A large oak tree has about half a million leaves. After they drop in winter, the tree has from April to july to make another half a million leaves. All it uses are dissolved nutrients from the earth and sunlight. Now half a million leaves is a heck of lot of matter to create. How do they manage to make so much cellulose etc. Just out of water and dissolved minerals. :smack:
The bulk of a plant is made from the carbon dioxide in the air, via sugars assembled in photosynthesis.
Otherwise known as “why we respirate.” 
Huh? I think you have it backwards. Respiration is a CO[sub]2[/sub]-producing process. Photosynthesis consumes CO[sub]2[/sub]. Plants do both.
Photosynthesis has two distinct components, broadly named the light and dark reactions. The light reaction captures solar energy and results in net ATP, NADPH, and oxygen production. ATP and NADPH is used in the dark reaction, which is responsible for assembling glucose from water and CO[sub]2[/sub]. The glucose is both used in respiration and other biosynthesis, such as cellulose production.
I think you have been “wooshed”… I think the comment was a bit of a twist on the idea that plants are there to make oxygen for us…The comic idea is that its the other way around and we are slaves of plants.
How much of the Nitrogen in the leaves decompose and re-enter the soil … to be taken up again by the tree? Is there some manner of cycle here?
Yup.
The BBC broadcasted an amazing four part series on the life cycle of a 400 year old oak tree - “Oak Tree: Nature’s Greatest Survivor”
I can watch it on iplayer but I think that is not possible in the USA. Maybe there is another way to see it because it would be well worth the effort.
Gee, did anyone ever think that plants existed* for the benefit of animals*?
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Should this be “respire?”
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Cf. Economic/economical?
Can a net energy expenditure (per season) of the nitrogen cycle for one large oak tree to “leaf” (what’s the word equivalent "to flower?) be given in joules?
The energy expended in the organism.
Perhaps in addition to the photosynthetic processes to “make” all those leaves, the chemical energy necessary for the intra-organism mechanical processes (the upwards and outwards of, at the largest image, the sap) can also be theoretically isolated.
ETA: It’s funny this is on my mind again, I now see–good pointers were given in I may be a diabetic, but I’m not adiabatic: what is exothermic at any one moment in my metabolism?, http://boards.straightdope.com/sdmb/showthread.php?p=19694736, with specific reference to the human organism. Maybe some plant bio people have a different take.
(Groucho Marx–“Why don’t you drill a hole in your head and let the sap run out.” To save the trouble if this query prompts a similar thought…)
Yes. Whoever wrote Genesis chapter 1, verses 29 and 30.
(And I’m sure you can come up with similar examples from other religions.)
So is there any other living organism that can create so much matter in a matter of months. Apart from other large trees.
It depends on how you look at it. There are algal blooms where tons of biomass is created…but do you count the asexually reproducing algal cells as one organism, or billions of organisms?
Baby blue whales grow about 90 kilograms every day when they’re nursing. That’s a lot of milk. Something like 200 liters every day. Whale milk is higher in fat than heavy cream. So that’s a lot of biomass converted from plankton to milk to baby whale.
It really should be considered “converting” instead of “creating” matter.
With respect to other living organisms, the blue whale is one of the fastest growing animals currently existing:
Please note that deciduous trees store sugars and starches in their roots and trunk over winter, and tap that stored energy to produce new leaves in the spring. All of that stored sugar is the reason we can make syrup from Maple sap in the spring. Not all of the “matter” is new matter.
I just read an interesting book called “Lab Girl” by Hope Jahren. It is mostly about her life, but interspersed are short chapters on the life of trees that goes into these questions in some detail.
Most of the mass is just moisture though, right? Sure, a tree full of leaves seems like a lot, but once they fall off the tree and dry out, I can stick a tree’s worth of 'em into a well functioning compost and disappear them pretty quickly. I’m always amazed at the volume of leaves I can add and after they’ve disappeared the level of compost really has barely gone up noticeably.