中文摘要：

为理解氮沉降持续增加对次生林生态系统碳循环相关过程的影响，2013年5月开始对瓦屋山常绿阔叶次生林进行模拟氮沉降试验，氮沉降水平分别为对照（CK，0 kg hm-2 a-1）、低氮（LN，50 kg hm-2 a-1）和高氮（HN，150 kg hm-2 a-1）. 于2013年9月至2014年8月，每月下旬采用LI-8100开路式土壤碳通量测量系统测定土壤呼吸速率. 结果显示：瓦屋山常绿阔叶次生林土壤呼吸速率季节变化明显，7月最高（2.77 mol m2 s1），1月最低（0.46 mol m2 s1）. 该次生林累积土壤碳排放量为591 g m2 a1. 土壤呼吸与土壤温度呈极显著（P 〈 0.01）正指数相关，与土壤湿度无显著关系（P 〉 0.05）. 模拟氮沉降显著（P = 0.027）抑制了土壤呼吸，高氮处理年均土壤呼吸速率较对照极显著（P 〈 0.01）下降31.4%. 基于土壤温度的土壤呼吸Q10值为2.63，低氮和高氮处理Q10值分别较对照增加16%和33%. 综上所述，在该生态系统土壤氮含量较高的背景下，模拟氮沉降可能加剧了土壤碳限制，通过减缓植物根系生长和降低土壤微生物生物量抑制了土壤CO2排放.

英文摘要：

In order to understand the effect of nitrogen deposition on forest ecosystem carbon cycle, this study aimed to reveal the soil respiration response mode to nitrogen deposition and its mechanism in a secondary evergreen broad-leaved forest in Wawushan Mountain. From May 2013, a field experiment including three treatments was conducted in this secondary forest, i. e.,no N addition （control）, N addition at 50 kg hm-2 a-1 （low-N）, and at 150 kg hm-2 a-1 （high-N）. From September 2013 to August 2014, we investigated the soil respiration rate with LI-8100 at the end of each month. The results showed an obvious seasonal change in soil respiration rate of the secondary forest, with the maximum （2.77 mol·m2·s1） in July and the minimum （0.46 mol·m2·s1） in January. In the secondary forest, cumulative soil carbon emissions was 591 g m2 a1. Soil respiration rate had significant positive exponential relationships with soil temperature, but no significant relationships with soil moisture. Soil respiration was significantly suppressed by simulated nitrogen deposition, and the annual soil respiration rate of high-N was 31.4% significantly lower compared with the control. The soil respiration Q10 value calculated from soil temperature was 2.63, and that of low-N and high-N were 16% and 33% respectively higher than the control. Due to the high nitrogen content in soil, simulated nitrogen deposition may accentuate soil carbon limitation, slow down the growth of plant roots and reduce soil microbial biomass, eventually inhibit soil CO2 emission.