This assumes that during a water change, plants are exposed to air.

What about plants below the water line? They are not exposed to gas phase CO2, but seem to pearl more after a water change regardless.

Why not repeat experiment #1, draining the tank to just above the hairgrass, thereby not exposing the plants to air.

If the theory holds, there should be no increase in pearling.

This topic really interests me because of odd observations made on my tank recently. As i posted previously, to combat murky water, I've been injecting air into my system at night. A couple of days ago, I upped the air from 1 bubble every 3 seconds to 2-3 bubbles per second.

At 8:00 am the next day, before the lights came on, and before the CO2 came on, the plants were already pearling like mad. It was not just sticky air bubbles coming through from the air pump. I could see streams of bubbles coming from the plants. This was without light, so there should have been no photosynthesis. There must have been CO2 gas in the water just from the air pump, but how can plants produce O2 without light? I can reproduce this effect very easily just by adjusting the amount of air injected into the system at night.

Makes me think that there may be more to pearling than just photosynthesis.