Statistical analyses
Before statistical analysis, we examined whether the data conformed to a
normal distribution (Shapiro–Wilk test) and tested for homogeneity of
variance (Levene’s test).
We
conducted data analysis according to the following four steps.
First,
a Two-way Analysis of variance (ANOVA) was used to examine the effects
of N addition, altered precipitation, and their interaction on the
following: soil abiotic parameters (soil temperature, moisture, pH,
NH4+-N, and
NO3−-N);
plant properties (aboveground and belowground biomass);
N2O flux (emission peak); and the functional gene
abundance related to nitrification (AOA, AOB) and denitrification
(nirS , nirK , andnos Z).
Second,
a repeated-measures ANOVA was performed to assess the
effects
of treatments
on
N2O
flux
during the growing season. Significant differences of the
above-mentioned parameters were assessed using post-hoc tests (Duncan’s
test at P < 0.05). Third, linear regression analysis
was used to evaluate the relationships among N2O flux
and soil abiotic factors and plant properties.
Finally,
a Pearson correlation analysis was used to investigate the correlation
between functional gene abundances and N2O flux. These
statistical analyses were carried out in SPSS version 21.0 (SPSS,
Chicago, IL, U.S.A.) and were visualized using Sigmaplot 12.5 software
(Systat Software Corporation, U.S.A.).