Dear Ibrahim, the chl a/b ratio could be an indicator of excess energy. Please see: Ogbaga, C.C., Stepien, P., Johnson, G.N., 2014. Sorghum (Sorghum bicolor) varieties adopt strongly contrasting strategies in response to drought. Physiol. Plant. doi:10.1111/ppl.12196
The ratio betwen chl a and b it depend of grade of radiation that the plant receive, plants in the shadows could have a ratio below 1 and in the sun this ratio increase.
Cholophyll b traps the light energy and pass on to chlorophyll a. Chlorophyll b’s main function is to collect energy from the blue spectra but an important secondary function is to regulate the light harvesting antenna size. Chlorophyll beta is found only in peripheral light-harvesting complexes (LHCs) and in nearly equal amounts between Chl a and Chl b. Then chlorophyll a also occupies the reaction center of the antenna array and is required for assembly of these complexes around it...
In some literature, I have found that age of the leaves have also a significant impact on ratio of Chl a and b. I also would like to know, is it true??