Amazon fires: Oxygen supply not threatened

[QuantumT]

According to Scott Denning, prof. of Atmospheric Science at Colorado State University, we don't need to worry about the world's oxygen supply, despite of the thousands of wild fires in the Amazon and other places around the world.

https://theconversation.com/amazon-fires-are-destructive-but-they-arent-depleting-earths-oxygen-supply-122369

[mistermack]

That should be obvious, from a basic reading of the composition of the atmosphere. The air contains  20.95% oxygen, and 0.04% carbon dioxide. If you were to DOUBLE the current carbon dioxide, you would only need the tiniest fraction of the available oxygen to achieve it. It doesn't need a prof. of Atmospheric Science to work that one out.

In addition, the raising of CO2 levels would aid photosynthesis in the ocean, pumping more oxygen back into the atmosphere. 

[CharonY]

49 minutes ago, mistermack said:

In addition, the raising of CO2 levels would aid photosynthesis in the ocean, pumping more oxygen back into the atmosphere. 

Why would it? CO2 is not involved in oxygen production.

[mistermack]

50 minutes ago, CharonY said:

CO2 is not involved in oxygen production.

[CharonY]

 

4 minutes ago, mistermack said:

I would encourage you to read up on the light-dependent reaction and then the  Calvin cycle. One produces oxygen, the other does not. Extrapolation from erroneous assumptions tend to be inaccurate.

[mistermack]

2 minutes ago, CharonY said:

I would encourage you to read up on the light reaction and then the  Calvin cycle. One produces oxygen, the other does not. Extrapolation from erroneous assumptions tend to be inaccurate.

I would encourage you to explain your claim, and not dodge the issue with recommended reading.

[CharonY]

16 minutes ago, mistermack said:

I would encourage you to explain your claim, and not dodge the issue with recommended reading.

I am not dodging, just stating the obvious and asking you to clarify your initial claim (after all it was your comment, not mine). But since apparently you are not willing to look into it:

The light dependent reaction is what generates energy. During that process water splitting occurs, which releases oxygen. CO2 is not involved in that particular process and increase in CO2 does not change the rate of this reaction.

CO2 plays a role in a different, independent reaction, called the Calvin cycle. Only here CO2 is fixed. While it utilizes energy, including from the light-dependent reaction, it is mechanistically not coupled. Thus, CO2 fixation does not release oxygen. Here CO2 increase can result in higher fixation rate, when CO2 is the limiting factor. While that is often the case in C3 plants, in the ocean macronutrients are expected to more limiting.

Now, you could have meant in your statement that and increase in CO2 could potentially increase plant biomass, which then could result in an overall higher photosynthetic rate.  That would depend on a number of other factors, with the ultimate limit being how much light-dependent reactions could occur (e.g. light availability and sufficient micronutrients for chlorophyll production, temperature, etc.). That is why I asked for clarification.  However the depicted cartoon indicates  that you may have indeed assumed a direct connection,  which, as noted in my first comment, is simply incorrect. 

[mistermack]

1 hour ago, CharonY said:

CO2 is not involved in oxygen production.

The "cartoons" come from wikipedia's main page on photosynthesis.   https://en.wikipedia.org/wiki/Photosynthesis  

 

[CharonY]

 

6 minutes ago, mistermack said:

The "cartoons" come from wikipedia's main page on photosynthesis.   https://en.wikipedia.org/wiki/Photosynthesis  

 

Then hurry up and read the both sections i mentioned (light-dependent reaction and Calvin cycle). It should clear up the confusion you still have. Just to specify, the depicted photosynthesis are the result of two different reactions that are separated by time and space.

To be fair, that level of misunderstanding is not that uncommon, I blame highschool for that. Well, also the fact that those simplifications do not provide the required level of understanding. It matters little that they are on wikipedia, if the rest of the articles is not read (or perhaps it is written poorly, have not checked that).

Edit: nope the reactions and the interactions between those reactions are depicted just a bit lower. So the article is fine.

[mistermack]

2 minutes ago, CharonY said:

To be fair, that level of misunderstanding is not that uncommon, I blame highschool for that.

I think it's you that should be reading up on what the word "involved" means. 😊

[CharonY]

2 minutes ago, mistermack said:

I think it's you that should be reading up on what the word "involved" means. 😊

Unless you have a new definition of involved I do not see it. CO2 is not part of the reaction resulting in oxygen. Heck it is even in the wiki article (it is basically just one cartoon further down). Let's just agree that it does not work and move on. I am astonished why folks really do not like to inform themselves, though.

[mistermack]

I'm not disputing whether there are two different reactions. I'm disputing your assertion that they are not involved with each other. 

[Dagl1]

@CharonY, I am not super familiar with these reactions (high school was the last time I have heard about the Calvin cycle), but after reading up on them I am wondering if I understand this correctly; 1. the light-dependent reaction (oxygen production) could occur and continue forever in the absence of the CO2-dependent Calvin cycle, if it would be efficient enough to produce sufficient quantities of ATP (2. the function for the Calvin cycle being mainly to convert unstable NADPH (+ other stuff) into (more) stable G3P which can then 3. further be utilised in respiration reactions to produce ATP and I am not entirely sure about this last part 4. but more O2 is produced than later used in respiration reactions or is the net production of O2 a result of the fact that more energy is stored in G3P than is used by the plants?) Then 5. if we would supply unlimited NADPH and ATP, the Calvin cycle could continue forever in the absence of light-dependent reactions?

If my interpretation is correct, then I think I also understand the dispute regarding "involved".

Thanks in advance!

[CharonY]

1) in principle yes. There is no functional connection between the two reactions which occur in different parts of the chloroplast. The light-dependent reaction can be seen as somewhat analogous (but inverted) to the respiratory chain, essentially an electron transport chain along a membrane, but in this case fueled by light rather than redox potential. The resulting proton gradient is exploited analogously for ATP formation and the terminal reductase provides NADPH. This process does not involve CO2 as a component. 

2) the major function of the Calvin cycle is to fix CO2 via RuBisCO (i.e. carboxylation of ribulose bisphosphate) the following reduction and regeneration steps are what costs ATP and NADPH. But of course the molecules do not know or care where they come from. 

3) however, in higher plants the internal membrane structure of the organelles hinder free diffusion, and especially NADPH has a fast turnover, so that in practice the Calvin cycle will mostly be fueled by products of the light reaction. Of course in photosynthetic bacteria, which in aquatic systems are generally dominant, the situation is obviously more diffuse (heh). In general this is a function of cellular anatomy rather than the biochemical nature of the reaction though.

4) Whether there is net oxygen production depends on the efficiency of the light-reaction. Respiration occurs on a fairly constant rate but when the photosynthesis rate goes down (e.g. due to lack of light), oxygen consumption can outpace the light-reaction. 

5) Yes, indeed. And in fact, we do not even need to supply them with anything as there are organisms that do just that there. Lithotrophs for example, generally rely on the Calvin cycle to fix carbon, without being able to perform the light-reaction (i.e. they get their energy and reducing equivalents elsewhere). Incidentally, In class I used to use photosynthesis as a prime example how a simple concept is actually fairly complicated once we move away from the single example they have seen in highschool (e.g. anatomic coupling vs chemical ones). Some students are more resilient relearn than others. The concept is quite important to dissect different cellular functions (as e.g. energy production vs carbon metabolism) which are often muddled together, and thereby leading to confusion when we start discuss more complicated metabolic pathways.

 

[John Cuthber]

20 hours ago, mistermack said:

I'm not disputing whether there are two different reactions. I'm disputing your assertion that they are not involved with each other. 

In principle, you could arrange for them to happen on separate planets

(No, I don't mean separate plants)

On 8/30/2019 at 4:31 PM, QuantumT said:

According to Scott Denning, prof. of Atmospheric Science at Colorado State University, we don't need to worry about the world's oxygen supply, despite of the thousands of wild fires in the Amazon and other places around the world.

Did he also say we don't need to worry about a plague of unicorns (which nobody was worrying about anyway).

[Ken Fabian]

On 9/26/2019 at 5:44 AM, mistermack said:

the raising of CO2 levels would aid photosynthesis in the ocean, pumping more oxygen back into the atmosphere. 

I don't think this is true because it is not as simple as more CO2 equals more photosynthesis; other factors come into play.  Changed pH impacts algae - and algae impact pH; if algae health declines the ability to (via enzymes they release) break down CO2 to carbonate ions and an important regulating factor in ocean pH is impacted negatively, in ways that are not good for algae. Water temperature is also a factor.

https://askabiologist.asu.edu/plosable/algae-ocean-acidification

Back to the Amazon - oxygen supply was never a problem that knowledgeable sources brought up; like a lot of poor information, News and Entertainment organisations -  for whom viewers/readers and clicks are more important than accuracy - are often responsible. They are inclined not to bother much with experts and fact checking.

Edited September 26, 2019 by Ken Fabian

[CharonY]

2 hours ago, John Cuthber said:

Did he also say we don't need to worry about a plague of unicorns (which nobody was worrying about anyway).

To be fair though, once those bastards settle in, it is almost impossible to get rid of them.

[Dagl1]

@CharonY thanks for the interesting + in-depth reply!

 

[mistermack]

On 9/26/2019 at 9:30 AM, Dagl1 said:

If my interpretation is correct, then I think I also understand the dispute regarding "involved".

It's easy to understand. It's like shooting someone, and claiming you weren't involved, because all you did was pull the trigger, it was the bullet that killed him. 

The two actions are separate in time and space. I've never heard such rot. 😅

[Dagl1]

1 minute ago, mistermack said:

It's easy to understand. It's like shooting someone, and claiming you weren't involved, because all you did was pull the trigger, it was the bullet that killed him. 

The two actions are separate in time and space. I've never heard such rot. 😅

I really don't see it that way now that I understand the whole thing, but I had the same feeling before looking into it and with the full explanation.

Do you not feel that because, as said, in some cases, the two cycles are independent, it is fair to say they are not (necessarily) involved with each other. Of course the word "involve" is vague, but from my perspective it seems like you are saying that two reactions that CAN be independent are still involved with each other, which is not true for ALL cases. Is digestion "involved" in the killing of the person (in your example). In some far fetched way it is, because digestion is necessary for you to have the energy to pull that trigger (this example is not a direct analogy to the light-dependent and -independent reactions, it is meant to indicate that the meaning of "involve" can be stretched). 

Not saying either interpretation is right or wrong, just my interpretation.

-Dagl

[mistermack]

1 hour ago, Dagl1 said:

you are saying that two reactions that CAN be independent are still involved with each other, which is not true for ALL cases.

You really have to twist everyday logic to the extreme to make that case. This thread is about the oxygen supply in the atmosphere. How much of that oxygen in the atmosphere do you calculate was generated WITHOUT the normal corresponding intake of CO2?  

Wikipedia must surely give a clue :   

[Dagl1]

6 minutes ago, mistermack said:

You really have to twist everyday logic to the extreme to make that case. This thread is about the oxygen supply in the atmosphere. How much of that oxygen in the atmosphere do you calculate was generated WITHOUT the normal corresponding intake of CO2?  

Wikipedia must surely give a clue :   

I don't agree, but let's just agree to disagree on this;p.

[mistermack]

8 minutes ago, Dagl1 said:

I don't agree, but let's just agree to disagree on this;p.

Of course 😊

[Strange]

20 minutes ago, mistermack said:

You really have to twist everyday logic to the extreme to make that case. This thread is about the oxygen supply in the atmosphere. How much of that oxygen in the atmosphere do you calculate was generated WITHOUT the normal corresponding intake of CO2?

Although a more important factor is that most of the organic carbon formed from the CO2 is (or was) sequestered in a form that prevents it quickly reacting with oxygen again. So there are many other mechanisms that are involved in maintaining the oxygen level.

[mistermack]

Yes of course. The actual surplus oxygen that has built up over millions of years is the result of organics that turned into coal, or oil or gas etc, and was kept away from the microbes that would break them down using up the available oxygen in the cycle. 

If I remember rightly, there have been times when the oxygen levels were significantly higher, allowing giant insects like enormous dragonflies to exist. 

30 minutes ago, Strange said:

So there are many other mechanisms that are involved in maintaining the oxygen level.

But there's just the one involved in producing it. In significant quantities anyway.