The function of the roots includes water absorption and uptake of oxygen from the pore space (the space between soil particles) of the soil. When soil is water logged, all the pore spaces are filled with water and oxygen is pushed out of the soil. Oxygen from the pore spaces move into the atmosphere. So, in water logged soil, the plants do not grow well as the roots of the plants do not absorb oxygen. This stops the respiration and production of energy. As a result the plant dies after some time in absence of oxygen.