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re: How deep will plants grow?

David Marshburn said :
"The maximum depth for freshwater angiosperms is 10-12m, or
2 atm of
total pressure, or 1 atm of hydrostatic pressure"

Mosses and algaes don't have the internal air-transport
of vascular plants, and so can better deal with the greater

Also, marine angiosperms are adapted to depths of 30m. "

The last part is really interesting. How are marine
angiosperms more able to withstand greater depths? Sea water
being more dense would also be app. 1.025 times heavier than
fresh water. What allows Posidonia for example to withstand
pressures at depths more than 30m? I've seen references that
state the maximum depth for P.oceanica is the compensation
depth (ie photosynthesis = respiration) which implies that
it is the light penetration which is the limiting factor.
Has it lost the air transport system of its terretrial
ancestors, (like deep sea fish do not have a functional
airbladder)  or has it evolved a new mechanism to overcome
the pressure?



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