Final Report Summary - MARKETS (The evolution of plant-fungal markets)
Biological market theory provides a conceptual framework to analyze trade strategies in symbiotic partnerships. An open question is how trade is affected by abrupt and extreme changes in resource availability. Partner discrimination has been well studied, however, it is still unknow if or how partners can control (or influence) the value of the traded resource. While this question has been difficult to test in animal systems, the arbuscular mycorrhizal symbiosis - characterized by complex networks of roots and fungi trading resources - allows for precise spatial and temporal manipulation of trade. We quantified fungal trading strategies across a wide range of conditions, using a recently developed technique in which we tag nutrients with fluorescing quantum-dots of different colors and track their movements. We found evidence that fungal trade strategies are not uniform across the symbiotic network. We showed how active, dynamic resource movement is used by fungi to mediate resource value. We identified a series of trade strategies enacted by the fungus, including: (i) differentially moving resources within the network from rich to poor patches to capitalize on host nutrient demand, (ii) compensating for resource loss by transferring P from alternative pools closer to the host root, and (iii) retaining surplus nutrients until plant demand – and thus nutrient value - increase. Our data hint at an amazing level of sophistication in fungal trading strategies. Our results suggest that even microenvironments of resource heterogeneity can alter the way symbiotic organisms exchange resources. More broadly, our work opens up a new line of research into the properties that shape complex trade decisions in the absence of cognition.