Environmental Studies Program, University of Oregon, Eugene, OR, USA.
Department of Geography, University of Oregon, Eugene, OR, USA.
Nat Commun. 2021 Jan 4;12(1):127. doi: 10.1038/s41467-020-20184-2.
Amazonian Dark Earths (ADEs) are unusually fertile soils characterised by elevated concentrations of microscopic charcoal particles, which confer their distinctive colouration. Frequent occurrences of pre-Columbian artefacts at ADE sites led to their ubiquitous classification as Anthrosols (soils of anthropic origin). However, it remains unclear how indigenous peoples created areas of high fertility in one of the most nutrient-impoverished environments on Earth. Here, we report new data from a well-studied ADE site in the Brazilian Amazon, which compel us to reconsider its anthropic origin. The amounts of phosphorus and calcium-two of the least abundant macronutrients in the region-are orders of magnitude higher in ADE profiles than in the surrounding soil. The elevated levels of phosphorus and calcium, which are often interpreted as evidence of human activity at other sites, correlate spatially with trace elements that indicate exogenous mineral sources rather than in situ deposition. Stable isotope ratios of neodymium, strontium, and radiocarbon activity of microcharcoal particles also indicate exogenous inputs from alluvial deposition of carbon and mineral elements to ADE profiles, beginning several thousands of years before the earliest evidence of soil management for plant cultivation in the region. Our data suggest that indigenous peoples harnessed natural processes of landscape formation, which led to the unique properties of ADEs, but were not responsible for their genesis. If corroborated elsewhere, this hypothesis would transform our understanding of human influence in Amazonia, opening new frontiers for the sustainable use of tropical landscapes going forward.
亚马逊黑土（ADEs）是一种异常肥沃的土壤，其特征是含有大量微观炭粒，这赋予了它们独特的颜色。在 ADE 地点频繁发现前哥伦布时期的文物，导致它们被普遍归类为Anthrosols（人为起源的土壤）。然而，人们仍然不清楚土著人民是如何在地球上营养最贫瘠的环境之一创造出高肥力地区的。在这里，我们报告了来自巴西亚马逊一个经过充分研究的 ADE 地点的新数据，这些数据迫使我们重新考虑其人为起源。ADE 剖面中的磷和钙（该地区两种最稀缺的大量营养元素）的含量比周围土壤高出几个数量级。在其他地点被解释为人类活动证据的磷和钙的升高水平，与指示外来矿物来源而不是原地沉积的微量元素在空间上相关。微炭颗粒的钕、锶和放射性碳稳定同位素比值也表明，碳和矿物质元素的冲积沉积从几千年前就开始向 ADE 剖面输入，早于该地区开始进行植物种植的土壤管理的最早证据。我们的数据表明，土著人民利用了景观形成的自然过程，这导致了 ADE 的独特性质，但他们并不是其起源的原因。如果在其他地方得到证实，这一假设将改变我们对亚马逊地区人类影响的理解，为未来热带景观的可持续利用开辟新的前沿。
