Phosphate Inhibits Acetotrophic Methanogenesis on Rice Roots

The contribution of acetate- and H(2)/CO(2)-dependent methanogenesis to total CH(4) production was determined in excised washed rice roots by radiolabeling, methyl fluoride inhibition, and stable carbon isotope fractionation. Addition of > or = 20 mM phosphate inhibited methanogenesis, which then was exclusively from H(2)/CO(2). Otherwise, acetate contributed about 50 to 60% of the total methanogenesis, demonstrating that phosphate specifically inhibited acetotrophic methanogens on rice roots.