The plant-microbial fuel cell (P-MFC) is a new technology for sustainable and in-situ production of electricity from living plants (Strik, 2008). The P-MFC makes use of electrochemically-active bacteria that catalyse the anaerobic oxidation of rhizodeposits at the roots of plants. By connecting the plant roots and bacteria directly to an electrical circuit, current will flow as a result of oxygen reduction at the other end of the circuit.
http://waternexus.nl/research/p-mfc/