When other conditions are correct, the rate of
photosynthesis (sugar
production) doubles for each 10oC rise in temperature. This
principle applies within the 10-30oC range for temperate plants
and 15-35oC for tropical plants.
Optimum air temperature for plants
When growing in an enclosed area (i.e. grow
room or greenhouse), air temperature
is typically controlled via artificial heating,
ventilation or fogging.
+
Day time: The optimum daylight temperature is around 25oC.
Never allow the temperature to exceed 30 - 35oC because this
can cause photo respiration which results in the wasteful destruction of
sugar supplies thereby slowing growth rates. Conversely, lower
temperatures (i.e. below 25oC) will suppress the rate of
photosynthesis and respiration which will restrict essential plant
processes and growth. Low temperatures can also cause humidity to
increase to levels which could promote disease problems. Further,
cold leaves will suppress transpiration rates which restricts nutrient
uptake. Translocation is also a lot slower when the temperature is much
below optimum causing systemic agents (e.g. foliar fungicides) to act more
slowly.
+
Night time: The optimum daylight temperature must be allowed to drop
by at least 5oC at night i.e. to 20oC. Because
plants do not photosynthesise at night they require less ATP energy (“ATP
energy” is used for downloading sugars, nutrient uptake etc.) and
therefore such high respiration rates are not necessary. Since plants
cannot store ATP, any excess that is produced is wasted. Therefore to
suppress the respiration rate at night, the atmospheric temperature must
be allowed to drop.
