The "tricky" answer to the question of where most of the mass of wood comes from is "from the air". But does it?
Most of "wood" - the hard substance everyone is familiar with is made of cellulose and other hydrocarbons. Looking at what cellulose is made of, it's easy to see it's predictably, made of C, H and O atoms. It's a chain of glucose mollecules and its basic formula is C6H12O6, in which O is the heaviest atom (16) followed by C (12) and H (1). Lignin, the other major substance, is more complex - it's actually a mixture of several similar substances and it constitutes "a quarter to a third of the dry mass of wood".
Now I have two questions:
- From where does the oxygen come from? There's a lot of hydrogen around, (in quantity, not weight) and I suppose it comes from water (which is sucked from ground), so how much oxygen also comes from water? There's more oxygen in CO2 than in H2O but then the plants also exhale a lot of it.
- Is the amount of carbon-dominated (by weight) lignin enough for it to outweight the amount of oxygen-dominated cellulose?
This is just a bored-geek analisys, I don't claim it's very accurate, but it doesn't seem too far fetched that the given, supposedly tricky answer, might be wrong.
Any chemists or biologists around?
(In any case, the TED talk is worth seeing)
#1 Re: Where *does* the mass of the tree come from?
The roots take in oxygen (as in they breathe - ie why they need a wet/dry cycle) and other required nutrients, mainly Nitrogen, Phosphor and Potassium (N-P-K ratings u see on fertilisers) - in recent years we have discovered that there is a relationship with other microbes and fungus in the soil which help break down the fertilisers/nutrients to a form which the chemicals are more available for a plant to absorb - there are some fungus which actually attach to the roots and have a fully symbiotic relationship with the plant.
If the soil/compost is over watered anaerobic organisms take over and the plant will die as these will essentially poison the air supply to the roots (as well as them being drowned).
But essentually most of the mass of the plant is from the carbon it takes in from the CO2.
#2 Re: Where *does* the mass of the tree come from?
I'm not a botanist, but I do recall that increased CO2 levels will greatly increase the speed with which any plant grows. This would support the "air" theory.
#3 Re: Where *does* the mass of the tree come from?
From photosynthesis ( http://en.wikipedia.org/wiki/Photosynthesis ) and water I guess.
The question 'Where does the mass off the tree come from?' might be the same question Lavoisier ( http://en.wikipedia.org/wiki/Lavoisier ) had in is had while disproving phlogiston theory ( http://en.wikipedia.org/wiki/Phlogiston ) ;-)
#4 Re: Where *does* the mass of the tree come from?
The oxygen molecules released by plants (or the two oxygen atoms in them) are surprisingly always taken from the H2O molecules they draw up, not from the CO2 molecules they absorb! (The CO2 is used in the Calvin cycle to make sugars) And it is definitely correct that the majority of the biomass of a plant (its dehydrated mass) is composed of compounds from the air! Strange to think that a giant redwood is in a sense mostly air! What continually happened that got me searching for these answers was bumper to bumper traffic. You always see these weeds growing on the freeways in the tiniest cracks. There can't be much soil in them or other macro-nutrients, yet these weeds have quite a bit of mass, so where does it come from? Well the only other available substances to build with are water (which is sparse in california) and of course air. On an aside, the freeways supply a copious amount of CO2 for a plant like this.
#5 Re: Where *does* the mass of the tree come from?
Though the carbon in trees clearly comes from the air, the dry wood of trees is slightly less than 50% carbon (http://www.woodenergy.ie/iopen24/defaultarticle.php?cArticlePath=5_31 ). This is reasonable, given that cellulose has almost as many oxygen atoms as carbon atoms. Does the oxygen come from the CO2 or H20? This link cites the experiment that showed that ALL the oxygen gas given off by the plant comes from the H2O. If you count the atoms in the photosynthesis reaction, ALL the oxygen in the carbohydrate will be from the CO2. Thus the vast majority of the mass of a tree (dry) comes from the air.
#6 Re: Where *does* the mass of the tree come from?
here is the link that I negelected to inlcude in my previous post: http://bcs.whfreeman.com/thelifewire/content/chp08/0802001.html