Tree growth on weathered soils in lowland tropical forests is limited by low phosphorous (P) availability. However, nutrient manupulation experiments do not always increase the P content in these trees, which raises the question whether trees are taking up added P. In French Guianese lowland rainforest, we measured changes in nitrogen (N) and P availability before and up to two months after N and P fertilizer addition, in soils with intact root systems and in soils where roots and mycorrhizal fungi were excluded by root exclusion cylinders. When the root system was excluded, P addition increased P availability to a much greater extent and for a longer time than in soils with an intact root system. Soil N dynamics were unaffected by root presence/absence. These results indicate rapid P uptake, but not N uptake, by tree roots, suggesting a very effective P acquisition process in these lowland rainforests.

低地热带森林中风化土壤上的树木生长受到磷（P）利用率低的限制。但是，养分操纵试验并不总是增加这些树木中的P含量，这引发了树木是否吸收了P的问题。在法国圭亚那低地雨林中，我们测量了氮素（N）和磷的有效性在施用完氮和磷肥的几个月后，在根系完好的土壤中以及在根部和根部隔离柱排除了根和菌根真菌的土壤中。当根系被排除在外时，与根系完整的土壤相比，磷的添加在更大的程度上和更长的时间内增加了磷的有效性。土壤氮素动力学不受根系存在与否的影响。这些结果表明树木的根部快速吸收P，但不吸收N，