The primary limiting factor on plant growth is not generally CO2. You can know that by observing that CO2 is not really what fertilizers concern themselves with.

Water, nitrogen, and micronutrients, tend to be the big issues. Existing plants deal fairly well with around 200~250ppm CO2 because that's been the concentration for the last 20 million years.

For individual ecosystems or individual plants, yes, the limiting factor is nitrogen fixing in the soil. For the global biosphere however, the limiting factor to the creation of biomass (via photosynthesis) is carbon dioxide availability.

So is water. Trees simply do not grow if they not have water to generate new bark. We've had severe (for German standards) droughts the last few years here in Germany. All in all, the climate forecast for the upcoming years is currently: Less rain in the summer and more rain in the winter, which is also bad [1].

[1] https://www.klima-warnsignale.uni-hamburg.de/der-klimawandel...

So are dead humans

It's possible that higher CO2 levels are going to be great for some plants, however higher temperatures (with all the resulting consequences) will definitely be terrible for humans.

Shame lots of plants have been cut down in the lungs of the earth, the rainforests of South America.

I was of the understanding oceanic alge were much more responsible for oxygenation than any form flora. Not to down play the importance of trees of course.

But are they susceptible to changes in ocean temperature (either up, or down)?

The plants aren’t using it nearly fast enough or the graph wouldn’t be going up and accelerating.

Start planting trees.