Preferential allocation, physio‐evolutionary feedbacks, and the stability and environmental patterns of mutualism between plants and their root symbionts

• Published in: The New phytologist Vol. 205; no. 4; pp. 1503 - 1514
• Main Author: Bever, James D
• Format: Journal Article
• Language: English
• Published: England Academic Press 01-03-2015; New Phytologist Trust; Wiley Subscription Services, Inc
• Subjects: Arbuscular mycorrhizas; Biological Evolution; carbon; carbon allocation; Carbon dioxide; cheater; Coexistence; Dynamic stability; Environment; evolution; Feedback, Physiological; Fungi; hosts; Model testing; Models, Biological; Mutualism; mycorrhizal fungi; mycorrhizas; Phosphorus; Physiology; physio‐evolutionary feedbacks; Plant Roots - microbiology; Plants - microbiology; Plastic properties; Plasticity; Population Dynamics; preferential allocation; soil; Stability analysis; Symbionts; Symbiosis; Symbiosis - physiology; theory; Uptake; symbiosis; mycorrhizas; carbon allocation; physio-evolutionary feedbacks; cheater; preferential allocation; theory; mutualism
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.13239

The common occurrence of mutualistic interactions between plants and root symbionts is problematic. As the delivery of benefit to hosts involves costs to symbionts, symbionts that provide reduced benefit to their host are expected to increase in frequency. Plants have been shown to allocate preferentially to the most efficient symbiont and this preferential allocation may stabilize the mutualism. I construct a general model of the interactive feedbacks of host preferential allocation and the dynamics of root symbiont populations to evaluate the stability of nutritional mutualisms. Preferential allocation can promote the evolution of mutualism even when the cost to the symbiont is very large. Moreover, the physiological plasticity of preferential allocation likely leads to coexistence of beneficial and nonbeneficial symbionts. For arbuscular mycorrhizal fungi, which facilitate plant uptake of phosphorus (P), the model predicts greater P transfer from these fungi per unit carbon invested with decreasing concentrations of soil P and with increasing concentrations of atmospheric CO₂, patterns that have been observed in laboratory and field studies. This framework connects physiological plasticity in plant allocation to population processes that determine mutualism stability and, as such, represents a significant step in understanding the stability and environmental patterns in mutualism.