Another Giant Tree Attempt

Question

I want to propose a new method for tree growth to exceed the max of 120 or 130 meters restricted by Earth's gravity. I propose for the tree to rely very little on its base or roots. The living part of the tree really only encompasses the top 100 meters of the tree and some its bark. The trees are are hollow with a foam like inside that incorporates metals from the soil to strengthen its tissues. I would like to know what metal or minerals from the soil it would need to incorporate into its tissues as it grows.

General Biology:

• Gathers most water and nutrients from the canopy ecosystem
• Found in environments with frequent rain but not harsh storms or hurricanes
• Lifespan of thousands of years
• Live on an Earth analog planet (same gravity, etc.)
• Live on a planet with non-toxic metals abundant in surface soils (platinum, tungsten, titanium)

Edit: The tree uses a U-shapes tube that is along the side of the tree going from the bottom all the way to the top 100 meters of the tree. The tree excretes metals and minerals into the tube at the bottom and then water is flooded into the tube by the tree from the top, allowing minerals to be distributed into the tissues higher up in the canopy as the tube is flooded.

Question: How much could the tree increase its height after incorporating minerals into the non-living foam or web like tissues of the tree?

Answer 1

If the tree were to use this method, getting minerals from the ground, but water from rain, the obvious problem is the amount of rain. If the tree is very high, it needs more area to catch rain or thinner tubes to carry the nutrients up. So it needs to span a larger area, which shades the soil more, which affects the minerals therein. This should be taken into account.
Next, there is the thought of seeds. This tree would very tall, but would also need to reproduce. If only the top 100m were alive, this would be where the seeds are created. If they were to fall from very high, they would reach speeds closer to their terminal velocity. Thus these seeds need to be designed to survive this.
Aside from velocity, another thing needs to be accounted for at high altitudes: Temperature. If these trees were to grow to superterrestrial heights, they would be exposed to greater cold, which would also need to be kept in mind when designing seeds. This also complicates the "water tubes" theory, or at least sets a limit to the height, as water freezes at subzero temperatures and minerals saturate the water more quickly.
In conclusion, I would say it is possible, though difficult to make a model for. An upper cap for the size would be freezing altitude.

Answer 2

The availability of metals is unlikely to be the deciding factor, water supply by capillary action to the top of the tree is the limiting factor for the tallest trees on Earth. If your tree relies on collecting rain water instead then this problem might be resolved, however it would need to rain a lot and dry spells could be deadly.

But another issue would be the ability of the upper levels of the tree to receive sufficient minerals since it would not be able to absorb such nutrients from the soil as only the top 100m of tree is alive and only the very smallest amounts would be present in the rain. As the highest structure (presumably) in the forest very little could fall into it.

So I suggest that 100m would be the effective maximum size of your trees. In extreme cases trees on Earth can grow to 115m.

Note Platinum, Tungsten and Titanium are unlikely to be metabolised by a tree due to their chemical reactivity or lack thereof.

Answer 3

Trees grow out of the air

Contrary to expectations trees don't grow out of the ground, they grow out of the air. The vast bulk of a tree's mass is carbon, extracted from carbon dioxide. The limiting factor on height is the mechanism they use to draw water up from the ground.

The model you've chosen, of most of the tree being dead mass and only the top 100m or so of the tree being live, is not impossible as long as you find a new source of water and nutrients that doesn't require access to the soil. Since you have allowed for that, your limiting factor is now the compressive strength of your petrified tree trunk. There's no limit to how much mass your tree can draw out of the air, there is a limit to how much mass its structure can support.