Open AccessEffects of nitrate, nitrite, NO and N 2 O on methanogenesis and other redox processes in anoxic rice field soil
Author(s) -
Klüber H.Detlef,
Conrad Ralf
Publication year - 1998
Publication title -
fems microbiology ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.377
H-Index - 155
eISSN - 1574-6941
pISSN - 0168-6496
DOI - 10.1111/j.1574-6941.1998.tb00482.x
Subject(s) - methanogenesis , nitrate , nitrite , denitrifying bacteria , anoxic waters , electron acceptor , denitrification , environmental chemistry , methanogen , exergonic reaction , electron donor , chemistry , biology , inorganic chemistry , biochemistry , methane , ecology , nitrogen , organic chemistry , catalysis
We studied the inhibitory mechanism of nitrate and its denitrification products (nitrite, NO, N 2 O) on the production of CH 4 and the concentrations of reductants (H 2 , acetate, propionate, etc.) and oxidants (NO − 3 , NO − 2 , NO, N 2 O, Fe(III), SO 2− 4 ) in slurries of anoxic Italian rice soil. Addition of each of the N‐compounds caused a complete but largely reversible inhibition of methanogenesis. Nitrate, nitrite and N 2 O significantly decreased the H 2 partial pressure. With nitrate and N 2 O it decreased below the threshold of methanogens, thus not allowing exergonic production of methane (ΔG>0). Furthermore, significant production of the electron acceptors Fe(III) and/or sulfate was observed after addition of nitrate and N 2 O, probably due to the oxidation of reduced iron and sulfur species with nitrate and/or N 2 O as electron acceptors. Methanogenic activity did not resume until all electron acceptors were reduced and, as a consequence, H 2 had reached the methanogenic threshold again. Thus competition for H 2 with denitrifying bacteria, iron‐ and sulfate‐reducing bacteria seemed to be one important factor for the inhibition of methanogenesis. Addition of rice straw to reduce competition for electron donors did not prevent inhibition of methanogenesis after addition of nitrate but decreased the inhibition period. Especially after addition of nitrite and NO, toxic effects may have been more important than competition. Although addition of nitrite or NO caused a decrease of the H 2 concentration, exergonic methanogenesis from H 2 /CO 2 was always possible (ΔG<0). Nevertheless, CH 4 production was inhibited. Furthermore, acetate concentrations were generally sufficient for exergonic methanogenesis in all experiments, even so CH 4 production was completely inhibited. Turnover times of [2‐ 14 C]acetate to 14 CH 4 were higher in soil slurry that had resumed methanogenesis after nitrate inhibition than in the untreated control indicating toxic effects on acetate‐utilizing methanogens. However, since the contribution of 14 CO 2 reduction to CH 4 was almost the same (26–29%) in soil slurry that had resumed methanogenesis after nitrate inhibition as in the untreated control, hydrogenotrophic methanogens must have been affected by toxic N‐compounds to a similar extent as acetoclastic methanogens.