Nodules (IMAGE) Chapman University Caption A cluster of nodules on the roots of the plant Lotus japonicus. Bacterial rhizobia are housed within root nodules and supplied with carbohydrates from the host plant. The carbohydrates are used by rhizobia in exchange for the fixation of nitrogen then used by the plant. Credit K. Quides Usage Restrictions image may be used with credit License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.