POWERING PHOTOSYNTHESIS
Photosynthesis
When light falls on a plant leaf, it
provides the energy for the production
of sugars or assimilates from water and
carbon dioxide, which is absorbed from the air
through the stomata on the leaf surface. Oxygen is
released as a by-product, making photosynthesis the source
of much of the oxygen in our atmosphere. This process is
summarized by the fully balanced equation:
6CO2 + 6H2O + light energy ------> C6H12O6 + 6O2
The glucose (sugar) produced during photosynthesis is
transported around the plant and used for growth and
development, or it may also be stored for later use. The most
well-known light-absorbing pigments are chlorophyll a and
chlorophyll b. But chlorophyll a and b are not the only lightharvesting pigments in plants, there are also a number of
accessory pigments that allow photosynthesis to use a large
proportion of the visible light spectrum.
Photosynthesis and CO2
Along with light, carbon dioxide (CO2) is also required
for photosynthesis, but CO2 only makes up a fraction of
our atmosphere—around 365 ppm, or 0.036% by volume.
Despite this, dried plant materials contain on average 45%
carbon, which comes from CO2 through the process of
photosynthesis. Therefore, carbon dioxide is a major plant
nutrient, one that affects both photosynthesis and crop
yields, and it needs to be supplied in adequate quantities
to maximize plant growth. Providing indoor gardens
with supplemental CO2 can result in yield increases
of more than 40% under some conditions. However,
supplementation must be done carefully, as a level of CO2
enrichment suitable for a mature tomato plant under
strong lights may damage small, weaker seedlings under
Along with light quantity and quality, CO2 and temperature also
determine the rate of photosynthesis.
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Maximum Yield USA | December 2015
Chlorophyll is the main light-harvesting pigment in plants.
Carbon dioxide is a major
plant nutrient, one that
affects both photosynthesis
and crop yields.”
less intense illumination. Too little CO2 will cause plants
to stagnate and photosynthesis to grind to a halt; too
much can cause toxicities, stunting, leaf curling and
other damage, which is often hard to define or diagnose.
Carbon dioxide levels also interact with other factors
to impact the photosynthesis rate. As temperature
and light levels increase in the growing environment,
the rate of photosynthesis and absorption of CO2 also
increases, up to a maximum level. The rate will also
increase with CO2 concentration, up to a point where
some other factor, such as the peak speed at which plant
enzymes will work, is also reached.
Indoor growers need to ensure carbon dioxide in the
growing environment does not become depleted, as this
would slow the photosynthesis process. Carbon dioxide
deficiency is a common occurrence in many hobby
greenhouses and indoor gardens because every effort has
been made to prevent heat loss by sealing the growing
area up tightly. Adequately venting the growing area will
prevent CO2 depletion, but the rate of air replacement
required in a densely planted, mature crop in a small,
confined growing area can be much higher than most
growers realize when the plants are growing under strong
lights and actively photosynthesizing.