Conifers are, for the most part, competitively excluded from tropical rainforests by angiosperms. Where they do occur, conifers often occupy sites that are relatively infertile. To gain insight into the physiological mechanisms by which angiosperms outcompete conifers in more productive sites, we grew seedlings of a tropical conifer (Podocarpus guatemalensis Standley) and an angiosperm pioneer (Ficus insipida Willd.) with and without added nutrients, supplied in the form of a slow-release fertilizer. At the conclusion of the experiment, the dry mass of P. guatemalensis seedlings in fertilized soil was approximately twofold larger than that of seedlings in unfertilized soil; on the other hand, the dry mass of F. insipida seedlings in fertilized soil was ~20-fold larger than seedlings in unfertilized soil. The higher relative growth rate of F. insipida was associated with a larger leaf area ratio and a higher photosynthetic rate per unit leaf area. Higher overall photosynthetic rates in F. insipida were associated with an approximately fivefold larger stomatal conductance than in P. guatemalensis. We surmise that a higher whole-plant hydraulic conductance in the vessel bearing angiosperm F. insipida enabled higher leaf area ratio and higher stomatal conductance per unit leaf area than in the tracheid bearing P. guatemalensis, which enabled F. insipida to capitalize on increased photosynthetic capacity driven by higher nitrogen availability in fertilized soil.

中文翻译：

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为什么热带针叶树在肥沃的土壤中处于不利地位？危地马拉罗汉松与被子植物先锋榕（Ficus insipida）的比较。

在大多数情况下，被子植物将针叶树排除在热带雨林之外。确实发生针叶树的地方，针叶树经常占据相对不育的位置。为了深入了解被子植物在更富生产力的地区竞争胜过针叶树的生理机制，我们种植了热带针叶树（Podocarpus guatemalensis Standley）和被子植物先驱（Ficus insipida Willd。）的幼苗，有或没有添加营养素，均以缓释肥料。在实验结束时，肥料中的危地马拉幼苗的干质量约为未肥料中的幼苗的两倍。另一方面，施肥土壤中F. insipida幼苗的干燥质量是未施肥土壤中的F. insipida幼苗的约20倍。F的相对增长率较高。烟叶与较大的叶面积比和较高的单位叶面积光合速率有关。与瓜果假单胞菌相比，F。insipida的整体光合速率较高，其气孔导度大约高五倍。我们推测，被子植物F. insipida的容器中较高的全株水力传导率使叶片面积比和单位叶面积的气孔导度比在气管中的危地马拉P. guatemalensis高，这使得Insipida可以利用增加的光合作用。施肥土壤中较高的氮利用率驱动着土壤的生产能力。与危地马拉假单胞菌相比，稻纵卷叶st的气孔导度大约高五倍。我们推测，被子植物F. insipida的容器中较高的全株水力传导率使叶片面积比和单位叶面积的气孔导度比在气管中的危地马拉假单胞菌更高，这使得Insipida可以利用增加的光合作用。施肥土壤中较高的氮利用率驱动着土壤的生产能力。与危地马拉假单胞菌相比，稻纵卷叶st的气孔导度大约高五倍。我们推测，被子植物F. insipida的容器中较高的全株水力传导率使叶片面积比和单位叶面积的气孔导度比在气管中的危地马拉假单胞菌更高，这使得Insipida可以利用增加的光合作用。施肥土壤中较高的氮利用率驱动着土壤的生产能力。