Photosynthesis, Maximized
input than a sparsely planted one and plants’ requirements for light tend to change from seedling through to
maturity. Ideally, all the plants in the growing area should
receive sufficient light to allow them to reach a point
termed ‘light saturation’—that is, the point when further
amounts of light don’t provide any additional increase in
photosynthesis. However, what usually occurs is that most
of the plants will remain at a point below the light saturation level, as leaves and plants end up shading each other
as they grow and develop.
Not enough and
too much light for
photosynthesis
High density and over crowding of plants lowers light penetration and overall
plant photosynthesis.
A common situation in indoor gardens is insufficient light for
photosynthesis. This is often because too many plants end up
crammed into a small space—plant hoarding is, after all, pretty
common with gardening enthusiasts—or because small plants
have rapidly become large mature ones, filling the available
area with dense foliage. In this type of situation photosynthesis
is limited by light availability and if the situation is severe the
crop might even fall so far below the light saturation point that
it reaches what is termed the ‘light compensation point.’ This is
where the energy gained from photosynthesis equals that lost in
the process of respiration so that no net growth can occur. Between the light compensation point and light saturation point
any increase in light will increase the rate of growth; however,
the ideal situation is to remain closer to light saturation than
light compensation.
Having too much light for photosynthesis can occur in indoor
gardens as well—more commonly with younger plants or with
those that have been grown under lower light and then planted
out under a greater light intensity.Very high light intensities will
break down chlorophyll, imparting a white, bleached appearance to the leaves and resulting in a decreased ability to carry
out photosynthesis.
Limiting factors
In an indoor garden the most likely limiting factors for photosynthesis—apart from a lack of light intensity or light of unsuitable wavelengths—are the availability of carbon dioxide and
temperature control. If temperatures become too high, plants
will effectively shut down photosynthesis as the stomata (pores
in the leaf that allow gas exchange) close to conserve moisture
and prevent desiccation. Closed stomata prevent CO2 from the
air diffusing into the leaf and so photosynthesis will stop. Low
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Very high light intensities will break
down chlorophyll, imparting a white,
bleached appearance to the leaves and
resulting in a decreased ability to carry
out photosynthesis.
temperatures have a similar effect—since the rate of enzyme reactions within a plant is temperature dependent, photosynthesis
will slow when conditions are cooler than optimal and will be
most rapid when temperatures are ideal for the particular plant
species being grown.
Carbon dioxide is also a limiting factor—particularly in enclosed indoor growing spaces—and CO2 depletion in densely
planted indoor gardens or even in closed greenhouses is common. Plants can rapidly strip CO2 from the air surrounding
their leaves under good light conditions when high rates of
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Maximum Yield USA | March 2012