Abstract
Application of inorganic nitrogen (N) fertilizer and manure can increase nitrous oxide (N2O) emissions. We tested the hypothesis that increased N2O flux from soils amended with manure reflects a change in bacterial community structure and, specifically, an increase in the number of denitrifiers. To test this hypothesis, a field experiment was conducted in a drip-irrigated cotton field in an arid region of northwestern China. Treatments included plots that were not amended (Control), and plots amended with urea (Urea), animal manure (Manure) and a 50/50 mix of urea and manure (U+M). Manure was broadcast-incorporated into the soil before seeding while urea was split-applied with drip irrigation (fertigation) over the growing season. The addition treatments did not, as assessed by nextgen sequencing of PCR-amplicons generated from rRNA genes in soil, affect the alpha diversity of bacterial communities but did change the beta diversity. Compared to the Control, the addition of manure (U+M and Manure) significantly increased the abundance of genes associated with nitrate reduction (narG) and denitrfication (nirK and nosZ). Manure addition (U+M and Manure) did not affect the nitrifying enzyme activity (NEA) of soil but resulted in 39–59 times greater denitrifying enzyme activity (DEA). In contrast, urea application had no impact on the abundances of nitrifier and denitrifier genes, DEA and NEA; likely due to a limitation of C availability. DEA was highly correlated (r = 0.70–0.84, P < 0.01) with the abundance of genes narG, nirK and nosZ. An increase in the abundance of these functional genes was further correlated with soil NO3−, dissolved organic carbon, total C, and total N concentrations, and soil C:N ratio. These results demonstrated a positive relationship between the abundances of denitrifying functional genes (narG, nirK and nosZ) and denitrification potential, suggesting that manure application increased N2O emission by increasing denitrification and the population of bacteria that mediated that process.
Highlights
Nitrous oxide (N2O) accounts for nearly 8% of the warming impact of anthropogenic activities and contributes to the depletion of ozone in the stratosphere (Ravishankara, Daniel & Portmann, 2009)
Manure application can result in more N2O emissions than inorganic N fertilizers (Watanabe et al, 2014; Zhou et al, 2017), which we observed in a drip-irrigated cotton field with low soil organic carbon in arid northwestern China (Kuang et al, 2018)
Manure application significantly increased the abundances of nitrate reducer, and nirK- and nosZ-type denitrifier gene abundances and denitrifying enzyme activity (DEA)
Summary
Nitrous oxide (N2O) accounts for nearly 8% of the warming impact of anthropogenic activities and contributes to the depletion of ozone in the stratosphere (Ravishankara, Daniel & Portmann, 2009). Manure application can result in more N2O emissions than inorganic N fertilizers (Watanabe et al, 2014; Zhou et al, 2017), which we observed in a drip-irrigated cotton field with low soil organic carbon in arid northwestern China (Kuang et al, 2018). It remains unclear whether the increased emissions with manure are linked with changes in the microbial community, especially those involved in the processes of nitrification and denitrification. A recent study of fertilized subtropical forest soils in southern China found that soil factors such as NH4+ concentration and pH-controlled nitrification and denitrification activities, rather than the abundance and community structure of N-cycling prokaryotes (Tang et al, 2019)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
