Photosynthesis is not a ‘constant’
Photosynthesis does not occur at a constant rate of speed. It varies from moment to moment dependent on the availability of light, carbon dioxide, water, temperature, chlorophyll concentrations, plant nutrition and genetics. This seems obvious on the surface, yet is almost always missed during research.
We understand that limitations on water, or nitrogen, or temperature extremes can have a pronounced impact on photosynthesis and consequently on plant growth and yield.
In contrast to this ‘downside potential’ of photosynthesis limitations, there is also an ‘upside potential’.
When environment and nutrition is optimized, plants can photosynthesize much more rapidly than what is ‘common’ or ‘normal’ (depending on how you define normal).
An extreme example is tomato production in greenhouses in the Netherlands, where yields are reaching up to 100 kg per square meter, equal to 890,000 lbs per acre. (No, that is not a typo, and it does not include an accidental additional zero.) Field grown fresh market tomato yields in the US range from 30,000 to 50,000 lb per acre, or about 6% of the yields in the greenhouses. To produce those results, lighting, CO2, and nutrition are all being managed very tightly.
This perspective on managing photosynthesis is very valuable when we think about how to increase yields and crop performance, and is often overlooked.
Very importantly, photosynthetic variability is completely overlooked in carbon sequestration research.
Research reports that this or that ecosystem can sequester xx amount of carbon. Grasslands at a certain level, forests at a certain level, farmland at a certain level.
The research, and the predictions coming from that research, contain the flawed assumption that the rate of photosynthesis is a constant from season to season.
Some fields/regions will photosynthesize less and sequester less carbon than the research indicates, because of a challenged environment.
Some fields and regions have the capacity to photosynthesize and sequester carbon at rates multiples higher than the research indicates.
As photosynthesis varies, so does root exudation, carbohydrate partitioning, disease resistance, insect resistance, crop response to microbial inoculants, fertilizers, and sprays.
All research evaluating the performance of products or practices on crops should contain the parameter, “what was the rate of photosynthesis in the plants contained in the study?” When this highly variable parameter is ignored, research does not translate consistently to other fields and farms.