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The tree would drown.
Trees require evaporation through the leaves to draw nutrient enriched water from the roots through the trunk to the leaves. Which then evaporates and causes the process to be continued. They also require Carbon for the photosynthesis process, which trees absorb via the leaves in the form of Carbon Dioxide.Some quick diagrams
Source: https://www.evolvingsciences.com/Transpiration Stream.html
Source: https://opentextbc.ca/biology/chapter/5-1-overview-of-photosynthesis/
Second one is a little simpler, but the source link is to a site with open access educational materials. Pretty cool
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)
So I know it’s not a tree, but how does algae survive underwater?
Algae can get by with dissolved gases in the water
Basically the same way, but instead of absorbing gasses through the air, it’s through the water. They don’t have stomata (air holes) that are found on plant leaves that exist on land and I believe they can absorb carbon directly through their cell walls.
It’ll die, the leaves would turn into a slushie. The trunk would keep it’s appearance underwater (logs are sometimes kept under water for processing.) And your whole aquarium would turn green from algae and mold pretty quick and you can’t look inside anymore.
The tree would die, it needs a combo of air, water, and sun to live.
Interesting sidenote to this tho, there is a hydroponic system called “kratky” where the plant roots go directly into a jar of water. As the plant grows the water level goes down, exposing more of the roots to oxygen, which is necessary for the plant to live/grow.
Your question isn’t stupid, but it does make me feel very curious about what potential hypotheses you might have been weighing.
