at lights out with a/c off on the other hand it spikes and dehuey comes on.This is sealed room of course.
I have seen this with CO2 enhancement levels ( 1200-1500ppm ) in my sealed room data, a distinct 'vapor dump' spike that needs cleanup at lights off. CO2 Transpiration ceases ( if you monitor the CO2 level, you can see it stop promptly ) however there seems to be a reserve left in the vascular system that continues. There also is the CO2 molecule to water molecule ratio, so perhaps a reduction in CO2 before lights off would head off the vapor dump. Our artificial light sources are rather digital ( on or off ) and that is probably a factor. No ramp-down (sunset) to wind down activity - so some anomalous curve should be expected on plant response in transpiration when the light snaps off.
Carbon dioxide entry: When a plant is transpiring, its stomata are open, allowing gas exchange between the atmosphere and the leaf. Open stomata allow water vapor to leave the leaf but also allow carbon dioxide (CO2) to enter. Carbon dioxide is needed for photosynthesis to operate. Unfortunately, much more water leaves the leaf than CO2 enters for three reasons:
- H2O molecules are smaller than CO2 molecules and so they move to their destination faster.
- CO2 is only about 0.036% of the atmosphere (and rising!) so the gradient for its entry into the plant is much smaller than the gradient for H2O moving from a hydrated leaf into a dry atmosphere.
- CO2 has a much longer distance to travel to reach its destination in the chloroplast from the atmosphere compared to H2O which only has to move from the leaf cell surface to the atmosphere.
This disproportionate exchange of CO2 and H2O leads to a paradox. The larger the stomatal opening, the easier it is for carbon dioxide to enter the leaf to drive photosynthesis; however, this large opening will also allow the leaf to lose large quantities of water and face the risk of dehydration or water-deficit stress. Plants that are able to keep their stomata slightly open, will lose fewer water molecules for every CO2 molecule that enters and thus will have greater water use efficiency (water lost/CO2 gained). Plants with greater water use efficiencies are better able to withstand periods when water in the soil is low.
Water uptake: Although only less than 5% of the water taken up by roots remains in the plant, that water is vital for plant structure and function. The water is important for driving biochemical processes, but also it creates turgor so that the plant can stand without bones.