南亚热带森林土壤有效氮含量及其对模拟氮沉降增加的初期响应

The short-term responses of soil available nitrogen of Dinghushan forests to simulated N deposition in subtropical China

研究了南亚热带主要森林类型 (马尾松林、混交林和季风常绿阔叶林 )土壤有效氮含量对模拟氮沉降的初期响应。结果显示 :(1)马尾松林、混交林和阔叶林 0～ 10 cm和 10～ 2 0 cm两个土层有效氮 (铵态氮 +硝态氮 )含量总平均分别为 6 .2 4、6 .2 2和14 .77m g/kg,其中铵态氮占 4 5 .3%、4 8.7%和 14 .5 %。 (2 )外加氮处理使 3个森林两个土层的有效氮含量都在增加 ,但其影响程度取决于土层、氮处理水平、氮处理时间和森林类型。总体而言 ,0～ 10 cm土层略比 10～ 2 0 cm土层敏感 ;氮处理水平越高土壤有效氮增加越多 ;外加氮处理时间越长 ,处理样方与对照样方的差距越大 ;

The short-term responses of soil available nitrogen (N) to simulated N deposition were studied in subtropical China in three representative forest types of the Dinghushan Biosphere Reserve: a pine (Pinus massoniana) forest, a pine and broadleaf mixed forest, and a monsoon evergreen broadleaf forest. Dissolved NH_4NO_3 was sprayed monthly onto the forest floor of 10 m×20 m plots as equal applications over the whole year to simulate elevated N deposition. Four treatments were established within the broadleaf stand: Control (0 kg N/(hm^(2)·a)), Low N (50 kg N/(hm^(2)·a)), Medium N (100 kg N/(hm^(2)·a)) and High N (150 kg N/(hm^(2)·a)), but only three treatments (Control, Low N, and Medium N), within the pine and the mixed stand; all in three replicates. N additions began in July 2003, and soil samples were obtained every month approx. a month after the latest N addition and analyzed for extractable NH^+_4-N and NO^-_3-N. Total means of soil available nitrogen in two depths (0~10 cm and 10~20cm) of the control plots were 6.2, 6.2 and 14.8 mg/kg with 45, 49% and 15% as NH^+_4-N form for the pine, mixed and broadleaf stand, respectively. The soil N availability increased after N additions for both soil depths in all stands, and increased with N addition level. However, the magnitude of responses varied depending on forest, soil depth and treatment time. The responses to N addition in the broadleaf stand where N is relative abundant were not as strong as in the pine and mixed stand where N is short supply. The response was slightly stronger at 0~10cm depth than at 10~20cm depth. The difference in soil available N between N addition plots and control plots increased with experimental time.