Effects of synthetic nitrogen fertilizer and manure on fungal and bacterial contributions to N2O production along a soil acidity gradient.

ABSTRACT

Reactive nitrogen (Nr) input often induces soil acidification, which may in turn affect bacterial and fungal nitrogen (N) transformations in soil and nitrous oxide (N2O) emissions. However, the interactive effects of soil acidity and Nr on the contributions of bacteria and fungi to N2O emissions remain unclear. We conducted a field experiment to assess the effects of anthropogenic Nr forms (i.e., synthetic N fertilizer and manure) on bacterial and fungal N2O emissions along a soil acidity gradient (soil pH = 6.8, 6.1, 5.2, and 4.2). The abundances and structure of bacterial and fungal communities were analyzed by real-time polymerase chain reaction and high-throughput sequencing techniques, respectively. Soil acidification reduced bacterial but increased fungal contributions to N2O production, corresponding respectively to changes in bacterial and fungal abundance. It also altered bacterial and fungal community structures and soil chemical properties, such as dissolved organic carbon and ammonia concentrations. Structural equation modeling (SEM) analyses showed that the soil properties and fungal community were the most important factors determining bacterial and fungal contributions to N2O emissions, respectively. The fertilizer form markedly affected N2O emissions from bacteria but not from fungi. Compared with synthetic N fertilizer, manure significantly lowered the bacterial contribution to N2O emissions in the soils with pH of 5.2 and 4.2. The manure application significantly increased soil pH but reduced nitrate concentration. The fertilizer form did not significantly alter the bacterial and fungal community structures. The SEM revealed that the fertilizer form affected the bacterial contribution to N2O production by changing the soil chemical properties. Together, these results indicated that soil acidification enhanced fungal dominance for N2O emission, and manure application has limited effects on fungal N2O emission, highlighting the challenges for mitigation of soil N2O emissions under future acid deposition and N enrichment scenarios.