How do plants get rid of decay products that are formed in the process of dissimilation and harmful substances?

We can observe the process of getting rid of plant decay products every fall. This is a common leaf fall. You can do an experiment. If you pluck a leaf, it will simply dry out, but not change color. In autumn, the castings do not dry out, but first change color before falling off. This is due to the fact that the tree throws all harmful and unnecessary substances into the leaves. Therefore, they turn yellow or red. After some time, they separate from the tree and can be recycled by worms and bacteria for reuse by the tree.