What would happen then if you took a tree which only has leaves at the top and submerged it to just under the leaves? Does the bark need to be exposed to air as well or would it just rot out like timber does?
Mangrove trees live submerged in saltwater for example. This video also goes over some of the adaptations it has to do that (ex. Special roots to allow it to stand upright in soft unstable ground)
What would happen then if you took a tree which only has leaves at the top and submerged it to just under the leaves? Does the bark need to be exposed to air as well or would it just rot out like timber does?
It would die. The roots need to do gas exchange too. Ideal soil composition is generally 45% mineral, ~25% water, ~25% air, and 5% organic matter.
Tree bark also does gas exchange.
Depends on the tree and type of water I assume
https://youtube.com/watch?v=twjPo2Luk5A
Mangrove trees live submerged in saltwater for example. This video also goes over some of the adaptations it has to do that (ex. Special roots to allow it to stand upright in soft unstable ground)