Given an apparent solar brightness of <30% Sol from Earth, how differently would plants evolve?

Though my star is 1.71 L_Sol, my planet orbits at about 2.14 AU. Following a back-of-the-envelope equation for apparent brightness, this gives the surface of my planet approximately 30% of Sol's light energy. It would actually be substantially less; my planet is extremely geologically and volcanically active, so I would expect a high concentration of reflective volcanic particulates to be a semi-permanent fixture in the upper atmosphere. It also has a high obliquity of 31.1 degrees, and 93% of its surface is ocean; as such, hurricanes are very common and very powerful. My atmosphere is quite thick and rich in carbon dioxide: 16% CO₂ in a 134.76 kPa atmosphere.

My question is:

How would plants evolve differently to more efficiently capture the light energy coming to the surface, yet survive the constant hurricanes (or at least reproduce quickly enough that the hurricanes would be a non-issue)? My working theory is that the plants could only survive with a much more balanced and diverse range of photosynthetic pigments; and/or plants would barely survive at all, and the flora of my world would mostly be made up of oceanic blue-green algae.

Keep in mind that increasing the surface area of the leaves would only work in very specific regions of my planet's land masses; these plants also need to worry about conserving temperature (a BOTE calculation puts my planet's average temperature around 10-15 degrees C) and water (the only areas sheltered enough from the constant hurricane and also warm enough to sustain large-leafed plant life are high-altitude deserts on my planet).

Here's what I have so far:

So I was thinking mostly coniferous needle-leafed plants with a blue-green photosynthetic pigment balance like phycobilin and chlorophyll in most "temperate" climates, and/or a carotinid-based plant phylum that evolved separately in an isolated region to the northwest. (Since 93% of its surface is ocean, and since it's so geologically active, my planet has plausible continents that have separate evolutionary timelines.)

Please let me know if you think I'm on the right track; I am NOT a biologist or botanist by any stretch of the imagination!

EDIT TO ADD:

I have been informed that my concerns about temperature regulation are largely unfounded, which is a good reminder that I need to thoroughly check my assumptions about what exactly would be different from Earth. Here is a very helpful reply I got from u/Cruzzfish on the r/worldbuilding subreddit!

"They really wouldn't be that different at all. Many plants already require lower than 30% of the sun's full brightness if they don't want to sunburn. Even full sun plants don't have too much of an issue operating at <10% of the sun's brightness for extremely extended periods of time.

Notable differences would be.

More salt tolerant wetland plants to take the storm surges

Less brightly colored ones since no need of sun protective pigments.

I don't know what you mean by conserving temperature. Plants don't need to worry about that sort of thing. But a planet with an average temperature of 15 Celsius is not cold at all. Earth average temperature is just over 13 Celsius..."

"...Seaside goldenrod is decently salt tolerant but I don't know how it reacts to floods. Generally there are a lot of seaside ____ plants that would be good to look for."

And from u/svarogteuse:

"They would evolve just like plants on the Gulf Coast/Caribbean; they drop small leaves freely but regrow them quickly.

About 2 years after Katrina I went to Bay St. Louis, the place it actually came ashore. Along the beach was a brand new road recently rebuilt. To the left the remains of a boardwalk and sand. To the right beautiful park land for about 6 blocks with huge live oak trees. The live oaks looked a little funny. Took a few days to figure it out. The trees had limbs bigger than my torso and twigs with leaves. Nothing in between. Every thing smaller had been ripped off by the hurricane.

Oh and the park land wasn't parkland. It had been full of houses and now the only thing left was foundations. Everything else had been carried off by the 25' storm surge. Storm surge the 200 year old oaks (but no smaller ones) withstood."

posted about 6 years ago

Rúnatál Davino‭

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