Arbuscular mycorrhizal fungi function as conduits for underground nutrient transport. While the fungal partner is dependent on the plant host for its carbon (C) needs, the amount of nutrients that the fungus allocates to hosts can vary with context. Because fungal allocation patterns to hosts can change over time, they have historically been difficult to quantify accurately. We developed a technique to tag rock phosphorus (P) apatite with fluorescent quantum-dot (QD) nanoparticles of three different colors, allowing us to study nutrient transfer in an in vitro fungal network formed between two host roots of different ages and different P demands over a 3-week period. Using confocal microscopy and raster image correlation spectroscopy, we could distinguish between P transfer from the hyphae to the roots and P retention in the hyphae. By tracking QD-apatite from its point of origin, we found that the P demands of the younger root influenced both: (1) how the fungus distributed nutrients among different root hosts and (2) the storage patterns in the fungus itself. Our work highlights that fungal trade strategies are highly dynamic over time to local conditions, and stresses the need for precise measurements of symbiotic nutrient transfer across both space and time.

丛枝菌根真菌起地下营养物运输的管道的作用。尽管真菌伴侣的碳（C）需求依赖于植物宿主，但真菌分配给宿主的营养素含量会随环境而变化。由于对宿主的真菌分配模式会随着时间而变化，因此从历史上讲，很难对其进行准确量化。我们开发了一种使用三种不同颜色的荧光量子点（QD）纳米粒子标记磷磷灰石的技术，从而使我们能够研究在不同年龄和不同磷需求的两个寄主根之间形成的体外真菌网络中的养分转移在3周的时间内。使用共聚焦显微镜和光栅图像相关光谱法，我们可以区分从菌丝到根的磷转移和菌丝中的磷保留。通过从QD-磷灰石的起源处追踪，我们发现年轻根的磷需求影响了以下两个方面：（1）真菌如何在不同根宿主之间分配养分，以及（2）真菌本身的存储模式。我们的工作突出表明，真菌贸易策略随时间的推移会随当地情况的变化而动态变化，并强调需要精确测量跨时空共生营养素转移的情况。