A Mishna in masechet Shabbat2 lists kotzer (reaping) as one of the avot melachot. The definition of kotzer is detaching a living thing from its source of nourishment3. This melacha applies even to things that are not growing from the ground. For example, the Gemorah says that a person transgresses Shabbat if he removes mushrooms that grow on the edge of a bucket, since they receive their nourishment from the water that is located there4.