Effect of acetate on soil respiration, N2O emissions and gross N transformations related to fungi and bacteria in a grassland soil

Application of organic carbon to grassland in the form of manure or cattle slurry during the growing season is a normal agricultural practice. Under enhanced organic C supply changes in the grassland soil's internal N cycling and in the microbial community are expected, in particular, the fungi–bacteria ratio. Here we present novel results from a 15N tracing study which aimed to investigate the role of fungi and bacteria in N transformations under enhanced organic C supply. We applied 15N labelled fertiliser to soil in a laboratory incubation with and without acetate addition. Moreover, we used specific microbial inhibitors to selectively inhibit either fungi or bacteria. The data from the incubation were used to calculate gross N transformation rates via 15N tracing models based on Monte Carlo sampling techniques. Our results show that fungi are the predominant organisms that carry out N transformations in a temperate grassland soil. Under enhanced organic C supply, the stimulation of the mineralization – immobilization – turnover and heterotrophic nitrification was predominantly related to fungal activity, indicating that fungi may play an increasingly important role in soils with an enhanced C supply. In addition, we showed that fungi were the dominant organisms for N2O production. Increased fungal activity under enhanced organic C supply may therefore increase N2O emissions from soil and have environmental consequences.