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Maybe @Homesteader or @glo or another one of the science types could chime in.There absolutely should be... the problem is that we still don't know the maximum ppm of co2 or ppfd at which benefits are the highest in order to really do this. I have a lot of trouble finding studies that go beyond 1500ppfd or over 800ppm co2. Personally I max my co2 out about 1200ppm and haven't seen any benefit beyond that. Bit thats not to say there isn't. Just I cant see it visually it if there is.
I would say with its between 5-10% lower RH depending on light and co2. Its also a balancing act if nutrient uptake and temp. So many moving parts, even the genetics. I grow hybrids and depending on whether they lean more indica or sativa also makes a difference. This is why VPD is a guide and not a hard rule and I would say understanding the concept and the moving parts involved is much more beneficial than just going by the numbers. I can say my experience is the more light you provide the more crucial the VPD becomes.
Its really good as a tool but not an absolute.
I've run 1250ppm for many years, the only time I had any concern about RH is if it was too high. About a year, year and a half ago after not being able to turn around without hearing about VPD being the holy grail of environmental factors, I spent thousands on commercial hard plumbed humidifiers, their controllers and remote hygrometers hanging all over the place reporting back to headquarters. My honest results of it all are butt loads of dehumidifiers working overtime during lights out and the inability to grow any strain remotely sensitive to PM.
I'm not saying VPD is hogwash but I sure would like to understand in dumb guy terms how it relates to CO2.