SULFATE REDUCTION AND A MOLYBDATE-INDUCED SOLUBLE NITROGEN FLUSH IN SEDIMENTS DURING INCUBATION

It has been known that molybdate inhibits sulfate-reducing bacteria (S RB). We observed a significant increase in soluble N from a salt marsh sediment sample after. molybdate-treated (MT) incubation when it was compared with the control. This observation led to an investigation in to the source of this N flush from the sediment. The amount of the ext ractable N released during a MT incubation at 35 degrees C increased w ith time up to 7d reaching a plateau. The extractable N was mainly in organic forms during the first week of incubation followed by a quick conversion to ammonium N within 3d. The pattern and forms of the incre ased extractable N during the MT incubation suggest an organic N sourc e in the system induced by MT incubation. The net increase in extracta ble N during the MT incubation, i.e. the increased extractable N after correction for the control, is positively correlated with the sulfate reduction rate of the sample. We propose that the net increase in ext ractable N induced by the MT is a quantitative indicator of the SRB bi omass N and its ratio to the net chloroform-fumigation-extraction N is an indicator of the SRB biomass N-to-total microbial biomass N ratio in a sediment. (C) 1998 Elsevier Science Ltd. All rights reserved.