不同氮磷添加浓度对豆科3种树木幼苗生长及生物量分配的影响

选取海南尖峰岭热带山地雨林中不同功能类群的豆科树木幼苗（代表低氮需求的长脐红豆Ormosia balansae Drake、中氮需求的荔枝叶红豆Ormosia semicastrata Hance f. litchifolia How和高氮需求的猴耳环Archidendron clypearia（Jack）I.C.Nielsen）为对象，设置5个浓度梯度的氮（N）添加和2个浓度梯度的磷（P）添加养分控制实验，研究苗木的生长表现。结果显示：（1）氮添加条件下，3个树种幼苗的苗高、总叶面积、根长、根表面积、生物量5个指标对中高浓度氮添加的敏感性大小均为长脐红豆 > 猴耳环 > 荔枝叶红豆；其中，叶总面积对氮肥浓度变化的响应最敏感，长脐红豆的根长、根表面积以及猴耳环根长的响应敏感性次之。（2）长脐红豆和猴耳环幼苗的根冠比受氮肥添加浓度的影响不显著；荔枝叶红豆幼苗的根冠比则随氮肥添加浓度的升高而增大，这种适应策略反映出荔枝叶红豆幼苗对添加中高浓度氮肥有较强的耐受能力。（3）磷添加条件下，长脐红豆和猴耳环幼苗的生长速率为低磷>高磷，表明这2个树种在幼苗阶段为低氮、低磷需求；荔枝叶红豆在低氮处理下的生长速率为高磷>低磷，表明该树种幼苗阶段为低氮、高磷需求。

Effects of varied soil nitrogen and phosphorus concentrations on the growth and biomass allocation of three leguminous tree seedlings

We selected three different functional groups of leguminous tree seedlings from a 60 hm² sample plot of tropical mountain rainforest in Jianfengling, Hainan, China, as the study objects. The three leguminous trees included Ormosia balansae Drake, Ormosia semicastrata Hance f. litchifolia How, and Archidendron clypearia (Jack) I. C. Nielsen, with low, medium, and high nitrogen (N) demands, respectively. We conducted a soil nutrient control experiment in a greenhouse and compared growth performance of the three leguminous plant seedlings under five N and two phosphorus (P) addition concentration gradients. Results showed that:(1) Under N enrichment, the sensitivities of the five indicators, i.e., seedling height, total leaf area, total root length, root surface area, and biomass, to medium and high N addition were in the order of O. balansae > A. clypearia > O. semicastrata f. litchifolia. Additionally, total leaf area was the most sensitive index to changes in soil N concentration, followed by total root length and root surface area of O. semicastrata f. litchifolia seedlings as well as total root length of A. clypearia seedlings. (2) The root shoot ratio of O. semicastrata f. litchifolia and A. clypearia seedlings was relatively unaffected by N addition. In contrast, the root shoot ratio of O. semicastrata f. litchifolia seedlings increased markedly with the increase in N concentration, implying that O.semicastrata f. litchifolia had a greater tolerance to medium and high soil N concentrations. (3) Under P enrichment, O. balansae and A. clypearia seedlings showed a greater growth rate under low than high P addition, indicating low N and low P demand for these two species at the seedling stage. However, O. semicastrata f. litchifolia seedlings grew faster with high P and low N treatment, thus suggesting low N and high P demand at the seedling stage.