Wheat harvest is fast approaching and it will be interesting to see how yields turn out after the challenges of the last nine months. There has been a test cut or two in southern Kansas with acceptable grain moistures. Today is June 10th and the last few years, weather permitting, harvest has been ramping up or in full swing.
With the weather of the past growing season, many were predicting an extremely late harvest. However, with the extremely warm August and timely rains, wheat maturity for harvest, while later than has been typical lately is close. An item passing the agriculture news briefs lately is research involving making photosynthesis more efficient and increasing yield.
While this is still a ways off from farmers’ fields, it is worth discussing, especially since photosynthesis is the basis directly and indirectly for most life on Earth. And for the botanists out there, this is a condensed version.
Briefly, photosynthesis is the process of capturing light energy and converting it into chemical energy, initially glucose. Glucose is then converted to sucrose and fructose and starch to use as an energy source and into structural components. Plants and other organisms capable of photosynthesis are autotrophs – they produce their own energy. Organisms that rely on them, like livestock and human beings are heterotrophs – we can produce our own energy.
There are two parts to photosynthesis, Photosystem I and Photosystem II. I is termed light dependent and II is temperature dependent. Photosynthesis is further divided into C3, C4, and CAM photosynthesis. Cam is typical of plants such as cacti so we won’t discuss it further.
Before explaining the differences there is one more concept to grasp – light saturation and the compensation point.
In Photosystem I, light drives how fast the light reaction proceeds where radiant energy is captured. Light saturation is the point at which photosynthesis can go no faster. Even with more sunlight, the reaction will go no faster.
The compensation point is where the rate of production of photosynthesis equals the rate of respiration. In English, it’s the rate where the production of sugar equals the amount of sugar burned by plant cells to maintain themselves. The plant cannot grow until it produces more sugar than it needs just to stay alive.
If you can increase the rate of photosynthesis, you can increase growth. And some types of plants photorespire. They burn some of the sugars produced in photosynthesis with no apparent benefit to the plant. It’s like a truck sitting with the engine on. You don’t go anywhere.
Now, what does this have to do with increasing yield? C4, like corn, sorghum and switchgrass, don’t light saturate. The more fuel, light, you give them, the faster they go. And these types of plants have little if any photorespiration.
These types of plants typically grow more aggressively and are the types of plants we see the most gain in yield from. On the other hand, many C3 plants, soybeans, wheat and other winter cereals, and potatoes for example, do light saturate.
They reach a point where increasing light has no effect on the light reaction. It can go no faster. And many of them exhibit substantial levels of photorespiration. Without going in to details, there are reasons why these differences make sense from an evolutionary standpoint.
What scientists are working on is improving the efficiency by improving light use efficiency, especially in C3 plants and to decrease the rates of photorespiration. They are finding success and it won’t be overnight but this genetic engineering should have a profound impact of food production over the coming decades.

Dr. Victor L. Martin is the agriculture instructor/coordinator for Barton Community College. He can be reached at 620-792-9207, ext. 207.