Please correct me if I'm wrong, and I probably am wrong.

Plants don't have a circulatory system. There is no circulatory loop
like with mammal blood. All moisture goes from the roots up. This is
caused by moisture evaporation from the leaves.

Theorhetically then, you could chop off a plant at ground level and
connect the stem to a vacuum suction pump and the roots wouldn't know
the difference, the roots would continue to grow.

What's wrong with this theory? Or might it actually work? If not then why?

Thanks for your help.