POWERING PHOTOSYNTHESIS
With the stomata shut to prevent water loss,
photosynthesis cannot occur, as CO2 can’t
be taken in from the surrounding air. Plant
growth and yield will be slowed if this
occurs too often.
When humidity is low, particularly when
combined with warm growing conditions,
it can be difficult to tell if plants have shut
down photosynthesis due to closed stomata,
as under these conditions, the foliage may look normal. One
way of checking to see if the stomata are open is to measure
the difference between leaf surface and air temperature
using a handheld infrared thermometer. A plant with
open stomata is actively cooling itself via transpiration, so
the leaf surface will be a slightly lower temperature than
the surrounding air. If the leaf surface is warmer than the
surrounding air, then transpiration is not occurring and
photosynthesis has shut down.
An infrared thermometer can be used to determine leaf temperature
and whether the stomata are open for CO2 uptake.
Along with light quality and
quantity and CO2 levels,
temperature also determines
the rate of glucose production
during photosynthesis.”
Tomato plants respond well to CO2 supplementation.
Light and Temperature
Low-light symptoms include plant elongation and stretching.
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Maximum Yield USA | December 2015
Along with light quality and quantity and CO2 levels,
temperature also determines the rate of glucose
production during photosynthesis due to the activity of
enzymes that catalyze biochemical reactions in leaf tissues.
These enzymes are strongly affected by temperature, so
the rate of assimilate production through the process
of photosynthesis is maximized when the plant is grown
in its optimal temperature range. At low temperatures,
which for many plants we commonly grow is 32-50°F, the
enzymes involved in photosynthesis do not work at full
efficiency and this lowers the rate of sugar production
and plant yields. At optimal temperatures, which vary
for different species, but are often between 50 and 75°F,
photosynthetic enzymes work at their maximum rate.
At these temperatures, it is often the diffusion of CO2
that becomes the limiting factor for photosynthesis. At
high temperatures (104-113°F), many plant species will
experience a drop in photosynthetic rate.