通过3个水平野外氮添加控制试验(0、40、120 kg N·hm^(-2)·a^(-1)),研究氮添加对亚热带湿地松林土壤水解酶和氧化酶活性的影响.结果表明:氮添加显著抑制了土壤有机质中碳、氮、磷水解酶和氧化酶的活性,导致β-1,4-葡糖苷酶(BG)、纤维素二糖水解酶(CBH)、β-1,4-乙酰基-葡糖胺糖苷酶(NAG)、过氧化物酶(PER)活性下降16.5%~51.1%,并且高水平氮添加对酶活性抑制效果更明显;氮添加导致α-1,4-葡糖苷酶(aG)、β-1,4-木糖苷酶(BX)、酸性磷酸酶(AP)、多酚氧化酶(PPO)活性降低14.5%~38.6%,不同水平氮添加处理间差异不显著.土壤酶活性存在明显的季节性差异,BG、NAG、BX、CBH、AP、PPO活性表现为3月>6月>10月,aG、PER活性表现为10月>3月>6月.多数土壤水解酶和氧化酶与pH呈显著正相关,与NO_3^--N含量呈显著负相关,表明氮添加导致p H降低和土壤中硝化作用增强,抑制了土壤水解酶和氧化酶活性.氮添加不利于亚热带土壤有机质的矿化和周转,并且随着氮添加量的增加,效果更明显.
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.
