VPD Chart for CO2

Photosynthesis by day, Cellular respiration by night. Co2 doesn't change the parameters of the environment that are suitable for the plant. Co2 increases the efficiency with which the plant can convert stored energy into carbo(sugar)hydrates(water). Max energy a plant can convert in any one cycle is 40 mole per day at 400 ppm. 60 mole per day at 12-1800 ppm. Notice that light intensity, carbon dioxide concentration, and temperature are the three main factors that impact photosynthesis. Greater light intensity leads to higher photosynthesis rates, as does increased carbon dioxide concentration. Temperature is also directly linked to the rate of respiration Q10 Temperature coefficient. This is a key factor affecting photosynthesis. Low CO2 affects the Calvin Cycle. If CO2 levels are low, rubisco cannot convert RuBP to GP in step one of the Calvin Cycle. This leads to the accumulation of RuBP and an overall slowing of the Calvin Cycle, which results in a fall in the production of TP/GALP. CO2 is not needed at night so turn it off. Nights should be focused on respiration and dealing with excess moisture spat into the air all night long, keeping ambient canopy RH 40-45%. This keeps a constant negative pressure overnight. Oxygen is what a plant needs at night, only oxygen diffuses into the leaves and only carbon dioxide diffuses out. Vpd is just a measure of temperature and humidity. The drier the air the more space it has to spit more moisture out. As soon as those lights go out she is just spitting moisture. All the energy the plant collects during the day must be processed overnight. Grow tents at night reaching upward of 65%RH or thereabouts things start to drift from optimal. If the plant only converts a percent of all the energy it gathered during the day and doesn't process it all that night, the plant keeps a surplus which will detract from the next day's DLI. I was surprised, stunned even at how much more water she needed to maintain the intense daytime cooling. Daytime priority is keeping temps under 86 and hitting a DLI of 40-60moles, supplement CO2. Nighttime is about maxing out the rate of respiration and getting rid of water ASAP. To make use of all the energy stored in the stems the plant needs to convert a lot of the stored energy to sugars then the plant mixes them with nutrients to make more complex cells, more nutrients, and more water until there is no energy left stored in those stems. If we don't optimize night cycle, like everything else with cannabis plants, the entire production of the plant as a whole will bottleneck at the place in the line that is least efficient. At night If you can stick to 40-45%RH, you should keep semi-optimal turgor pressure, negative pressure, and humidity for quick removal of water vapor generated under the stomata. Keeping 40-45 % should mean keeping temps around 73-83 and keeping your VPD in the "green" for most of the flowering period. I kinda think of it like PH, 6.5 is not the best for every nutrient but it's about balance across the spectrum of variables. VPD is similar. Becomes very hard to micro-manage if you focus on too many controllers its hard to keep everything perfect always. You can't keep it perfect 100%, all the time, well you can but the electrical cost of doing so very quickly changes your mind as electrical components sensors start fighting each other cycling 24/7. If your plant is only dealing with 40% of the energy it stores from the daylight hours because respiration levels are low then you are running at 40% of total "work done" for everything no matter what you do or how you feed or anything. 9 cardinal rules of growth all must run in unison, if any 1 runs at 10% efficiency then everything else will bottleneck to that 10%. That's not even taking into consideration the feeding plan....if you're feeding concentrate you need to calculate for that, the mind boggles. I made the decision to pack everything the plant will ever need and then some into the soil, letting the plant dictate its own feeding schedule based on the demand the environment places on it.