Back when I was young and keen, I was a biology major. I don't remember a whole lot from my botany course (it has been 45 years). I did remember a few things, and a quick internet search confirmed my memory.
There are four types of photosynthesis that plants utilize: C3, C4, intermediate C3-C4, and CAM. By far the majority of plants on Earth are C3 plants--upwards of 80%. The Calvin Cycle is what this process is called. When temperatures get too hot and dry, C3 plants fold up shop and efficiency suffers due to photorespiration. Almost all our food and fiber consumed on Earth are C3 plants.
C4 plants are uncommon, with <1% of all plants utilize C4. (Sugarcane and corn are among them). This method undergoes a two-step process whereby the initial process forms a four-carbon molecule (malic acid) before an additional step changes it to a 3-carbon molecule to continue photosynthesis like a C3 plant. C4 is much more efficient that C4, and does not suffer nearly as much during hot and dry conditions.
I don't recall anything about the intermediate C3/C4 types of plants and their processes of photosynthesis.
CAM plants (about 10%) are unusual in that they are primarily in desert areas where the days are hot and dry and water is scarce. These plants are mostly cacti, succulents, and other denizens of the desert. The stomata on CAM plants open at night when it has cooled off and absorb CO2. During the night, the plant converts CO2 to malic acid for storage. The stomata close when it warms up the following morning and then utilizes the stored malic acid for photosynthesis like C4 plants.
My feeling is that plants have adapted to certain levels of CO2 in the atmosphere that have remained within certain parameters for millennia. We really do not know if significant increases in ground-level CO2 would have potential deleterious effects on the efficacy of the plant's life cycle. For example, would increases in CO2 require more water? Would the plant need to take up more nutrients from the soil? Would the yields -- food, fiber, and timber -- be less? Would there be increased stress on the plant by insects and air or soil-borne pathogens?
I am not suggesting that what I wrote is relevant to climate change and global warming. But I submit that these effects on all the plants that undergo photosynthesis have not been adequately addressed by those who are arguing either side of climate change and global warming.
