Plants need carbon dioxide to enable them to reproduce food by photosynthesis. They need oxygen so that they can respiration can take place in the cells. Respiration is the process of burning food to provide energy for growth. Obtain both these gases from the air around the roots. For the roots to obtain enough oxygen the soil must contain many pores filled with air. Root growth suffers in waterlogged soils because of the lack of oxygen. A few plants such as mangroves have special adaptions to enable them to live in swampy soil.