During autumn, the leaves of the plants turn red and fall, resulting in complete defoliation of the trees. which mechanism is taking place? . . dormancy. . senescence. . photoperiodism.

Dormancy

The phenomenon wherein the leaves of the plants turn red and fall during the autumn season followed by the defoliation of trees is a concrete example of dormancy. Dormancy refers to the time wherein plants don't grow and wait for necessary environmental factors like moisture, temperature and others. 

Answer the above statement is correct (true);