Abstract
15N tracing technique was applied to investigate the effects of various organic carbon (OC) sources on dissimilatory nitrate (NO3-)reduction to ammonium (NH4+) (DNRA) rates in the coastal wetland sediments. Soils collected from the Chongming Dongtan wetland were incubated at 25oC in the dark for 24 h following the additions of OC sources (glucose, acetate, malate, citrate and oxalate (500 μg C g-1 dry soil)) and 15N-labeled NH415NO3 (initial 15N atom% of NO3--N is 20%). The results showed that soil DNRA rates varied from 0.018-0.497 mg N kg-1 dry soil d-1during the whole incubation, and the rates differed significantly among treatments following the order: oxalate> citrate> glucose> acetate> malate> no exogenous C addition over the first 12-h incubation. This was possibly caused by the different decomposition rates of various OC sources, which further influenced the available energy provided for DNRA microorganisms. Soils with no addition of exogenous C showed lower soil DNRA rates, presumably because of the low C/NO3- ratio as well as energy availability. The relative lower soil DNRA rates over the 24-h incubation indicated that DNRA is a fast process. Our results suggest that DNRA could be controlled by OC sources, especially organic acids, demonstrating that the widespread use of glucose in soil laboratory studies might lead to misleading knowledge on understanding the effects of OC on soil DNRA process.
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