中文摘要：

为阐明南亚热带4个主要树种——海南红豆（Ormosia pinnata）、马占相思（Acacia mangium）、木荷（Schima superba）和马尾松（Pinus massoniana）幼苗生长对不同氮添加量和添加方式的响应差异,进行了幼苗模拟氮添加实验。实验设置3个氮添加水平（对照：背景大气氮沉降量5.6 g N·m–2·a–1,中氮：15.6 g N·m–2·a–1,高氮：20.6 g N·m–2·a–1）,每个水平分两种添加方式（幼苗冠层施氮和土壤表层施氮）,共6个处理：（1）土壤对照（S-CK）;（2）土壤中氮（S-MN）;（3）土壤高氮（S-HN）;（4）冠层对照（C-CK）;（5）冠层中氮（C-MN）;（6）冠层高氮（C-HN）,每个处理设置6个重复。研究结果表明：不同氮添加量下,土壤施氮和冠层施氮对植物幼苗生长的影响不同,氮添加量、氮添加方式和物种3个因子之间存在显著的交互效应。与对照相比,S-MN增加了马占相思和木荷幼苗的生物量,降低了马尾松的株高和生物量,而C-MN仅增加了马占相思的生物量,对其他3个树种没有影响;S-HN增加了马占相思的生物量,显著降低了马尾松的基径、株高和生物量（p〈0.01）,C-HN增加了马占相思、木荷和马尾松的基径、株高和生物量（p〈0.01）。不同氮添加量和氮添加方式对幼苗生长的影响因物种而异,所有氮处理下海南红豆和马占相思的生长均明显快于木荷和马尾松;木荷和马尾松幼苗的生长在两种氮添加方式间差异显著,冠层施氮比土壤施氮对其幼苗生长的促进作用更大。由此可见：在氮沉降背景下,阔叶豆科植物（海南红豆、马占相思）比阔叶非豆科植物（木荷）生长快;阔叶树种（海南红豆、马占相思和木荷）比针叶树种（马尾松）生长快。在长期氮沉降环境下,不同物种生长的差异响应有可能导致亚热带森林物种组成发生变化。

英文摘要：

Aims Numerous studies have been carried out concerning the effects of atmospheric nitrogen（N） deposition on forest ecosystems. However, most of previous experiments were conducted by adding N fertilizer to the surface soil directly. Realistically simulated canopy N deposition and comparison of the effects of soil N addition and canopy N addition on ecosystems were rare. Our purpose is to better understand the effects of two N addition regimes at different N addition levels on seeding growth in major tree species of subtropical China. Methods A 2-year pot experiment was conducted, with seedlings of four species（Ormosia pinnata, Acacia mangium, Schima superba, Pinus massoniana） grown in pots subjected to treatments of three levels（ambient, medium, and high） and two regimes（in soil vs. on canopy） of N addition, specifically including S-CK（ambient N addition in soil）, S-MN（medium N addition in soil）, S-HN（high N addition in soil）, C-CK（ambient N addition on canopy）, C-MN（medium N addition on canopy）, and C-HN（high N addition on canopy）. The total amounts of added N in the three N levels were 5.6, 15.6 and 20.6 g·m–2·a–1, respectively. Tree basal diameter and tree height were measured in June and December 2012, and November 2013. All trees were harvested in November 2013, and then the biomass was calculated according to the dry-mass of roots, shoots and leaves; the root-shoot ratioswere calculated. Important findings N treatments affected seeding growth, along with significant interactive effects among N addition level, N addition regime and species. Compared to CK, S-MN stimulated the biomass in seedlings of A. mangium and S. superba, but decreased the tree height and biomass in seedlings of P. massoniana; C-MN increased the biomass in seedlings of A. mangium; S-HN promoted the biomass in seedlings of A. mangium, but significantly decreased the biomass, basal diameter and tree height in seedlings of P. massoniana（p 0.01）; C-HN led to the greater growth in seedlings of