A plant’s leaf surface temperature (LST) is determined by a variety of factors such as plant type, light spectrum, humidity, and air temperature.
In order for a plant to produce and yield an ample crop, its leaf temperature must be kept at ideal.
The act of raising ambient air temperature approximately 9 °F to 10 °F can result in an equivalent leaf surface temperature compared to growing the plant under high-power HPS and MH lights. (that radiate/project heat unlike LED's).When considering air temperature versus LST, think of things this way.
Measuring the ambient air temperature in the grow room is like measuring the air in our living environment; it is important for us to have a proper temperature to live in.
By comparison, measuring LST is like taking a person’s temperature with a thermometer under their tongue.
It tells us what’s going on inside the person and gives us a good indication of that person’s health.
By carefully monitoring LST inline with ambient air temperatures, this gives growers a better indication of what is occurring in their crop.
Why does leaf surface temperature matter and why should gardeners look into measuring this?
Leaf Surface Temperature (LST) helps determine the actual temperature of the plant, which is different to the ambient temperature of your growing environment, although the environmental temperature will also play a role in the temperature of your plant.In most plants, leaves play a key role in a plants metabolism, if a plant's leaves are at an optimal temperature, the plant will reach its maximum potential for growth through temperature alone, but obviously there is many other factors that will determine a plants true potential for growth overall.
Most educated and experienced growers are always looking for ways to optimize their gardens for that perfect grow, as environmental conditions and temperatures play a big role in the success or failure of plants growth.
How to measure your Leaf Surface Temperatures
Measuring your LST can be effectively achieved with tools such as FLIR Cameras or Infrared Thermal Imaging cameras or meters. The most accurate way to measure LST would be using a FLIR Thermal Camera, as the surface temperatures can vary across surfaces of each leaf, this would allow you to see the true temperature variance of each leaf. A FLIR Thermal Camera can be had for a couple hundred dollars, they used to cost many thousands of dollars.
A cheaper alternative to measure your LST is by using a Infrared Thermometer, although this will only measure temperatures at a single point. When taking measurements of temperature using an Infrared Thermometer, it may be worth reading several points per leaf to get a better idea of the surface temperature.
An Infrared Thermometer can usually be found for $15 on up for the hobbyist grower and can be a very useful tool for checking other temperature points of your environment and reservoirs.
What is the optimal Leaf Surface Temperature?
Unfortunately this is not an easy question to answer, as there is too many additional variables that play a part in this. Many factors, such as: plant type, concentrations of CO2, strains variations, etc. all factor in determining the exact optimal LST.
For many plants, the leaf temperature range for photosynthesis would be between 15c celsius and 30c celsius (59F - 86F) on average with normal atmospheric concentrations of CO2, this range would increase as the levels of CO2 increased within the environment.
Studies have shown that when growing using LED horticultural lights, leaf surface temperature (LST) is lower than using traditional HID lighting, usually resulting in the LST being lower than optimal under LED lights.
By not wasting energy producing light of no use to the plant, LED grow lights are vastly more efficient than HPS and other traditional artificial plant lighting technologies.
This has important implications on required environmental conditions to maintain optimal plant growth-- plants grown under LED plant lights require a warmer environment.
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 CO2. 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 CO2, since CO2 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.
A work in progress,
Vandenberg
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