Results
A Field Experiment for N and P Impacts on
CH4Uptake
The field experiment showed that the N-only and concurrent N + P
additions treatments significantly suppressed CH4 uptake
over the entire duration of the experiment (2013-2016, Fig.
1a ). Suppression of CH4 oxidation by N addition and N +
P additions amounted to -16.3% (p < 0.01) and -7.9% (p =
0.04) relative to the control plots in 2013, -7.8% (p<0.01)
and -1.8% (p=0.10) in 2014, -12.3% (p<0.01) and -6.6%
(p<0.01) in 2015, and -18.3% (p<0.01) and -12.5%
(p<0.01) in 2016, respectively (Fig. 1d ). Over the
study period, the average annual CH4 uptake rates were
2.94 ± 0.07 kg C-CH4 ha-1 in control
plots, 2.54 ± 0.04 kg C-CH4 ha-1 in N
addition plots, and 2.73 ± 0.06 kg C-CH4ha-1 in N + P addition plots (Fig. 1a ). In
comparison with the ambient treatment, the P-only treatment slightly and
not statistically significantly stimulated CH4 uptake
throughout the experiment: +7.4% (p = 0.12) in 2013, +4.0% (p = 0.09)
in 2014, +1.2% (p = 0.2) in 2015, and +2.3% (p = 0.16) in 2016,
respectively (Fig. 1d ). Overall, P addition alone did thus not
affect CH4 uptake, N addition alone suppressed
CH4 uptake, and concurrent N + P additions suppressed
CH4 uptake to a lower degree, suggesting that P addition
alleviates the N suppression of CH4 uptake in semiarid
grasslands (Figs. 1a and 1d ).