase making it more likely that O2 will bond to the RuBP vs. CO2. C4 plants take an extra step and actively transport CO2 into the bundle sheathes surrounding the vascular tissues so O2 interference isn't much of an issue. 

As far as RedOx goes, we put so many chemicals into our aquarium that the RedOx potential of everything is way screwy. I don't doubt that with higher O2 levels chemicals in the water column are more easily oxidized, but within the plant itself it's not an issue. The issue within the plant is the O2 levels in the leaves.

My .02,
Phil


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## Maurici (May 31, 2004)

There are site competence at the rubisco level between CO2 and O2, but is not an easy issue regarding the existence of various possible C concentrating mechanism from DIC which leds C disposable to make photosynthesis. Many plants of our aquariums are something like CAM type, with more importance of PEP-carboxilase for the C incorporation. At the same time there are other limitants of photosynthesis which can play a more crucial role than a punctual increase of O2 levels in difficulting to obtain the optimal of methabolic primary production. So, the relation CO2 consumption-O2 production with light and O2 consumption in the night is not an equation with easy stablishment of percentages involved to promote direct quantification of photosynthesis rate.


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## plantbrain (Jan 23, 2004)

High O2 levels are toxic to most organisms, algae, plants, critters etc.
I think what he was pointing to was more an issue of photorespiration with O2 competiting for CO2 with Rubisco.

The trace part really is a non issue with redox. Chelators or substrate supply take care of that. Redox and O2 levels vary diurnally anyway in the water column quite a bit. 

I think he'd be very hard pressed to show evidence that O2 levels actually depress growth in submeresed aquatic plants due to redox and trace limitation.

Let us hear some figures about this and some support. 
Most will point to Photorespiration and O2, not traces/redox.

I've done gas analysis with aquatic plants and algae. I did not find any research showing support for this claim on traces & redox. 

Many common aquatic plants do not have a spongy mesophyll layers at all. Egeria, Hydrilla etc.

Hydrilla is a C4 plants but does not have any Krantz anatomy.
The leaf is only 2 cells thick. It's a bicarb user but does so indirectly. 

Algae, plants, even some C3 plants etc have Carbon concentrating mechanisms that help improve the efficency of the Rubisco.

Lyngbya and Hydrilla for example can survive and do well at 200% O2 saturation levels, temps up to 40C etc.

Tough stuff.
Both can do just fine at high O2 levels and high temps.

Higher temps increases PR in many plants.
CAM, C4 etc are all basically the same, they use a 4 carbon acid to concentrate CO2 around Rubisco.

Traces are well...............traces........showing significant changes due to these will be tough to prove, wereas adding something like CO2, N etc to a very limited system will yield very significant results.

Aeration is fine for a non CO2 tank, adding it will increase CO2, wereas a CO2 enriched tank will blow off CO2 by doing this.
So that depends also on which type of plant tank you are speaking of. 

Regards, 
Tom Barr


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## Maurici (May 31, 2004)

Hi Tom, can you explain a little more your opinion that follows?


> Aeration is fine for a non CO2 tank, adding it will increase CO2, wereas a CO2 enriched tank will blow off CO2 by doing this.


12
Thanks. Maurici.


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## plantbrain (Jan 23, 2004)

"Aeration is fine for a non CO2 tank, adding it will increase CO2, wereas a CO2 enriched tank will blow off CO2 by doing this. "

Since a non CO2 tank can become very CO2 depleted with active photosythesis, aeration will allow more CO2 to come in from the surface and exchange the gas. CO2 saturation is lower in the water than the air above.

In a tank that has excess CO2 through enrichment, the aeration will blow off more of the CO2, there is more CO2 in ther water than in the air in this case. So CO2 saturation is higher in the water than the air above. 

Aeration will help to equilibrate the solution with the air's concentration.

Generally in natural systems and springs, there is always an excess of CO2, eg,the water is always giving off CO2. 

Regards 
Tom Barr


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## SCMurphy (Jan 28, 2004)

Pearling occurs when DO is saturated, if the O2 were harmful I think every pearling mass of riccia would have died off a long time ago. 

I can't state it any better than Kasselmann's book which has a write up of what she thought of that 'theory', which when viewed with Tom's reply should be enough to kill that one where it stood. Well, sat, since it didn't have a leg to stand on to start with.


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## Maurici (May 31, 2004)

Hello,


> Pearling occurs when DO is saturated, if the O2 were harmful I think every pearling mass of riccia would have died off a long time ago.


you are wright, Tom will correct me if I'm wrong but I think that "harmful" is not a good word to explain the difficulties which gives high levels of O2 to many organisms, mainly photosynthetics, because the inhibition of photosynthesis. I belive his contributition is concerned to the stop of this methabolism which would be dangerous if very high O2 concentration is maintained for a long time, but in the nature the O2 saturation is often only circunstancial and is merely a part of a ecosystem cycle when organisms and environment plays different and changing in time roles.
Best wishes. Maurici.[/quote]


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## plantbrain (Jan 23, 2004)

I have not found that high O2 prevents or hinders plant growth much, neither have Limnologist either. Same for algae, although perhaps some spores have a tough time growing when the there is high O2 and low CO2.

Photorespiration and the affinity for O2 by Rubisco was discovered by my old professor Dr Bowes. There's also a Russian guy that did a lot of work on PR in algae from the U of Moscow.

Most organisms have mechanisms of dealing with high O2 levels.

Regards, 
Tom Barr


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