Air & Light On Leaf Photosynthesis:
As a leaf ages, its ability to photosynthesize follows almost like a bell curve, with a peak around 20-60 days. Here it can be seen how leaf age is very impacting on its photosynthetic capacity. As the leaf gets older, aging or senescence brings about deactivation of enzymes and degeneration of chlorophyll. This is why older leaves start dying and fall off on the lower end of the plant.
It has been suggested that older leaves may act like sinks when they can no longer continue to efficiently convert light into food. But this is not what happens. In the early stages of leaf development, leaves act like sinks. In just a few days, leaves begin the Sink To Source transition where they start supporting themselves and begin exporting photosynthetic resources, as a source. Its at this point and for the remainder of its life until cessation that it stays as a source. Removing leaves does not provide more photosynthate for flowers, as leaves are providing energy, not requiring it. They are sources. The plant also utilizes the nutrients and energy leftover from the leaf, prior to abscission during senescence. This is what happens during the late stages of flowering when the plant is searching for nutrients.
One could argue that reducing foliage will help prevent leaves from the top, from blocking light and reaching lower into the canopy, however this is only going to end up with the same 'total' photosynthetic yield. All that is changed is where the photons will land. Any light which is not absorbed from higher leaves will pass through to lower leaves. This is called the transmittance effect. The idea that top leaves block lower leaves and waste usable energy, is incorrect for this very reason. As light is captured efficiently. Infact exposing shade leaves could be harmful because of the shade vs sun leaves problem. Shade leaves have a different anatomical structure compared to sun leaves, as such its capacity to process light is limited and is negatively affected through factors such as photoprotection and photoinhibition. It takes time for leaves to adapt to new lighting environments. Removing sun leaves and exposing shade leaves, could slow growth and add time to the overall schedule. This is the reason why plants have problems when being introduced into new lighting environments.
With airflow and transpiration, the process is completely passive. But we can prevent problems such as water vapor barriers from static air, sufficiently with active air movement. By removing leaves, you ultimately limit the plants ability to move water and nutrients through transpiration, as the leaves that are removed contribute to this through stomatal movement. By removing leaves you prevent the plant from breathing so to speak, as such the plant tries to recover and attempts to generate more leaves as a result.
