Does H2O readily give up a hydrogen for plant uptake, or does it require an acid such as carbonic or chlorophyll to help release that hydrogen for plant use?
Plants use light energy to split water.... it is part of the photosynthesis process, specifically the light-dependent reaction (photosynthesis is a 2 stage process). That same reaction that splits water also captures energy by converting ADP to ATP. The second reaction then uses the hydrogen ions, CO2, and energy from the ATP being converted back to ADP, to form sugar.
Remember, photosynthesis works by taking light energy, and using it to convert simple oxides (H2O and CO2) back into hydrocarbons (glucose sugar).. Those hydrocarbons can later have their energy released by re-oxidizing them back into H2O and CO2.
I am sure CO2 is helpful in plant growth. What I am wondering is by what means is CO2 helpful. :}
CO2 is used to provide the carbon needed to form the backbone of sugars..
Earlier I stated the overall input/output of photosynthesis:
6 CO2 + 6 H2O + energy (sunlight) -> C6H12O6 + 6O2
That simplifies the overall process, as there's actually 2 complex reactions going on and several intermediary compounds used (chlorophyll, ADP/ATP, etc), but the intermediaries aren't consumed and just get used over and over again...
Regardless, you an see the glucose molecule, which is food energy in the form of sugar, is C6H12O6... You can't make this molecule without carbon.. It is absolutely critical to the plant to manufacture its own food and store it..
Some of those sugars never get burned by the plant as energy, and instead get bonded together to form cellulose, which is the "fiber" that makes up the physical structure of the plant.
Plants, like animals, are fundamentally a hydrocarbon based life form. Carbon is *very* important to all living things on earth. All sugars, starches, "dietary fibers" and fats are fundamentally just chains or rings of carbon atoms with hydrogen and oxygen hanging off them in different ways.