I dont think , theres is any relation beteen these parameters , unless the palnts are exposed to severe stress...

following

How should they be related under severe shading stress? Kindly guide.

Dear Darshan,

under deep shade you may expect plants to undergo a reorganization of their photosynthetic apparatus at many levels, from the morphological one to the biomolecular one. The extent of this response may depend also on the time during which the plant has undergone low light. However, regarding your question, a general response of plants to shade is a lower Chl a/ b ratio, which is indicative of a higher investment in antenna complexes (or, at least, a lower disinvestment in antenna complexes, if the resources are scarce), where chl B is located. A shade-acclimated plant should also display high values of Fv/Fm, because its potential photochemical efficiency is not affected by those processes that may be generally considered the cause of chronic photoinhibition, which may be induced under prolonged exposure to high photon flux density. Last: obviously, in shaded environments ETR is limited by the low light energy.