In the nutrient-poor soils of the Amazon rainforest, phosphorus (P) emerges as a critical limiting factor for ecosystem productivity. Despite these limitations, the Amazon exhibits remarkable productivity that is maintained by its efficient nutrient recycling mechanisms. Central to this process is the role of organic matter, particularly its dissolved (DOM) fraction, which serves as a crucial nutrient reservoir for both plants and microorganisms. This study delves into the dynamics of nutrient-containing DOM within the soils of two contrasting rainforest ecosystems: clayey terra firme forests, known for their robust nutrient recycling and presumed P-limitation, and sandy white-sand forests, characterized by reduced nutrient recycling capacity and presumed nitrogen (N)-limitation. Utilizing ultra-high resolution mass spectrometry (HR-MS), we analyzed the molecular composition of dissolved organic nutrient species. We evidenced nutrient limitation applying innovative concepts: (1) assessing nutrient depletion in DOM via nutrient-to-carbon ratios, (2) comparing the composition of nutrient-enriched DOM pools across soil depth profiles to infer microbial nutrient processing, and (3) examining the temporal variability of nutrient-containing DOM as an indicator of nutrient uptake and production. Our results corroborate the hypothesis of P-limitation in terra firme forests, with significant processing of N-containing DOM also observed, indicating a synergistic demand for both P and N. Surprisingly, white-sand soils exhibited no signs of N-limitation but instead sulfur (S)-limitation, a novel finding for these ecosystems. This study highlights the diversity of potential nutrient limitations in the central Amazon and the importance of the bioavailable “black box” DOM for tropical nutrient cycles.

在亚马逊雨林营养贫乏的土壤中，磷 （P） 成为生态系统生产力的关键限制因素。尽管存在这些限制，亚马逊地区仍表现出卓越的生产力，这得益于其高效的养分回收机制。这个过程的核心是有机物的作用，特别是其溶解 （DOM） 部分，它是植物和微生物的重要营养库。本研究深入探讨了两种截然不同的热带雨林生态系统土壤中含营养物质 DOM 的动态：粘土质陆地森林，以其强大的养分循环和假定的 P 限制而闻名，以及沙质白沙森林，其特征是养分循环能力降低和假定的氮 （N） 限制。利用超高分辨率质谱 （HR-MS），我们分析了溶解的有机营养物质的分子组成。我们应用创新概念证明了养分限制：（1） 通过养碳比评估 DOM 中的养分消耗，（2） 比较不同土壤深度剖面的营养丰富的 DOM 池的组成以推断微生物养分加工，以及 （3） 检查含营养 DOM 的时间变化作为养分吸收和生产的指标。我们的结果证实了陆地森林中 P 限制的假设，还观察到含 N 的 DOM 的显着加工，表明对 P 和 N 的协同需求。令人惊讶的是，白沙土壤没有表现出 N 限制的迹象，而是硫 （S） 限制，这是这些生态系统的一个新发现。 这项研究强调了亚马逊中部潜在营养限制的多样性，以及生物可利用的“黑匣子”DOM 对热带营养循环的重要性。