3 important factors

a. shading

b. general variations in PAR values interlaced with temperature changes

c. nitrogen status

Nutritional and available exposure(sunshine) hours

While comparing the response of nutrients versus phytoharmones , there will always be much higher magnitude of response with the combination of the two than either of the two , alone. So will be the case with chlorophyll a/b ratio. Needless to say , nutrients like N, Fe, Mg , have much decisive role to play in guiding the changes in chlorophyll a/b ratio....

water temperature

3 important factors

a. shading

b. general variations in PAR values interlaced with temperature changes

c. nitrogen status