In article ,
P van Rijckevorsel wrote:
One tomato will require a fixed amount of nitrogen, irrespective of the
speed at which it grows. If a plant produces two tomatos where before it
produced only one it will require more nitrogen.
For many plants the limiting factor is water. If photosynthesis is twice as
efficient, likely a plant will grow twice as fast.

Yeah, and if they have enough water, the limiting factor is often CO2.
It's economically worthwhile to crank up the CO2 level in greenhouses
when growing lettuce and "Dutch aquarium" fanatics add CO2 to the water
to get that incredibly lush growth of aquatic plants.

Only when the plant gets the most it can use in the way of water, mineral
nutrients, light and CO2 is it going to run into the intrinsic limits to
photosynthesis and growth. Using genetic engineering to increase food
production is better directed to develop plants that will grow well under
worse conditions. A few years ago a collaborative project between the
U of Toronto and UC Davis moved some Arabidopsis genes for salt tolerance
into tomatoes. With all the soils in the world that have been degraded
by mineral salts from fertilizer overuse and irrigation, salt tolerance
may be one of the most valuable traits that can be engineered into crops.