Mycorrhizal fungi respond to resource inequality by moving phosphorus from rich to poor patches across networks

The world’s ecosystems are characterized by an unequal distribution of resources. Trade partnerships between organisms of different species - mutualisms - can help individuals cope with such resource inequality. Trade allows individuals to exchange commodities they can provide at low cost, for resources that are otherwise impossible, or more difficult, to access. However, as resources become increasingly patchy in time or space, it is unknown how organisms alter their trading strategies. Here we show how a symbiotic fungus mediates trade with a host root in response to different levels of resource inequality across its network. We developed a quantum-dot tracking technique to quantify phosphorus trading strategies of arbuscular mycorrhizal fungi simultaneously exposed to rich and poor resource patches. By following fluorescent nanoparticles of different colors across fungal networks, we determined where phosphorus was hoarded, relocated and transferred to plant hosts. We found that incr...