How mycorrhizal fungi could extend plant cognitive processes

Traditionally, mycorrhizas are studied for their role in plant health and nutrition through a mutually beneficial exchange of solutes. Recent research has revealed additional roles for mycorrhizas, including shaping plant communities and enhancing stress resistance. However, a critical aspect for the survival of organisms remains largely ignored in the study of mycorrhizal symbioses: cognition. This review explores the possibility that plants benefit from the cognition and behaviour of mycorrhizal fungi to enhance their own survival. We examine four case studies that are suggestive of plants extending their cognition through mycorrhizal associations: i) foraging complementarity between roots and mycorrhizal fungi; ii) recruitment and abandonment of mycorrhizal fungi depending on the host plant nutritional status; iii) expanded perception of the belowground environment; and iv) shaping the mycorrhizal community to meet survival needs. Whilst extended plant cognition is implied, direct experimental evidence corroborating this hypothesis is needed, and we propose a delimiting criterion with suggestions of experiments to test this hypothesis.