Answer
We would need to know how long the plants were kept at each of the temperatures.
Work Step by Step
In order to determine if the AFP is useful in protecting against frost damage, we would need to know how long the plants were kept at each temperature, as if they were only kept at each temperature for a short period of time (i.e. a few minutes) then this wouldn't indicate how much damage the plants would sustain if actually grown in those temperatures.
