Hacker News Reader

Comment by jessriedel | Hacker News Reader

Does anyone know what the evolutionary bottlenecks/tradeoffs are for more efficient photosynthesis?

It is a very very old protein, stuck in local maximum more than anything else.

I suspect there might well be an evolutionarily balanced tradeoff between "construction cost" and "lifetime energy output" of a plant's photosynthesis machinery - as well as a likely overabundance of available solar energy in terms of what a plant actually can use. (Why build a potentially more complex and fragile photosynthesis pathway that's 50% more efficient, if you can instead just grow twice as much leaf surface area?)

But there are places where plants compete fiercely for small amounts of sunlight, such as in forests (especially tropical rainforests). Doesn't your theory suggest they'd use more efficient systems there?

Don't forget plants get the energy back from making a leaf in a few weeks. Solar panels take considerably longer. Generally plants are optimized to compete with others in their niche and as such it's exponential growth that's most important not total energy capture.

https://en.wikipedia.org/wiki/C4_carbon_fixation

Example of such an evolutionary step. C4 vs C3 photosynthesis.

C4 is more efficient in water usage, but less efficient than C3 in energy production

Is it actually tropical rainforests, or temperate, that limit sunlight most? Old-growth PNW forests often have large patches of western hemlocks that produce so much shade that no other tree can grow under it, not even conifers - and unless there's a fire to clear some space out, it can stay that way for centuries.

> stuck in local maximum more than anything else

What's the argument that this is true, rather than it being better than more efficient proteins on some other metric?

Plants in arid environments have evolved a more efficient carbon fixation process -- https://en.wikipedia.org/wiki/C4_carbon_fixation -- in response to decreased water in the environment.

Despite this, C3 plants still dominate the planet, so somehow selection pressure hasn't shifted strongly towards C4 plants in non-arid environments.

According to the wikipedia page, C4 is more efficient in water usage, but less efficient than C3 in energy production.

https://en.wikipedia.org/wiki/C4_carbon_fixation

Oh makes sense. I somehow read over that sentence.

Selection pressure may well have shifted towards C4 in the future if we hadn't come along and been kind enough to dig up some fossilized carbon and put it back into circulation.

I don't know but my guess is to have more efficient collection/processing may require bigger leaves which may be too heavy or catch more wind damaging branches.

Or maybe trees are just lazy by nature?

Reply on news.ycombinator.com