One method of determining the natural photoperiod is to obtain sunrise and sunset data for your species in its native location, then assume that plants perceive light inside the greenhouse about 15-20 minutes before sunrise that ends about 15-20 minutes after sunset. Then you can create short days and long days, depending on the effect desired and whether your plant flowers in long or short days.

Yes, photoperiod does affect nutrient concentrations. In one study, the largest photoperiod reflected in a higher average rate of reduction of nutrients, in two plant species. See: Rev. Bras. Biol. vol.60 no.3 São Carlos Aug. 2000, http://dx.doi.org/10.1590/S0034-71082000000300002

Dear Svetoslav,

thanks a lot! I'm working on artichoke tissues and I am trying to understand why different photoperiodic treatments are influencing C H N distribution.

I will read carefully the chapter you are suggesting.

Thanks a lot!!!

Sara