Phototrophic N2 fixation suppressed by activated sulfate reduction in anoxic rice soil slurries.
Interactions between sulfate reduction (SR) and phototrophic nitrogenase activities were investigated in rice soil slurries mixed with rice straw. Activation of SR by adding exogenous sulfate suppressed acetylene-reducing activity (ARA) of the slurries, which was associated with phototrophic purple bacteria (PB) enumerated to 108-109 MPN g-1 dry weight (dw) soil. Adding 5 mm sodium molybdate, an inhibitor of SR, markedly increased ARA. However, in the slurries receiving both molybdate and exogenous sulfate, the effects declined simultaneously with partial recovery of SR. These results indicate outcompetition of sulfate-reducing bacteria (SRB) with PB in rice soil, when sulfate concentrations are high enough to support SR. The increasing effects of molybdate on ARA continued during the incubation in the sulfate-depleted condition, probably because of absence of SR and toxicity of molybdate to methanogenesis. Accordingly, stopping activities of the competitive microorganisms may be efficient to increase N2 fixation in rice soil.
Harada
N
N
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. haradana@bc4.so-net.net.jp
Nishiyama
M
M
Matsumoto
S
S
D004791:Enzyme Inhibitors / Q000378:metabolism; D008982:Molybdenum / Q000378:metabolism; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000378:metabolism; D012275:Oryza / Q000382:microbiology; D010084:Oxidation-Reduction; D012987:Soil; D012988:Soil Microbiology; D013430:Sulfate Adenylyltransferase / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism*; D016999:Sulfur-Reducing Bacteria / Q000201:enzymology / Q000378:metabolism*
D004791:Enzyme Inhibitors; D012987:Soil; D013431:Sulfates; C044659:molybdate; D008982:Molybdenum; D009591:Nitrogenase; D013430:Sulfate Adenylyltransferase