Understanding how nitrogen (N) availability interacts with soil acidity and phosphorus (P) availability to affect soil-atmosphere exchanges in CO2, CH4 and N2O in forest ecosystems is important for understanding the mechanisms driving ecosystem responses to enhanced N deposition. Here, we conducted an experiment with N, P and acid (H) addition in a mixed forest in subtropical China to investigate how acid and P addition affects CO2, CH4 and N2O exchange under N addition. Our results showed that soil -N and -N increased after N addition, but CO2 emissions in N addition plots remained unaffected. CH4 uptake in N-, P-, NP-, NH- and NPH-addition plots were reduced by 21.1%, 15.7%, 39.1%, 26.6%, and 28.4%, respectively. CH4 uptake in NP-addition plots were lower compared to N-addition and P-addition plots, indicating that N and P addition had an additive effect on inhibiting CH4 uptake. N2O emission in N-, NP-, NH- and NPH-addition plots increased by 158.6%, 176.0%, 117.2%, and 91.8%, respectively. N2O emissions in NPH-addition plots were lower compared to NP-addition plots while showed no difference between N-addition and NH-addition plots. This suggests that only under P rich conditions, acid addition would greatly mitigate N2O emissions under N addition. Our results demonstrate that for N and P co-limited forest ecosystems with acidic soils, low P availability constrains the inhibition of soil CH4 uptake by N deposition. When P availability is low, a weak soil acidation induced by N deposition may have less influence on the stimulation of N2O emissions by N deposition.
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Vol. 8 • No. 2