Guest post by Indur M. Goklany
This illustration from a recent article in Science magazine shows that CO2 is plant food. It is based on both empirical data and model results (not “data”). I know that looking at empirical data might seem like a novel idea to some people, but for some perverse reason, I find it more compelling.
On the right: Empirical Data. Growth of 21-day-old rice and S. viridis seedlings at different ambient CO2 concentrations ranging from 30 to 800 parts per million. NOTE: The very last set of pots on the extreme right is out of sequence. They are for 390 ppm, while the next to last pots are for 800 ppm.
On the left, Modeled Data:
Modeled changes in CO2 assimilation rate in response to changes in leaf intercellular CO2 partial pressure for C3 and C4 photosynthesis and for a hypothetical C4 rice. Curves 1, 2, and 4 have Rubisco levels typically found in a C4 leaf (10 μmol m−2 catalytic Rubisco sites). Curve 3 shows a typical response for C3 leaves with three times the Rubisco level of C4 leaves. Curve 1 shows the response of a C4 leaf with C4 Rubisco kinetic properties. Curve 2 models how a C4 leaf with C3 Rubisco kinetic properties would respond (a hypothetical C4 rice with C3 Rubisco kinetics). The comparison of these two curves shows the increase in CO2 assimilation rate achieved with C4 compared with C3 Rubisco kinetic properties within a functional C4 mechanism. Arrows to curves 1 and 3 show intercellular CO2 partial pressures typical at current ambient CO2 partial pressures for C4 and C3 photosynthesis. To generate the curves, model equations were taken from (11) and comparative Rubisco kinetic constants from (12). (B) [Reference numbers per source.]
Source: Susanne von Caemmerer, W. Paul Quick, and Robert T. Furbank (2012). The Development of C4 Rice: Current Progress and Future Challenges. Science 336 (6089): 1671-1672.
Finally, note that the top photograph on the right is for rice. According to Wikipedia, not always a reliable source, but in this case probably trustworthy:
[Rice] is the most important staple food for a large part of the world’s human population, especially in Asia and the West Indies. It is the grain with the second-highest worldwide production, after maize (corn), according to data for 2010.
Since a large portion of maize crops are grown for purposes other than human consumption, rice is the most important grain with regard to human nutrition and caloric intake, providing more than one fifth of the calories consumed worldwide by the human species.
In other words, not only is CO2 plant food, CO2 makes human food. Guess some folks skipped that biology class.
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I’m by no means an expert, but doesn’t the question about whether or not it is universally beneficial have something to do with the respiration model used by the plant in question, where not all plants are the same? The argument as I have heard it given is that one kind of plant benefits, but another does not or can even be hurt by it. One species of plant does not a sweeping generalization make either way…
rgb
the Mark of the Alarmist is the obsession in deleting from history (=”denying”) everything that was known before, even the most uncontroversial stuff like CO2 being “plant food”.
this is in order to demonize the molecule, so no positive can be described as coming out of it.
Robert, do you have a plant in question that is negatively affected by CO2?
I love the Living Histogram! Best data representation ever. Let the plants be their own graph.
Thanks for this article. I had seen C3 and C4 photosynthesis mentioned on this blog before, but never looked into it. According to Wikipedia, C4 plants evolved more recently than C3 (25 to 32 million years ago), have an advantage over C3 plants in arid, hot, and low nitrogen/CO2 conditions, and are common among grasses, e.g. food crops such as maize, sugar cane, millet, and sorghum.
http://en.wikipedia.org/wiki/C4_carbon_fixation#The_evolution_and_advantages_of_the_C4_pathway
Wiki predictably links C4 plants to climate change:
“Increasing the proportion of C4 plants on earth could assist biosequestration of CO2 and represent an important climate change avoidance strategy.”
Unless the “increased proportion” of C4 plants are long-lived species like trees, however, I don’t see the potential for much more “biosequestration”. Certainly maize and sugar cane grown for fuel ethanol don’t count.
I would like to repeat Alvin’s comment. Is Dr. Brown aware of any plants that are negatively affected by increased CO2? I’m not questioning that there might be some, but I can’t help but think that if there were any, the doomsayer chorus would have let us know about it long ago.
The more CO2, the faster the grass grows, the more CO2 produced by lawnmowers cutting the grass and by humans guiding them. I see nought but doom (;>)
That 800ppm rice looks like a very happy plant indeed! Does anyone know of a study investigating whether such bigger plants also have the same nutritional value per kg? After all, if the ‘twice the size’ plant only has half the nutritional value, the actual ‘gain’ to humanity could be zero. Anyone wanting to throw money at me to do the research can get my email address from WUWT … though it’s only fair to mention that my ‘tender loving care’ has killed chlorophytum (= ‘spider plant’, = grass!)
Robert Brown;
The Idso brothers have been studying this for quite some time and have a remarkable database on the matter. There is the odd plant species that is negatively correlated with CO2 increases, but the vast bulk of them are positively correlated.
http://www.co2science.org/data/plant_growth/plantgrowth.php
I have a question. If plants can take that much advantage of higher levels of CO2 (look at 800ppm), is there any implication that there must have been a time in the past where these plants evolved to the point where they could make use of those higher levels of CO2? Or is it that at lower levels, they’d need to be more efficient and the higher levels is just the plant’s reaction to having evolved in lower CO2 environments? Can any assertions be made one way or the other? It seems like some plants take definite advantage of CO2 and that this is the way they evolved. I would think that if they were more efficient at lower CO2 levels, that they would “suffocate” at higher levels (or not the excess at all), but they don’t work that way. At least, not at 800ppm or even 1200ppm. For many plants, 1200ppm seems to be optimal growth. From what I understand, it is common to find 2000ppm inside buildings, though it should be kept below 1000ppm when possible.
Are there any indications that higher levels were required for plants to evolve to the point where they can take advantage of those levels as seen in the experiment in this article? (And not cause adverse effects to the plants).
The empirical data histogram, if put in the correct order and extended to 1000ppm, might actually look like a hockey stick! That’s my model.
Why would they not model c3 from the evidence, or use the evidence to challenge their model references? Of course I, Willis and other cynics on WUWT know the answer.
omnologos says:
June 30, 2012 at 12:49 pm
the Mark of the Alarmist is the obsession in deleting from history (=”denying”) everything that was known before, even the most uncontroversial stuff like CO2 being “plant food”.
==============================================================
They have also managed to delete from history the experiment performed by an American physicist professor R.W.Wood (1909) demonstrating that no (or no significant) warming is possible by means of “trapped radiation”.
@MrX The only sensible explanation I can come up with is, has to do with the fact that, with higer CO2-concentrations, plants are able to reduce the size of the openings on their leaves, that take in CO2 (at daytime at least) and so lower the loss of H2O. Therefore plants that need the most H2O, or are vulnerable to H2O-loss, might profit more from higher CO2. But i’m not a biologist.
Surely the experiment was done using good, natural CO2. It’s the bad, man-made CO2, no doubt filtered out of the growing chambers built by big oil and coal money, which is destroying the planet.
From davidmhoffer on June 30, 2012 at 1:22 pm:
Brothers?
The Many Benefits of Atmospheric CO2 Enrichment
Press Release: 2 Feb 2011
Snippet: “The book is The Many Benefits of Atmospheric CO2 Enrichment, written by the son/father team of Craig D. and Sherwood B. Idso.”
We’ll let it slide this time, but if you ever similarly call the Pielke’s “brothers” we’ll be forced to promptly kick you out of the Skeptic’s Clubhouse and tear up your membership card.
Me and my green friends demand 1200 ppm.
Can anybody here hand-deliver a copy of this report to the head of the EPA (Lisa Jackson)?
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Most plant species evolved during times of much higher CO2 concentration. At the historical level of 280 ppm, they were near starvation. ( At about 100 ppm some species die).
C4 type metabolism is a relatively recent invention and lets plants survive in lowering CO2 levels.
As a result, C3 plants respond more to increases in CO2 than do C4 plants.
In general, the increase in yields and growth continues to about 1000 ppm / 2000 ppm range (which is about where it was when the c3 plants were dominant).
The planet has been sequestering CO2 to excess as carbonates for so long that the plants were on the verge of dying. Their breathing a sigh of relief and getting back to normal (higher) growth rates as CO2 rises is clear evidence of that.
A forest or a bamboo plot will clear 100% of the CO2 above it in short order if allowed to grow.
http://chiefio.wordpress.com/2010/10/10/got-wood/
So world plant growth “limits” on CO2 as the limiting nutrient unless someone puts a lot more into the air or forest fires burn…
I would like to repeat Alvin’s comment. Is Dr. Brown aware of any plants that are negatively affected by increased CO2? I’m not questioning that there might be some, but I can’t help but think that if there were any, the doomsayer chorus would have let us know about it long ago.
As I said “I’m not an expert…” — I’m a physicist. However, I remember at least one CAGW-believing individual who asserted that there are plants for which excess CO_2 is not beneficial. Then there are secondary problems — the CO_2 might be good, but a side effect of the CO_2 might be worse. That’s the argument concerning CO_2 uptake in the ocean and acidification — the idea that it might push the pH of the ocean out of acceptable bounds. I’m properly skeptical of the argument, but I repeat — one doesn’t need an experiment to show that 800 ppm CO_2 is good for at least some crops. It’s standard practice in many greenhouses to bump it to 1000-1500 ppm (and amusingly, pot growers all seem to take advantage of that to grow their valuable crops faster:-).
But just as excess water kill cactus, it is by no means implausible that some plants object to excess CO_2. And a single experiment does not prove that the result is generalizable in any venue, let alone one with millions of species in a staggering array of ecologies. I’m a general purpose skeptic, not just skeptical about CAGW…;-)
Overall, it is probably better to keep our CO_2 level close to “normal” quite aside from what one thinks about CAGW simply because our ignorance can kill us in this as in many things. It isn’t probable, I agree. But wow, sometimes improbable things happen (and sometimes we have the estimates of probability wrong!)
rgb
Greg, that statement would look just on the surface to go against common sense.
Of course, you are aware of, and do not deny, the GHG effect by water vapor, a much more plentiful constituent of the atmosphere than CO2 …
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Steve C – humans dont often eat the plant itself, we eat the seeds.
If the increased photosynthesis results just in an increased seed starch content then, if other things were equal, one would expect a proportional dilution of the other consituents ; protein and some minerals.
However if the increase energy surplus enabled greater root exploration then this might offset a small proportion of this dilution, but overall there will be dilution.
However ‘starch’ is energy and whilst most of the western world’s problem is overconsumption of such stuff, to those short of food energy is a primary nutrient.
The increased photosynthesis (or reduced plant respiration) might be expected to increase the nitrogen fixing of legumes – who trade energy for protein with the organisms in their nodules. So increasing the general supply of protein – very important to those short of food.
So the gain to humanity is very much more than zero, but as you say the increase in supply of some other nutrients might be zero or small.
Most plant species evolved during times of much higher CO2 concentration. At the historical level of 280 ppm, they were near starvation. ( At about 100 ppm some species die).
One of the many risks of ice age — the low concentration of CO_2 in the last glaciation period was around 180 ppm. That really is getting too close for comfort, because before they die they fail to thrive… it is probably why we evolved plants that are more tolerant of low CO_2.
rgb
Too obvious for some
@ur momisuglyChas – (blush) Yeah, actually I’d sussed it was the seeds we actually eat (from every bag of rice I ever bought!) … the important thing here is finding somebody with a stack of spare cash … 😀
No, no. CO2 is what plants breathe in. Articles that continue to express belief in AGW are plant food.