鼎湖山主要森林类型植物胸径生长对氮沉降增加的初期响应

Response of Diameter at Breast Height Increment to N Additions in Forests of Dinghushan Biosphere Reserve

在林地分别喷加0、50、100和150kgNhm-2a-1,研究鼎湖山马尾松林、马尾松荷木混交林和季风常绿阔叶林乔木层植物胸径生长(年增长率)对增施氮的响应。结果表明,不喷加N,马尾松林、混交林和阔叶林胸径年增长率分别为4.84%、4.09%和2.99%;外加氮对植物胸径生长的影响因森林类型和植物种而异。马尾松林和混交林,低氮处理(喷加50kgNhm-2a-1)没有对胸径生长产生明显影响,中氮处理(喷加100kgNhm-2a-1)则分别增加了77.8%和105.6%。外加氮处理均使阔叶林胸径年增长率下降,低氮、中氮和高氮处理(喷加150kgNhm-2a-1)分别比对照(不喷N)低36.8%、28.5%和41.0%。这表明外加氮处理促进马尾松生长,但抑制大多数阔叶树种生长。

The responses of diameter at breast height (DBH) in tree layer to nitrogen (N) additions were studied in three representative forest types in Dinghushan Biosphere Reserve: a pine (Pinus massoniana) forest, a pine- broadleaved mixed forest, and a broadleaved forest. Dissolved NH4NO3 was sprayed monthly with equal appli- cations dose onto the forest floor of 10 m×20 m plots within a year to simulated elevated N deposition. Four treat- ments were established in the broadleaved forest: control, low N (50 kg N hm-2a-1), moderate N (100 kg N hm-2a-1) and high N (150 kg N hm-2a-1), and three treatments (control, low N and moderate N), in mixed and pine forests. All the treatments were in three replicates. Annual increment rates of DBH in control plots were estimated to be 4.84%, 4.09% and 2.99% for the pine, mixed and broadleaved forests, respectively. After treatment with N additions for one year, in the pine and mixed forest, the DBH increment rate in low N plots was similar to that in the control, while in moderate N plots the increment rates in pine forest and mixed forest were by 77.8% and 105.6%, respectively, higher than those of the control. In contrast, in the broadleaved forest, all N addition treatments decreased the tree growth, though the treatment effect was not significant, and the increment rates in the low, moderate and high N plots were by 36.8%, 28.5% and 41.0%, respectively, lower as compared to the control. The effects of N addition on tree growth different in species. N additions stimulated the growth of Pinus massoniana both in pine forest and mixed forest, but decreased that of most broadleaved species in all the three forests.