See that white tree there amongst the green ones? I'm not certain, but I think it's an albino.
Like animals, some tress are born as albinos, devoid of pigments due to a genetic mutation. Without photosynthetic pigments, a tree cannot harvest energy from sunlight and normally wouldn't survive. But in a rainforest, any tree will be nurtured by the rest of its community, sharing resources through their roots. Even a tree unable to give anything back.
Image credit: Paulo Whitaker/Reuters
In North America, albino redwood trees are quite well known. Unable to support themselves, they survive purely through the help of the other trees which surround them. In a forest, those with more always give to those with less, so that all can survive.
That's an example for all of us to learn from.
Sounds cool, so how does that work?
Forest trees are interconnected by vast networks of fungi – Mycorrhizal networks. Anything connected to the network takes what it needs from others and gives back any surplus it has. That way, the forest works together for mutual benefit.
So what does this tree need it can't do on it's own?
(I also liked the analogy btw, but more interested in the actual biology :)
Oh, that was no analogy. That's literally what happens.
Being completely without chlorophyll, an albino tree can't photosynthesise and therefore can't produce sugars. Most of a plant's living structures are made from sugars – mostly cellulose and lignin.
The large trees in a forest produce more than they need. They share it through their roots in a process called rhizodeposition. Fungi in the soil pick up those sugars, take what they need, and share the rest with other trees. That way, there will always be healthy trees providing more sugars.
Meanwhile, the fungi break down decaying matter and harvest nitrogen from the soil, again passing on any excess to the trees.
Everything nurtures everything else. By helping other organisms to survive, they ensure that there will always be someone helping their own survival too.
@webmind @Nocta @InvaderXan BTW I dug a little deeper and it turns out that albino redwoods need a root-graft connection for sap exchange, so the mycorrhizal network isn't involved — understandably, since fungi are unlikely to give away sugars they can use to build their own empires. Also, there's a new paper about how maybe they concentrate toxic heavy metals so other trees don't have to suffer them
@InvaderXan @webmind @Nocta This paper is great, thanks! But it doesn't actually say the carbon they transport is in the form of sugars; the only time it mentions carbohydrates at all is when it's talking about root grafts like the ones I said sustain albino redwoods. What leads you to believe that the carbon transport they detected is in the form of sugars rather than, say, carbonate?
@InvaderXan @webmind @Nocta Fungi aren't plants; they metabolize sugars into water and carbon dioxide, or, more generally speaking, carbonate — there's a dynamic pH-dependent equilibrium between carbon dioxide, carbonic acid, and carbonate ions in aqueous solution. (Plants do too in their respiratory processes.) It would be far less surprising for mycorrhizal transport of carbon to consist of sugar that is then oxidized within the fungus.
@InvaderXan @webmind @Nocta The reason this matters is that carbon atoms in carbonate are already fully oxidized and don't provide energy to the plants that take them up; they provide mass that can be incorporated into sugars by photosynthesis, although of course the albino trees couldn't do that.
You're correct that carbonate forms salts with very low solubility with certain cations, such as calcium, but other carbonate salts are highly soluble; think about your blood.
You're once again trying really hard, but you haven't provided anything beyond your own conjecture and supposition.
I've already proven you wrong about rhizospheric carbon transport. You're still attempting to refute me, for some reason. The burden of proof is on you. Until you provide any, I'm not continuing this.
@InvaderXan On the contrary — I already knew about mycorrhizal carbon transport, and never intended to deny its existence or importance, although the paper you found demonstrates that it's far more extensive than was previously suspected. My contention is with your apparently novel suggestion that commensal fungi provide trees not merely with *carbon* but with *sugar*, which the paper does not even suggest, contrary to your assertion.
@InvaderXan So you've — apparently unknowingly — proposed a hypothesis that's entirely outside of the scientific mainstream, and now you're claiming that the burden of proof is on me to find evidence against it, because you previously misinterpreted me as rejecting the well-known nutrient-transport role of commensal mycosymbionts.
It's true that I'm making a great effort here. I hope it is of some service to you.
The exact same can be said of your carbonate hypothesis. Still waiting for you to provide more than just conjecture. You’re not making much effort on that.
@InvaderXan Oh, I didn't mean to suggest that carbonate was the only plausible non-sugar molecule for aqueous carbon transport from hyphae into roots; it's just an example, the first one that came to mind, since the carbonate/bicarbonate/carbonic-acid buffer system is the immediate result of aerobic carbohydrate catabolism. But there are lots of water-soluble carbon-bearing molecules that aren't sugars!
Net carbon transfer is observed between interconnected plants (Simard et al, 1997). Carbohydrates (typically monosaccharides like hexose) and lipids are the main candidates for the form of carbon transferred through mycorrhizal mycelia (Bago et al, 2000). And arguing over specific organic molecules does not contradict my original points.
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