Dried plants are 44% carbon with all of it coming from air. There is no carbon dioxide in ground water unless considerable humus or limestone is present.  And, in the latter case the water needs to have a low pH or be exposed to sunlight with the water. These are all exceptional cases. With only 0.038% carbon dioxide in the air; green plants must process 1,157 pounds of air, or 18,512 cubic feet, to make every pound of sugar, starch, cellulose or wood. 

           Carbon dioxide enters plants through small leaf valves called stomata, tiny donut-shaped valves guarding tiny alveoli-like (lung cell) leaf organs where CO2 diffuses into the plant’s circulatory system.  However, we have shown carbon dioxide may be better absorbed through roots where CO2 has been added to soil moisture.

          Stomata have been compared to our pores and sweat glands, but their function is not that of controlling temperature.  We conclude this from the fact that cacti and bromeliads have so few stomata and they are hot climate plants.  Green plants deal with high temperatures differently from animals, a fact long overlooked by science.  

          Given the differences in the solublities of nitrogen and oxygen compared to CO2 we see the stomata as a carbon acquisition port entirely and one powered by the evaporation of water. How it works is not fully understood, but a lot more water vapor goes out than CO2 comes in suggesting a swap of some kind.  It may be that in order to maintain permeability for incoming CO2 excess water must be lost.  

        We see stomata close when we supply CO2 through the roots.  The system of acquiring carbon from the atmosphere is grossly inefficient and we improve it greatly by putting CO2 in the soil's moisture..  In empirical tests we reduced transpiration 20% in small pots where water was also lost from open soil and the 20% reduction was very likely an underestimation of the effect.  Nonetheless there were spikes in the performance ranging to 30%, but a definitive experiment needs to be done.

      Cactus is the key to large water savings when we supply CO2 from the earth as cacti have very few and small stomata.  When we find the genetic code determining the number and size of stomata in grain plants and substitute the cactus code we will have a plant that will use substantially less water. It will rely on our supplying carbon dioxide from the earth.  Such plants will not be able to escape cultivation and affect the wild environment.  They will strangle in one generation of not being fed with underground CO2.  The concept that most transpired water is used by plants in exchange for air to capture carbon dioxide is new and guides our work.

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