Air and Water Cycles

How do you compare oxygen production of various plants? I've been looking into
this and so far have not found a sufficiently satisfactory answer.

I have to assume however that not all plants are equal when it comes to
photosynthesis, which is primarily done by chloroplasts in leafy parts of
plants. According to Wikipedia, a square millimeter of leaf can contain between
450,000 and 800,000 chloroplasts.

The first problem is how to even compare one plant to another. Obviously a big
plant should produce more than a small plant of the same type. So probably
plants should be compared by mass. However, photosynthesis is also mediated by
insolation/lighting so leaf area may presumably need to be normalized as well.
Thoughts, anyone?

The second problem is how to measure oxygen levels. There are some COTS oxygen
sensors out there that typically run in the hundreds of $$. My goal is to avoid
them. One option that occurred to me is to recycle the O2 sensors from vehicular
exhaust systems. However, I believe they generally work at higher temperatures.
I've also considered simpler methods along the lines of this steel wool experiment.

Any true CELSS will need to monitor oxygen levels. Does anyone here have
experience with how to do this? Canaries? :)

As far as measuring plant productivity, it has occurred to me that there may be
some indirect methods. Since the photosynthesis reaction
produces biomass, it may be
possible to measure productivity by weighing the plant along with its soil and
pot, so long as water is carefully accounted for. A hydroponic setup would not
work, since additional nutrients (nitrates) would be getting absorbed by the
plant without any way to measure them separately.