中文摘要：

理解土壤可利用性氮（N）如何与土壤酸化和可利用性磷（P）共同作用影响土壤-大气界面CO_2、CH_4和N_2O气体交换,对于揭示生态系统对氮沉降增加的响应机制尤为重要。本研究在中国亚热带地区混交林中设置了N、P和酸添加实验以理清在N添加下酸和P添加如何影响CO_2、CH_4和N_2O气体交换。结果表明,（1）N添加显著增加了土壤铵态氮和硝态氮,对CO_2释放无影响;（2）N、P、N＋P和N^＋P^＋酸分别降低了21.1%、15.7%、39.1%、26.6%和28.4%的CH_4;相比于N、P单独添加,NP共同添加降低了CH_4吸收,表明N添加和P添加在抑制CH_4吸收上具有加和效应;（3）N、N＋P、N＋酸和N^＋P^＋酸分别增加了158.6%、176.0%、117.2%和91.8%的N_2O释放;N_2O释放在N^＋P^＋酸处理中显著低于N＋P处理,与N添加和N＋酸添加无显著差异,表明在N添加下,仅P丰富的条件下,酸添加才能够缓解N_2O释放。我们的结果证实,在N和P共同限制的酸性土壤森林生态系统,低P将会抑制N沉降引起的土壤CH_4吸收。低P时,N沉降引起的土壤酸化与其引发的N_2O释放无关。

英文摘要：

Understanding how nitrogen（N） availability interacts with soil acidity and phosphorus（P） availability to affect soil-atmosphere exchanges in CO_2, CH_4 and N_2O 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 CO_2, CH_4 and N_2O exchange under N addition. Our results showed that soil NH4^＋-N and NO3^--N increased after N addition, but CO_2 emissions in N addition plots remained unaffected. CH_4 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. CH_4 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 CH_4 uptake. N_2O emission in N–, NP–, NH– and NPH–addition plots increased by 158.6%, 176.0%, 117.2%, and 91.8%, respectively. N_2O 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 N_2O 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 CH_4 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 N_2O emissions by N deposition.