The vast majority of a tree\'s carbon comes from the air, which averages 0.03-0.
ID: 30752 • Letter: T
Question
The vast majority of a tree's carbon comes from the air, which averages 0.03-0.04% by volume (300-400 ppmv) CO2. This is fixed through photosynthesis and eventually stored as glucose which the plant can then use for its metabolism.
Doing some quick math, this means that in order to produce 1 kilogram of carbohydrates (e.g. cellulose) a plant needs to process on the order of 2000-3000 cubic meters of air (and ?550 g or mL of H2O), which would fill a cube measuring 13-14 meters on a side. Note this is an ideal figure; a plant's fixing efficiency will likely fall as it depletes the air of CO2.
Plants do take a great deal from the ground, namely water, fixed nitrogen (for proteins), phosphorous (for nucleic acids), and several ions (sodium, potassium, calcium, among others)
Explanation / Answer
I'm surprised nobody has mentioned Jan van Helmont. To summarise Blankenship's account, in the 17th century, he (Helmont, not Blankenship) grew a tree in a known dry weight of soil and weighed the fallen leaves of the tree, and then eventually the whole tree including the root system. He found that the mass of the soil had barely diminished and concluded that the tree's mass was overwhelmingly due to watering (CO2 had not been discovered.)1
With the benefit of knowledge of CO2 we can conclude that the mass of trees comes from the fixation of CO2 and H2O as well as the presence of H2O as a biological solvent.
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