短期氮添加对东灵山三种森林土壤呼吸的影响

Short-term effect of nitrogen addition on soil respiration of three temperate forests in Dongling Mountain

为了分析氮沉降对我国温带地区森林土壤碳循环的影响,以北京东灵山的阔叶林（辽东栎林）和针叶林（华北落叶松林和油松林）为研究对象,通过模拟氮沉降的方式（10g N·m-2·a-1,大约5倍于大气氮沉降速率）,探讨了不同温带森林土壤呼吸对氮沉降的短期响应。结果表明：短期氮添加降低了阔叶林土壤呼吸速率,而提高了针叶林土壤呼吸速率,但其短期效应未达到显著性水平。不同森林类型间,土壤呼吸速率（P〈0.001）和生长季土壤呼吸释放总量（P〈0.001）均存在显著差异,整体表现为：辽东栎林〉油松林〉华北落叶松林,土壤温度是引起不同森林类型间土壤呼吸差异的主要因素。温度-水分双因素模型可以较好地模拟野外条件下3种森林类型土壤呼吸与温度和水分间的关系,解释率约为47%~87%。此外,氮添加可以改变土壤呼吸对温度和水分变化的响应：氮添加后在较高温度且较低水分情况下,土壤呼吸速率明显上升,此时土壤呼吸对温度变化更加敏感。实验结果揭示了氮沉降对我国温带地区不同森林类型土壤呼吸的影响,但其复杂的影响机制仍有待进一步研究。

To investigate the effect of N deposition on soil respiration of temperate forests, a simulated atmospheric nitrogen （N） deposition experiment was conducted in three typical temper- ate forests in Dongling Mountain in Beijing. The three forests included oak forest （broadleaf for- est）, larch forest and pine forest （coniferous forest）. In each forest, we set control and N addi- tion treatments （10 g N · m-2 · a-1, five times of current atmospheric N deposition） and four replicates （15 m × 15 m）. N addition （NH4NO3 ） and soil respiration measurement were con- ducted in growing season. The results showed that N addition decreased the soil respiration rate of broadleaf forest but enhanced that in coniferous forest. Under the N enriched condition, the accu- mulation emission of soil respiration during the growing season decreased by 6.13 g C · m-2 in oak forest while increased by 1.78 g C · m-2 and 5.64 g C · m-2 in larch and pine forests, re- spectively. However, the short-term effect of N addition was not significant among three temperate forests. Moreover, soil respiration rate （P〈0.001） and the accumulation emission of soil respira- tion （P〈0.001） in growing season among different forests varied significantly in the order of oak forest 〉 pine forest 〉 larch forest. Soil temperature was the key factor regulating soil respiration in the control and N addition treatments, which resulted in an apparent seasonal variation of soil res- piration. The two-factor model, involving soil temperature and moisture, well fitted the variation of soil respiration in response to the temperature and moisture in the three temperate forests, and explained the 47%-87% variation of soil respiration. Furthermore, N addition regulated to some extent the response of soil respiration to soil temperature and moisture, and soil respiration in- creased faster and was more sensitive under conditions of relatively higher temperature and lower moisture under N addition. These findings revealed the short-term effects of N addition on soil respiration in different temperate forests in North China, however, its underlying mechanisms is still unclear.