Doubling of CO2 will cause global plant photosynthesis to increase by a third

Discussion in 'Earth Science' started by Plazma Inferno!, Sep 29, 2016.

  1. Plazma Inferno! Ding Ding Ding Ding Administrator

    Vegetation and soil are currently slowing down global warming by absorbing about a quarter of human emissions of carbon dioxide (CO2). This land carbon sink is believed to be in part due to increases in photosynthesis. This new study in the journal Nature shows that doubling of the CO2 concentration in the atmosphere will cause global plant photosynthesis to increase by about one third. As well as its role in the climate system, photosynthesis also provides the primary food-source for life on Earth. The study therefore has relevance to the future health of ecosystems, as well as to the challenge of slowing climate change.
    The research was carried-out by scientists from the German Aerospace Center (DLR) and the University of Exeter in the UK, in a collaboration supported by the European Union through the CRESCENDO project.

    Interesting. But I wonder what would happen if temperatures rise due to increased CO2? Doesn't photosynthesis shut down when temperature is too high?
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  3. sculptor Valued Senior Member

    Much depends on the plant.
    On average C3 plants will have an increase of 41% growth with a doubling of CO2, while C4 plants will only increase by as little as 22%.
    Along with the increase in growth we will have a shortening of time to maturity of up to 20%
    C3 plants can maintain efficient photosynthesis rates at considerably higher temperatures than today’s conditions – their optimal temperatures for photosynthesis increase.
    At low-normal co2 concentrations, C3 plants usually have peak production between 30 and 40 degrees C, while at higher concentrations of CO2 the optimum temperature increases to the high 40s C.
    C4 plants normally are much less cold tolerant, and do not show a like response to CO2 increase(22 vs 41%), but are by nature more heat tolerant.

    Simply put: Primary producers were here first, and have been here much longer. They have survived and evolved through much higher and lower CO2 levels and concomitant temperature variations.
    Last edited: Sep 29, 2016
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  5. iceaura Valued Senior Member

    This figure of 1/3 is not a newly discovered effect or unexpectedly large influence, it is a constraint on what have been model estimates ranging as high as 60%. It is closer to the more "conservative" end of the range being employed in modeling this stuff - the former range was 20 - 60, by this evidence and reasoning it should be 25 - 40 or even tighter.

    So far.

    That projects to an increased likelihood of severe temperature effects from the CO2 emissions - the models that assumed the fastest uptake and smallest boost in levels are in the most conflict with this analysis.

    Also, unless I'm reading wrong these results do not allow for significant curbs on CO2 uptake by either temperature increases (especially night) or increased range of variability in the weather.

    There's also this: which suggests that boosting carbon uptake by CO2 fertilization of oceanic photosynthesizers might actually increase, rather than decrease, the water temperature boost of a given atmospheric CO2 level.
    Last edited: Sep 30, 2016
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  7. synthesizer-patel Sweep the leg Johnny! Valued Senior Member

    Double post
    Last edited: Dec 8, 2016
  8. synthesizer-patel Sweep the leg Johnny! Valued Senior Member

    Triple post - FFS!
  9. synthesizer-patel Sweep the leg Johnny! Valued Senior Member


    In general, oceanic primary production isn't carbon-limited - there have been a few studies that have shown areas that have extremely low PP - like in the centre of oceanic gyres - to experience raised PP with increased carbon input - but those are atypical - and you're basically going from nearly nothing to nearly nothing x2 - no big deal.

    The oceans are, at least for now, a net sink for carbon - there's plenty there in an available form, far more than can gets used by primary producers - adding more won't make much difference - because the limiting factor is the availability of micronutrients like bio-available nitrogen, iron, phosphorous etc - not carbon

    I was under the impression that terrestrial primary production was similarly limited - but I don't profess to any expertise at all on that
  10. iceaura Valued Senior Member

    This guy's stuff is worth checking out:

    One of his takehome lessons (for me) was that the supply ratios of critical nutrients (rather than the absolute supply) explain a great deal, and are a primary arena of competition among plants (you can find an elegant theoretical analysis involving supply ratio growth curves and the like in his earlier stuff). At one time I was trying to extend his approach to things like variation in factors - considering variation itself as a "nutrient", and extending the factors considered to temperature and water (so temperature variation in some kind of units would be treated as a nutrient is treated in Tilman's approach), but alas for the lost enthusiasms of youth.

    Another was that short term ecological responses to a major change are not reliable indicators of long term ones - the plants that initially benefit, and the plants that initially suffer, very often trade roles over the long run, and the ecosystem develops through significant changes over time.

    Couple of side points:
    On land temperature variation and water supply matter much more than in the ocean, and CO2 interacts with both. (Plants gain CO2 and lose water through the same holes, which they can control: the water budget in particular depends heavily on temperature, including temperature variation, the CO2 affects the temperature and the variation, and so forth. All this varies enormously by plant species and details of landscape).
    On land many plants - being superior competitors for a fairly narrow set of supply ratios etc - are geographically confined by competition, even across a fairly wide range. They will have to move - find new and likewise fairly confined places - if something major changes, not only from the effects of the new conditions but because they face loss of competitive superiority where they are (they won't be able to reproduce in competition). Considerations of abstract "primary productivity " conceal such matters. One word that keeps turning up in such discussions of Minnesota ecosystems is "sumac".

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