Tropical forests are generally considered to stand upon nutrient-poor soils, but soil nutrient concentrations and availabilities can vary greatly at local scale due to topographic effects on erosion and water drainage. In this study we physically and chemically characterised the soils of 12 study plots situated along a catena with a shallow slope in a tropical rainforest in French Guiana both during the wet and the dry season to evaluate seasonal differences. Soils along the catena were all Acrisols, but differed strongly in their water drainage flux. Over time, this differential drainage has led to differences in soil texture and mineral composition, affecting the adsorption of various nutrients, most importantly phosphorus. The more clayey soils situated on the slope of the catena had higher total concentrations of carbon, nitrogen, phosphorus and several micronutrients, while extractable nutrient concentrations were highest in the sandiest soils situated at the bottom of the catena. We found that carbon, nitrogen and extractable nutrients all varied seasonally, especially in the surface soil layer. These results are interesting because they show that, even at the local scale, small differences in topography can lead to large heterogeneity in nutrient concentrations, which can have large impacts on plant and microbial community organisation at the landscape level.

中文翻译：

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法属圭亚那帕拉库浅层土壤养分变化

热带森林通常被认为位于营养贫乏的土壤上，但由于地形对侵蚀和排水的影响，土壤养分浓度和可用性在当地范围内可能会有很大差异。在这项研究中，我们在湿季和旱季对法属圭亚那热带雨林中的 12 个研究地块的土壤进行了物理和化学特征分析，以评估季节性差异。沿链的土壤都是 Acrisols，但它们的排水通量差异很大。随着时间的推移，这种差异排水导致土壤质地和矿物质成分的差异，影响了各种养分的吸收，最重要的是磷。位于链带斜坡上的粘土越多，碳、氮、磷和几种微量营养素，而位于链底部的最沙质土壤中可提取的营养素浓度最高。我们发现碳、氮和可提取的养分都有季节性变化，尤其是在表层土壤中。这些结果很有趣，因为它们表明，即使在局部尺度上，地形的微小差异也会导致养分浓度的巨大异质性，这会对景观水平的植物和微生物群落组织产生很大影响。