CO2 Enrichment and Plant Nutrition

It was noted in previous posts that for crops with C3 photosynthetic pathway the current levels of atmospheric carbon dioxide are limiting to plant growth. Crops are currently starved of CO2 in a similar way to being starved of water, nitrogen, phosphorus, light etc. Current atmospheric levels of CO2 can thus be regarded as a plant stress, which weakens them and makes them inefficient. At higher levels of CO2 this stress is reduced, and the plant copes better with all other types of stress, including heat and cold, atmospheric pollution, root pathogens, as well as shortages of water, minerals etc.

Sylvan Wittwer (Professor emeritus at Michigan State University, who directed the Michigan Agricultural Experiment Station for 20 years and chaired the Board on Agriculture of the National Research Council) has remarked:

There has been and still remains, a great reluctance on the part of many climatologists and ecologists, and especially environmentalists, to accept the concept that the rising level of atmospheric CO2 could be more beneficial than harmful for plant growth, food production, and the overall biosphere…Yet the scientific evidence is overwhelming.

Summary data from 279 published studies is shown below in which plants of all types were grown under paired stress (red) and unstressed (blue) conditions. For resource-limited plants the benefits of increased CO2 are astounding.


Wittwer points out that of the hundreds of scientific reports documenting the benefits, Al Gore carefully selected five reports and a personal communication to emphasize possible negative aspects to enhanced CO2 on plants. Gore knew what he was doing, of course – he either deliberately rejected the facts, or gave instructions to researchers for his book only to cherry pick papers that support his alarmist agenda. Again we see him as a lying propagandist.

In Physiological plant ecology: ecophysiology and stress physiology of funcional groups (Springer, 2003), Walter Larcher writes:

According to over 3000 scientific publications on the biology of CO2 effects, a broad spectrum of growth responses to CO2 enrichment exists. Since elevated CO2 often reduces the plants’ demands for other resources, CO2 effects on growth do not simply follow Liebig’s law of the minimum. Plants exposed to elevated CO2 need less enzymes (and thus lower quantities of leaf proteins and nitrogen), lose less water (can cope with less soil moisture and often operate at smaller stomata openings) and need less light (because of a shift in the light compensation point for photosynthesis) to reach the equivalent, or even higher photosynthetic rates than plants growing under control conditions with “normal” CO2 concentrations.

We will show from the literature the tremendous benefits of enhanced atmospheric CO2. The benefits are much more marked in crops that are subject to resource limitation. Under ideal conditions, where there is no shortage of water, light, nutrients, trace elements etc, the benefit of doubling atmospheric CO2 may be 40%. However, where plants are resource limited a doubling of CO2 can enhance growth of crops by over 100% in some cases. This is particularly important in regions of the world where the soil is poor for many reasons, since increasing atmospheric CO2 will enable crops to be grown efficiently where they currently cannot be grown without first improving the soil and irrigation. In this post we will briefly mention minerals and other essential nutrients (nitrogen, phosphorus, iron etc).

For example, iron deficiency is severely limiting to crop growth in calcareous soils, which represent 30% of global land area. Increased atmospheric CO2 enables plants to extract higher levels of iron from the soil. Jin et al in Elevated Carbon Dioxide Improves Plant Iron Nutrition through Enhancing the Iron-Deficiency-Induced responses under Iron-Limited Conditions in Tomato (Plant Physiology, May 2009) demonstrated

Plant growth was increased by elevated CO2 in both Fe-sufficient and Fe-limited media. Shoot fresh weight was increased by 22% and 44%, respectively, and root fresh weight by 43% and 97%, respectively, compared with plants grown in ambient CO2…

Improved nutrient and water uptake has in some cases been traced to greater root mycorrhization (a symbiotic fungal extension of roots). Mycorrhizae also improve plant health by protecting roots from pathogenic microorganisms.

In Effect of Carbon Dioxide Concentration on Growth and Dry Matter Production of Crop Plants (Japan. Jour. Crop Sci, 1978) Imai and Murata showed that after 10 days of treatment with nitrogen at 350ppm and 1000ppm CO2 the dry weight (DW) of rice plants was as follows:

350ppm CO2, 30 mg nitrogen per plant DW = 835 mg per plant
350ppm CO2, 120 mg nitrogen per plant DW = 1,081 mg per plant
1000ppm CO2, 30 mg nitrogen per plant DW = 1,199 mg per plant
1000ppm CO2, 120 mg nitrogen per plant DW = 1,862 mg per plant

This demonstrates that at higher levels of atmospheric CO2, food crops have considerably lower requirements for fixed nitrogen for the same growth; alternatively, for the same nitrogen treatment they achieve considerably enhanced growth.

Higher levels of atmospheric CO2 lead to greater biological nitrogen fixation from the atmosphere, so less is required to be added as fertilizer. This is especially important in legumes, which are also able to improve their uptake and usage of phosphorus with increased CO2. Legume /bacterial symbiosis leading to nitrogen fixation is significantly increased at elevated CO2 levels (Reddy et al, 1989; Reardon et al, 1990). Philips et al (1976) demonstrated increased nitrogen fixation in peas, and Sherwood (1978) found the same in clover. A classic study by Hardy and Havelka (1975) showed that a tripling of atmospheric CO2 results in a six-fold increase in biological nitrogen fixation (from 75 to 425 kg per hectare) by rhizobial bacteria in nodules attached to the roots of soybeans.

Increasing atmospheric CO2 is an unmixed blessing – it will bring currently unproductive land into use and bring greater yield from existing land without additional fertilizer use. This is a wonderful benefit in being able to feed an increasing world population. These effects can be subjected to routine experiment and observation, can be demonstrated and reproduced, and so are sound science, unlike the specious pseudo-science underpinning the supposed effects of CO2 on climate.

12 Responses to “CO2 Enrichment and Plant Nutrition”

  1. 1 Ed Darrell August 15, 2009 at 1:28 pm

    Limitations on plant growth, generally, in order:
    1. Water
    2. Nitrogen
    3. Sunlight
    4. Carbon

    Some new croplands will be opened, but not always in prime areas. For example, the vast prairies of North America, in Canada and the U.S., are prime wheat growing fields because they were prime grass-growing areas previously. Soils and water were just right.

    In contrast, the North Panhandle of Texas only has the water part of the time — and opening it to wheat resulted in The Dustbowl.

    Still, those crops are, in modern agriculture, heavy users of fertilizers. Nitrogen fixation may increase, but not all plants are legumes. Grasses are not legumes, for example, which include all the cereal grains. Clover isn’t much good as a commercial crop. Alfalfa goes to provide hay for livestock.

    So if we’re increasing wheat and barley and corn, or other human-edible crops, we’re not reducing fertilizer needs.

    Rice? Well, it’s a water-loving crop. While it’s possible to grow it without flooded rice paddies, it’s not going to do as well in Wisconsin as it does in Arkansas.

    And can we talk insects for a moment? Warming allows the pine borers to work year around, killing pine trees up to ten times more efficiently than when we have winters cold enough to slow them down. Dead trees don’t sink carbon dioxide at all, they add to the load in the air, and they increase warming.

    Sure, in a few cases, CO2 will benefit crops. In many more cases it will benefit weeds more, the increased heat will make the crops unproductive, and insects will wipe out any potential gains.

    I don’t know of anyone who is reluctant to discuss crop benefits from CO2 among serious climate, weather and agricultural scientists. However, they realistically look at the situation, and they conclude that it’s a fool’s errand to try to make a case that warming is a good idea. We’re not going to plow under Canadian forests to grow wheat as plant zones move north, and replacing Kansas wheat with Mexico’s blue agave seems like a bad trade-off — except that it might increase the production of tequila that farmers can use to drown their woes as their farms go bankrupt.

    And so far as I’ve seen, you’ve failed to account that increased carbon dioxide generally favors weeds over domesticated crops.

    ScientistForTruth responds

    You are mixing two things together. A lot of what you are saying assumes that the increasing CO2 concentration will cause significant warming, but there’s no robust scientific mechanism or evidence for that. On the other hand, there is an abundance of evidence for the benefits of elevated CO2 on food crops, and it is scientific and easily testable. For C3 crops I have shown in former posts that they will increasingly outcompete C4 weeds (which globally are the most troublesome weeds for C3 crops) as CO2 concentrations increase.

    For the USA, the agriculture section of the report Climate Change Impacts on the United States did model simulations based on the Hadley and Canadian scenarios for 2030 and 2090 for 16 crops, and, of course, those are taking account of warming scenarios. They show dramatic improvements in crop yields, some of them over 100%, and in the overview they state

    “…at the national level, productivity of many major crops will likely increase under the climate scenarios used in these crop models. Crops showing generally positive results include cotton, corn for grain and silage, soybeans, sorghum, barley, sugar beets and citrus fruits.”

  2. 2 Michael Babbitt August 16, 2009 at 7:15 am

    You can see the weasel words in a lot of AGW propaganda: “may”, “likely”, “could”. Because the science is so shoddy and nonconclusive and only tied together by a AGW perspective of a “possible” global catastrophe. I am more convinced now that more C02 leads to a slightly warmer planet with a much more robust Biosphere. (This could or could not result in positive or negative changes to our world.)

  3. 3 Ed Darrell August 16, 2009 at 10:23 pm

    ScientistForTruth says

    I have cropped this extremely long comment from Ed Darrell as most readers will otherwise probably give up before getting to the end.

    Ed Darrell says

    The report said:

    At the national level,the models used in this Assessment found that irrigated agriculture’s need for water declined approximately 5-10% for 2030 and 30-40% for 2090 in the context of the two primary climate scenarios, without adaptation due to increased precipitation and shortened crop-growing periods.

    Oh, yeah, productivity will increase while the plants grow, but only two alfalfa crops a year instead of three — maybe no corn crop, maybe no wheat, sorghum, soy or barley. Ouch. The growing season is shortened, so total production through the year will be less on those crops.

    ScientistForTruth responds

    This commentator seems not to understand the difference between ‘growing season’ and ‘growing period’. A shortened growing season means that the number of weeks in the year that crops can be grown declines (very northerly latitudes have short growing seasons). A shortened growing period means that the time from sowing to harvest is reduced, so it can be possible to plan for more crop harvests per year. This is what is meant in the report, and it is the complete opposite of what this commentator thinks the report says. This would have been obvious to anyone acquainted with plant physiology as the report (in the section quoted above) is showing significant improvements in water efficiency, which come from reduced transpiration for two reasons: higher CO2 levels closing the stomata, and fewer elapsed days for the transpiration to occur due to shorter growing period. Had he read the report more carefully the commentator would have also noted that the report clearly states, in the context of adaptation:

    Sowing dates and other seasonal changes
    Plant two crops instead of one or a spring and fall crop with a short fallow period to avoid excessive heat and drought in mid-summer. For already warm growing areas,winter cropping could possibly become more productive than summer cropping.

    Ed Darrell says

    As to your bizarre claim that there is no “robust” indication that CO2 causes warming, I can only conclude that you’ve never studied chemistry or physics, or maybe either, and that you know nothing about meteorology and greenhouse gases. The greenhouse chemistry of CO2 has been well understood for about 20 years; the effect obtains if the sun shines and no other pollutant gets in the way. It’s a chemical/physical reaction about as certain as the fact that combusting hydrogen and oxygen will result in the creation of water. I suppose there’s a chance that God will intervene at some moment and miraculously change the chemistry of the universe, but I’m not a rash gambler, and it’s not a good idea to bet on such miracles.

    ScientistForTruth replies.

    This commentator can only conclude that I’m ignorant of chemistry and physics because he doesn’t seem to understand these subjects himself (for those readers who know who I am, his comment will come as rather fantastic). He claims to be competent in biological sciences, but to mix up crop growing periods with seasons weakens his case on that science as well. Comprehension skills also seem to be lacking as I made no claim that ‘there is no “robust” indication that CO2 causes warming’ but that there’s no robust scientific mechanism or evidence that increasing CO2 concentration will cause significant warming. There’s a world of difference between no effect and an effect that is not significant. The fact that CO2 absorbs infrared radiation is covered in my post Greenhouse Nonsense. But to extrapolate from laboratory spectroscopy to global warming so as to state that global warming is as certain as the reaction between hydrogen and oxygen displays ignorance. For a start ‘warming’ refers to temperature not heat, and spectral absorption is dealing with energy not temperature. Moreover, the small amount of energy absorbed by increasing CO2 is not sufficient significantly to warm the planet. To say “The greenhouse chemistry of CO2 has been well understood for about 20 years; the effect obtains if the sun shines and no other pollutant gets in the way” is actually almost irrelevant because the impacts projected in the IPCC reports don’t rely on simple CO2 ‘greenhouse chemistry’ but on huge positive feedbacks in other atmospheric systems which are certainly not well known, and are currently unproven. The comparison with hydrogen and oxygen forming water is thus inane. Finally, we don’t need to invoke a miracle to keep the planet cool. If God sustains the established laws of physics and chemistry then we shall not see any significant warming – by this I mean that we will not be able to distinguish any anthropogenic effect from natural variation with statistical significance.

  4. 4 Dan Absher September 23, 2009 at 7:59 pm

    Considering that we have a sleepy sun, a possible upcoming grand minimum, which if it happens will be accompanied by more cloudy days and less sunlight reaching the earth, with shortened growing seasons, a large increase in atmospheric CO2 content would be very beneficial. A shortened growing period would be welcome. A short description is here:

  5. 5 Gordon Sirmond February 5, 2011 at 9:19 pm

    I will admit to not having read the wole work, only the 14 page summary on SPPI site.

    Click to access 55_benefits_of_co2_pamphlet.pdf

    Points 21 to 23 attribute increased human longevity to increased atmospheric CO2. Unfortunatley I was ignorant enoughto believe that that was down to improvements in public health and medicine. Still you live and learn

  6. 6 Gordon Sirmond February 5, 2011 at 9:41 pm

    Further to my last post – if CO2 at present atmospheric levels is limiting plant growth then why is atmopsheric CO2 increasing and why is this extra carbon not being utilized by plants? Why aren’t plants in “the wild” growing faster?

    Hope you can explain

    ScientistForTruth responds:

    The extra carbon is being utilized and the plants in the wild are growing faster. A full 30% of the agricultural yield improvements in the twentieth century can be attributed to rising CO2 levels. If we were to reduce CO2 levels to where they were 100 years ago, so reducing yield by 30%, it would probably wipe out 500 million persons this year: there are already 1 billion persons in the world barely surviving.

    The increase in the rate of growth of forests due to higher CO2 is tremendous and has been noted in the literature. If plants were not sinking CO2 faster then the atmospheric concentration of CO2 would be higher.

    The rate that the developing world is increasing CO2 emissions (look at China and India) is faster than the increasing rate of uptake of plants, so the concentration keeps rising.

  7. 7 Gordon Sirmond February 9, 2011 at 7:36 pm

    Right, so stomata close in response to increased levels of CO2. Presumably this is to prevent acidification of the interior environment of the leaf, or can ypou think of another reason. Reduced stomatal opening will result in reduced gaseous exchange with the atmosphere. So the plant is acting to reduce uptake of atmospheric gases – so how does increased atmospheric CO2 increae yield when plants actively reducing gaseous exchange. And arent the levels of CO in the atmosphere still blow those necessary to increas yields in glasshouses?

    Could you explain please?

    ScientistForTruth responds

    There is a continuous increase in plant growth and yields from suffocation levels around 250ppm up to at least 1000ppm, and much higher for many plants. Greenhouses often operate at 1000-2000ppm CO2. Any increase all the way up from our present levels to at least 1000 ppm is going to be beneficial to plant life.

    Plants lose a lot of available energy in transporting water to leaves, only for that water to be lost when the stomata are open. C3 photosynthesizers also lose a lot of carbon that they have captured when the stomata are open. Think of it in terms of partial pressure or osmosis. When the partial pressure of CO2 in the atmosphere increases and the stomata close the ingress rate of carbon may be similar, but the egress rate of carbon and water decrease, so the net effect is highly beneficial.

  8. 8 Gordon Sirmond February 9, 2011 at 7:40 pm

    I forgot to include this but

    “The rate that the developing world is increasing CO2 emissions (look at China and India) is faster than the increasing rate of uptake of plants, so the concentration keeps rising.” which must surely tell us that the increase of CO2 in the atmosphere has gone past the point at which it had any benefical effects

    ScientistForTruth responds

    No, it doesn’t surely tell us that at all. If the rate of emissions increase exceeds the rate of uptake increase then the atmospheric concentration will keep rising, and as it does so the uptake rate will keep increasing. So long as the partial pressure of CO2 keeps increasing (i.e. we deliberately keep ramping up our emissions) then yields will keep increasing.

    We need these yield benefits – by 2050 there are expected to be 3 billion more mouths to feed on this planet; there are already a billion on starvation existence. Increasing carbon emissions has an important role to play in sustaining mankind. Should we be so foolish as to reduce carbon emissions then we will consign many billions to death. I have no doubt that this is an ulterior motive behind moves to reduce carbon emissions, a sort of Malthusian ‘Final Solution’. It will make Hitler’s 6 million exterminated look a minor affair.

  9. 9 Kimbal February 14, 2011 at 5:37 am

    The tiny portion of CO2 in the atmosphere is simply not capable of having an impact on temperatures. Furthermore CO2 is not a pollutant, it is plant food. Even if CO2 could warm the planet, this would be beneficial rather than detrimental. We know the Middle Age Warming Period was a time of plenty for the Northern Hemisphere, a time when Greenland and Coastal Canada was hospitable to crops and herd animals, a time when grapes grew well in England! No coastal cities were flooded, there were not massive horrific storms ravaging the globe, there was just more food and milder winters.

  10. 10 Gordon Sirmond February 16, 2011 at 6:52 pm

    And as for this comment

    “Should we be so foolish as to reduce carbon emissions then we will consign many billions to death. I have no doubt that this is an ulterior motive behind moves to reduce carbon emissions, a sort of Malthusian ‘Final Solution’. It will make Hitler’s 6 million exterminated look a minor affair.”

    You should hang your head in shame for having ever typed that let alone published it

    ScientistFor Truth replies

    You must be kidding. I’m not ashamed of pointing out greater sins. Which is the greater evil, exterminating some billions by deliberately cutting back on a life-giving gas that is necessary for their sustenance, or exterminating some millions directly with toxic gas? It’s obvious I’m making a comparison.

  11. 11 Darlea Henderson June 19, 2011 at 7:14 pm

    How do I reply to the people that buy into CO2 being bad. They say that the CO2 that is manmade is a heavier isotope than regular CO2 and this is how they get around the argument that it is good for plant growth. Are there any experiments that show CO2 with different isotopes doesn’t impact the environment?

    ScientistForTruth responds

    These people are either very misinformed, or are trying to mislead you. There are three carbon isotopes C12, C13 and C14. C14 is radioactive and present in only tiny quantities so we can ignore it. C12 makes up around at least 99% of the carbon in the atmosphere, in plants, in carbonate rocks, and in fossil fuels. The balance is C13, the heavier isotope. The differences between the amounts of C13 in all these different carbon carriers is a lot less than 1% of the total carbon. CO2 in the atmosphere is slightly richer in the heavier C13 than in the emissions from fossil fuels, but neither is more than 1% anyway.

    Plants slightly prefer to take up C12 over C13, so since carbon emissions from burning fossil fuels are composed of more than 99% C12 (and slightly richer in C12 than atmospheric CO2) then they are excellent plant food. In fact, the concentration of C12 in carbon emissions from burning fossil fuels is a fraction of a percent richer than in atmospheric CO2, so is correspondingly a fraction of a percent better for plants. But, frankly, since we are talking about fractions of a percent difference it is almost completely irrelevant with regard to growth rates.

    Of course, carbon emissions are being vented to atmosphere, so over the decades the percentage concentration of C12 in the CO2 in the atmosphere is actually slowly increasing from its present level of around 99% of the isotope favoured by plants. The most favourable concentration would be 100% C12, and carbon emissions are closer to that ideal!

    So as carbon emissions continue the increasing concentration of CO2 itself within the total mix of the atmosphere favours plants (dramatically), and the increasing proportion of C12 within the CO2 fraction also favours plants (very slightly). Burning fossil fuels is excellent to be able to help feed the world in the coming decades.

  12. 12 Peter Messenger June 6, 2012 at 8:49 am


    I am but a simple layman, but I have found this blog delightful and informative. The discussions seem measured without the SHOUTING normally coming from both sides of the AGW fence.

    I am becoming ever more sceptical as I dig deeper and appreciate sites such as this to further my overall education.

    I cannot add to the discussions (particularly regarding mathematics :-)) but thought you might find this of interest and relevant to this part of the blog.

    I understand from the news this morning that the site is now up and running but, as a layman, I can’t honestly believe that this in any way represents a valid eco-system for the purposes of settling the AGW debate.

    I would like your thoughts on it.

    ScientistForTruth responds

    Thanks for your encouragement. The experiment you mentioned cannot tell anything more than the possible effects of elevated CO2 on a particular forest. If properly conducted it might produce some useful insights. Lots of studies have been done in laboratories and under controlled conditions to determine the effect of CO2 on plants, so this is just another, and at a larger scale. Of course, the results will only have a minor application to the AGW debate.

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