English: In the figure above, sunlight and carbon dioxide from the atmosphere are absorbed by the leaves in the plant and converted to fixed carbon. This carbon travels down into the roots of the plant, where some travels back up to the leaves. The fixed carbon traveling to the root is radiated outward into the surrounding soil where microbes use it as food for growth. In return, microbes attach to the plant root where it improves the roots access to nutrients and its resistance to environmental stress and pathogens. In specific plant/root symbiotic relationships, the plant root secretes flavonoids into the soil which is sensed by microbes, where these microbes release nod factors to the plant root which promotes the infection of the plant root by microbes. These unique microbes carry out nitrogen fixation in root nodules, which supplies nutrients to the plant.