Responses of N2O flux and functional genes to
nitrogen addition and altered precipitation
N2O emissions showed a significant seasonal dynamic,
with the maximum flux appearing in August (Figure 2A). Although the
average flux was relatively small,
the
alpine steppe
presented
as the source of N2O (F > 0) during
the growing season under different treatment conditions
(Figure
2B). The addition of N resulted in a significant increase in
N2O emissions (317%) (Figure 2B-C). However,
N2O
emissions were not significantly influenced by altered precipitation or
the interaction between N addition and precipitation changes (Figure
2B).
To
a certain extent, the coupling of N and water alleviated the effect of N
input on N2O emissions (178% and 100% vs 317%)
(Figure 2B-C). Similarly, N2O flux during the emission
peak was only affected by N addition (Figure 2D).
The amo A gene abundance of the nitrifier AOA was significantly
affected by both N supply and precipitation changes (Figure 3A).
However, the AOB amo A gene
abundance was significantly elevated only by N supply (Figure 3B).
Although the denitrifier nirS and nirK genes regulate the
same step in denitrification (nitrite reduction:
NO2−→
NO), only the nirS gene
abundance was significantly affected by the interaction of N addition
and precipitation changes (Figure 3C).
The
abundance of the nirK gene did not significantly differ among the
treatments (Figure 2D). The abundance of the nosZ gene was
reduced under N addition, and altered precipitation did not
significantly affect the nosZ gene abundance (Figure 3E).