Seedlings of Alnus nepalensis,a common tree species for timber production in subtropical area of Yunna were selected as study objects.Four levels of simulated nitrogen deposition (5,10,15 and 30 g · m-2 · a-1) and a control (0 g · m-2 · a-1) were set up to study their effects on the growth,biomass allocation,and the relationship between size and number of twig-leaf.The results showed that compared with the control,lower nitrogen treatment (5 g · m-2 · a-1)promoted the growth of A.nepalensis seedlings,while moderate (15 g · m-2 · a-1) and high (30 g · m-2 · a-1) levels of nitrogen inhibited the development of the seedlings.Total individual biomass decreased with the increase of nitrogen treatment after 12 month treatment.Leaf weight ratio,branch weight ratio and root crown ratio presented the increase trends.The import of nitrogen dopistion could change biomass allocation and the traits of twigs and leaf in the different organs of the seedlings.Cross-sectional area of twigs,total leaf area,twig length and leaf number decreased with the increase of nitrogen doposition treatment.Small cross-sectional area of twigs could suport more total leaf area and leaf number in the high level of nitrogen treatment.%选择云南省南亚热带地区常见的用材树种旱冬瓜幼苗,设置4种模拟氮沉降水平(5、10、15、30g·m 2·a-1)以及1组对照控制试验,研究模拟氮沉降增加对其生长效应和枝叶的大小与数量关系的影响.结果表明:与对照处理组的旱冬瓜幼苗株高和地径比较,在低氮水平处理(5g·m-2·a-1)下极大促进了幼苗的生长,而中氮(15 g·m 2·a-1)和高氮(30 g·m-2·a-1)水平处理组的旱冬瓜幼苗生长逐渐受到抑制,原因是由于氮输入的增加以及旱冬瓜的根瘤菌具有明显的固氮作用.同时,经过12个月的处理,旱冬瓜幼苗的全株生物量随氮沉降处理水平的增加而降低,而叶重比、根重比和根冠比则呈增加趋势,氮沉降的输入改变了不同器官在全袜生物量的分配.模拟氮沉降的不同处理水平影响了旱冬瓜幼苗的枝叶构建特征,表现为茎截面积、总叶面积、枝长度和叶片数也随氮沉降处理的增加而降低,高氮处理下的旱冬瓜在较小的单位茎截面积上会支撑更多的叶面积,在较小的枝长度可以支撑较多的叶片数.
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