Stimulation of heterotrophic nitrification and N2O production, inhibition of autotrophic nitrification in soil by adding readily degradable carbon

Abstract

This study aimed to test the hypothesis that readily degradable Carbon (C) has contrasting effect on soil N autotrophic and heterotrophic nitrification, can stimulate nitrous oxide (N2O) emission. The knowledge can improve our understanding of the effect of readily degradable C on soil N nitrification and the related N2O emission. 15N tracing technique along with acetylene inhibition was used to determine the effect of different doses of glucose-C addition on the rates of total nitrification (ntot), autotrophic nitrification (na), heterotrophic nitrification (nh), and N2O production in two soils. Soils were collected from Glenormiston (GN) and Terang (TR), Victoria, Australia and incubated at soil moisture content of 60% water-filled pore space (WFPS) and at 25 °C. The addition of mixed C and N substrates with wide C/N ratio (> 25) promoted heterotrophic nitrification by 2.84- to 3.33-folds but inhibited autotrophic nitrification by 30.4–54.8%, thereby resulting in high ntot and NO3− accumulation compared with the soil samples under the control treatment. The mechanism of glucose inhibition of na might be caused by increasing the microbial immobilization of NH4+ and not by affecting the gene copy numbers of ammonia-oxidizing archea and ammonia-oxidizing bacteria. The glucose addition stimulated N2O production in soil, which might be caused by promoting heterotrophic nitrification and denitrification. The stimulating effect of degradable C application on the contribution of heterotrophic nitrification to total nitrification, NO3− accumulation, and N2O production should be considered, especially in soils with low pH and high organic C content.