Answer:
Deforestation reduces the amount of oxygen present in air and thereby, disturbs the oxygen cycle by reducing the oxygen content in its reservoir (the air).
Step-by-step explanation:
Air serves as reservoir for oxygen in the oxygen cycle.
Plants serve to release oxygen in the air. The oxygen is taken by both animals and plants for breathing. Hence, presence of plants in the system replenish the oxygen in the air which is otherwise taken by living organisms for breathing.
Deforestation cuts down large number of trees. Less number of plants add lesser oxygen to the air and hence, the oxygen content of the air is reduced.