Photosynthesis is driver

​Photosynthesis is the engine driving corn from the seedling to maturity.  Previous generation's photosynthesis provided the energy for the seedling to emerge from the soil. Current generation photosynthesis provides more than sufficient energy for the metabolism to build tissue to construct a plant with expansive roots, large leaves, and 6-9 feet of stalk within a few months of seedling emergence.  The corn plant not only provides the energy for the building materials for its new structures and daily metabolism but also has excess carbohydrates that are stored in the stalk pith cells.
 
Then, at midseason, it produces flowers.  After pollination for the female flowers, hormones in the plant shifts the direction of flow of the carbohydrates from leaves and stalk pith cells to the the new embryos and its storage compartment, the endosperm.  Environment and genetics determine the rate of flow of carbohydrates to the new fruit of the corn plant.  The number of fruits (kernels) also becomes a big influence on the total draw from the carbohydrate supply.
 
Flow for first 10 days after pollination is relatively slow but then it speeds to a faster, relentless pace for the next 40 days.  That daily pace of movement of carbs to the ear on the plant continues regardless of daily variation in photosynthetic rates due to environmental variables.  If cloudy weather slows photosynthesis, the reserves in the stalk provide the difference.  If leave disease reduces leaf area available to light energy conversion to carbohydrates, storage from early days is called upon for movement to the new kernels.
 
This high rate of flow of carbs to the new kernels slows after day 50 for about 10 days until it is cut off with the formation of an abscission layer at the base of each kernel.  If the other plant parts such as the root tissue survived the competition for stored carbohydrates in the stalk, slow senescence occurs in the plant cells. This is the outcome desired by all corn growers but environmental stresses can interfere with the completion of maximum deposit of carbs in the kernel on living plants.