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Can planting trees really reduce CO2 in atmosphere?

  1. Sep 10, 2015 #1
    From mycology books and articles, I read that most land plants (> 80 percent) on earth live in symbiosis with mycorrhizal fungi. In this symbiosis, plants provide glucose to fungi and fungi provide water and nutrients to the plants. Without fungi, plants cannot harvest nutrients in sufficient quantity directly from the substrate.

    Seeing as trees "eat" CO2 and fungi breathe it out, is the notion that humans could sequester our CO2 garbage by planting trees not somewhat suspect?
     
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  3. Sep 10, 2015 #2

    Bystander

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    In what way? You've omitted "residence time" of sequestered carbon in the trees and fungi from your consideration.
     
  4. Sep 10, 2015 #3
    @Bystander: in the sense of warding off climate change due to anthropogenic CO2. Whatever amounts that trees do absorb, we are exceeding that amount with fossil fuel emissions.

    Every tree will eventually turn into CO2 anyway, just due to saprotrophic fungi. But trees cannot grow without mycorrhizal fungi, which are respirators. I guess we'd have to know the rate at which the fungi that are in symbiosis with trees breathe out CO2, versus the rate at which trees eat CO2 and turn it into cellulose/hemicellulose.
     
  5. Sep 10, 2015 #4
    Surely a tree sequesters carbon while growing and releases it when it dies. It seems to me that at steady-state, even the Amazon jungle has basically zero effect on atmospheric CO2.
     
  6. Sep 10, 2015 #5

    Yes, but ANYTHING at equilibrium has no effect on the atmosphere.
     
  7. Sep 10, 2015 #6

    SteamKing

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  8. Sep 10, 2015 #7
    I would think that your model needs a slight improvement, but more on that later. As has been said, if in equilibrium, a forest will remove a certain amount of carbon from the atmosphere while living, and upon death return some of that carbon through decomposition. In, fact just looking at it only that way, you yourself ( and it can be said of any living thing ) are a short term carbon resevoir while living. You, for example, have certainly more carbon within you body now than when you were a small baby. But the carbon cycle is much more complicated than that.

    But, getting back to trees. forests, and how plants and their influence become a major carbon sink.
    the bigger picture is what is important here for climate models regarding the carnon cycle.

    It really is not the biomass of the living, but the storage of the dead.
    The forest soil is actually where the carbon sink is in the long term.
    If the forest ceases to exist, the carbon within will have a good chance of being returned to the atmosphere as carbon dioxide.

    For a preliminary, please read:
    https://en.wikipedia.org/wiki/Mycorrhizal_fungi_and_soil_carbon_storage

    https://en.wikipedia.org/wiki/Soil_carbon

    As you can see from above, the soil carbon vastly surpasses the biomass carbon and atmospheric carbon.
     
    Last edited by a moderator: May 7, 2017
  9. Sep 11, 2015 #8

    jim mcnamara

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    Plants are a kind of living carbon sink. Wood and xylem is primarily sugar polymers: lignin and cellulose, which are only reversible via a few organisms, and this does not happen in living tree tissues. PS: Sugars have a lot of carbon in them.

    So if a tree is 100 years old it is usually large with lots of wood. If it accreted rings of growth for 100 years - the innermost wood ring is made from carbon dioxide that was converted into sugar 100 years ago. The carbon has been locked in there for that long. Bristlecone pine trees can live for literally thousands of years. See: https://en.wikipedia.org/wiki/Bristlecone_pine

    That means in a very simplistic way that the idea of fungal respiration (giving off carbon dioxide) reversing all of photosynthesis right away in living trees or plants cannot possibly be correct. Plus fungi often undergo anaerobic respiration - turning sugars into complex organic molecules. Those exudates become bound into soils by leaching the molecules away from growing roots. So the carbon is "parked" out of immediate reach.

    Also in bogs and swamps, trees that deadfall often end up preserved in sphagnum moss exudates for loooong periods. Check out bog oak pictures:
    http://mtss-woodblog.blogspot.com/2013/02/celtic-irish-bog-oak.html
     
  10. Sep 11, 2015 #9

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  11. Sep 11, 2015 #10

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