From the highest shoot tip to the farthest reach of the root tips, every part of the tree must have oxygen. Using oxygen from the atmosphere can be difficult for stems, leaves, and roots. Most woody parts of a tree have water-proof bark. Bark has gas exchange openings called lenticels. Tree leaves are thin and held in the air, but are covered with a protective, interlocked surface with a wax coating.
Tree roots are in a terrible spot for capturing oxygen.
Root Plight Roots are in a moist, dark soil environment that has many sizes of pores between both structural units and between particles. Small-sized pores between the solid mineral materials are filled with water. Large-sized soil pores are filled with air. These large, interconnected air-filled pores allow oxygen to move into the soil and to the roots. Oxygen can then be used for root respiration.