鼎湖山主要森林土壤N_2O排放及其对模拟N沉降的响应

SOIL N_2O EMISSION AND ITS RESPONSE TO SIMULATED N DEPOSITION IN THE MAIN FORESTS OF DINGHUSHAN IN SUBTROPICAL CHINA

研究了鼎湖山生物圈保护区马尾松（Pinus massoniana）林、混交林和季风常绿阔叶林（季风林）土壤N2O排放特征及其对氮沉降增加的响应.在1999～2002年期间,3种森林土壤N2O排放速率均表现明显的季节性变化特点,但这种季节性变化因年份和森林类型不同而异,总的来说,3种森林土壤N2O排放速率呈现夏秋季较高而冬春季较低的变化.土壤N2O排放速率在3年观测期间的平均值分别为（g·hm^-2·d^-1）：14.2±3.1（季风林）,5.8±0.9（混交林）和5.1±0.9（马尾松林）.土壤N2O排放速率与土壤温度之间在季风林呈现显著的指数正相关关系,但在混交林和马尾松林中它们之间的关系则均不明显.经3个月的模拟氮沉降试验后,氮沉降增加对季风林和马尾松林土壤N2O的排放均具有明显的促进作用,且这种促进作用随氮沉降水平的升高而增强,但对混交林土壤N2O排放的影响则不明显.

Background and Aims Most studies of the consequences of enhanced nitrogen deposition on sources and sinks of greenhouse gases have been performed in temperate ecosystems. Little information is available about greenhouse gases and responses to atmospheric nitrogen deposition in subtropical and tropical forests, especially in the forests of China. The objective of this study was to determine soil N2O emission and its response to simulated N deposition in pine forest （PF）, pine- broadleaf mixed forest （MF）, and monsoon evergreen broadleaf forest （MEBF） of Dinghushan in subtropical China. Methods Four N addition treatments （in three replicates） were established in MEBF： Control, Low N （50 kg N·hm^-2·a^-1）, Medium N （100 kg N·hm^-2·a^-1） and High N （150 kg N·hm^-2·a^-1）, and three treatments were established in MF and PF （Control, Low N and Medium N）. Key Results The effects of nitrogen addition on soil N20 emission differed by forest type. In MF, no significant differences were found among the three treatments after 3 months. In PF, however, soil N2O emission rate was significantly higher in Medium plots than that in Low or Control plots, which exhibited no significant difference. In MEBF, soil N2O emission rate was highest in High N plots and significantly higher in Medium plots than in Low or Control plots, which exhibited no significant difference. Conclusions This study suggests that nitrogen addition significantly stimulated soil N2O emission rates in both MEBF and PF, and its effect generally increased with the levels of nitrogen addition, but there was no such significant effect in MF.