Maximum Yield Cannabis Canada 2017 July/August | Page 49

“MEASURING LST IS like taking
a person’s temperature with a
thermometer under their tongue.”
Note that the leaf surface temperature
is affected by, but not equivalent to, the
ambient air temperature in the growing
environment. Leaves can be cooled through
evaporation occurring in open pores
(stomata) in the leaf that allow gas exchange,
and are warmed by absorbed but unused
light, whether from artificial or natural sources.
Leaf surface temperature is almost always
different than ambient air temperature.
WHAT IS THE IDEAL LEAF SURFACE TEMPERATURE?
So, what is the ideal leaf surface temperature for plants? This
is unfortunately a question without a simple answer as many
factors influence the ideal.
Multiple types of metabolic reactions exist within every
plant, and each has a different optimal temperature range.
Primary metabolism (photosynthesis) is obviously the most
important; without it, the plant will not survive. Optimal
temperatures for desirable secondary metabolites must
be considered as well, especially if the plant is grown
specifically for the secondary metabolites.
The optimal leaf temperature range for photosynthesis
depends on the type of plant and concentrations of CO 2 .
Arctic- and alpine-adapted plants typically require cooler
temperatures, while desert-adapted and plants using C4
photosynthesis prefer it warmer. (There are two slightly
different chemical reactions for photosynthesis, called C3 and
C4; the variant a plant uses is determined genetically.) Most
growers also know they can turn up the temperature when
running CO 2 , since CO 2 supplementation will generally raise
the optimal photosynthesis temperature. Thus, the ideal LST
for photosynthesis is dependent on environmental conditions
as well as the type of plant.
Secondary metabolic reactions can have a huge range
of optimal temperatures; many plants have even evolved
responses specifically triggered by exposure to cold or hot
temperatures to better adapt to their surroundings. For
example, some plants produce proteins with anti-freeze
properties when exposed to cold.
In short, the ideal leaf surface temperature depends on
the species/variety of the plant, overall environmental
conditions, as well as what the plant is being grown for. Only
experimentation can determine an ideal range for LST for a
specific plant variety in a specific set of conditions.
grow cycle
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