Hacker News Reader

Comment by murkle | Hacker News Reader

Are you sure that's measuring the right thing? Doesn't a mature forest reach a steady state where carbon in = carbon out when dead trees rot etc?

View on HN

But the carbon isn't released into the atmosphere when trees rot. Dead trees turn into soil. Most of a dead tree's carbon will be bound to the ground as soil.

Huh, I had also heard (vaguely, from somewhere!) that most of the carbon does get released back into the air on rotting.

Where does it go after the soil? The carbon that makes up a plant is definitely sourced from the air not the soil.

If the carbon was still in the soil I'd imagine fossil fuels wouldn't need to mostly come from the Carboniferous period, right?

There are two carbon cycles, the biological one (fast) and the geological one (slow). In the biological cycle carbon enters food chains through autotrophs (self-feeders, nearly all of them photosynthesising organisms like algae and plants) which capture carbon dioxide from air or bicarbonate ions from water and use them to make organic compounds such as glucose. These in turn get eaten by heterotrophs (other-feeders) such as animals who consume the organic molecules and break them down through cellular respiration where carbon in the molecules is released as carbon dioxide. Decomposers (fungi and bacteria) also release organic compounds and carbon dioxide when they break down dead organisms and waste products. Rinse, repeat.

The fungi that grow on dead trees perform cellular respiration, which releases CO2 (sugar + O2 -> CO2 + water + energy).

I am not sure that is true. There has been some change in opinion on whether old growth continues to be a carbon sink. I don't have a good ref handy, but found this:

"Until recently it was believed only young forests sequestered atmospheric carbon in early growth and that old-growth forests were only sinks in which the carbon was stored. Recent studies, however, have identified that intact old-growth forests continue to take up carbon from the atmosphere even past the point at which they reach maturity. By measuring growth rates, researchers have identified that carbon sequestration in trees increases continuously because the overall leaf area increases as they grow, enabling bigger trees to absorb more carbon from the atmosphere. Older, larger deciduous trees reproduce more new leaves, thus capturing the most carbon from the atmosphere."

http://www.futuredirections.org.au/publication/role-old-grow...

Reply on news.ycombinator.com