Sublethal Cd exposure stimulates Laccaria bicolor x poplar symbiosis formation

Abstract Soils have become increasingly polluted with Cd due to industrial and mining activities, as well as agricultural fertiliser usage. Because of its toxicity, plants face significant abiotic stress. Trees found in temperate and boreal forest ecosystems rely on their mutualistic relationship with ECM fungi to alleviate the toxic effects of Cd. In this study, we assessed the impact of Cd pollution on both L. bicolor and its symbiosis with P. tremula x alba . We investigated the impact of Cd pollution on fungal growth and mycorrhiza morphology, as well as the expression of symbiosis marker genes and ROS scavenging enzymes in presence and absence of a host plant. Results indicate that fungal growth is reduced by exposure to elevated Cd, however symbiosis formation is stimulated. Both symbiosis marker genes and ROS scavenging enzymes showed increased expression upon exposure to Cd, but only in the presence of a host plant. This data suggests that forming the ECM symbiosis is a key coping mechanism for both poplars and L. bicolor , and by stimulating the formation of the symbiotic structure, the reduced fungal growth can partially be mitigated. This research highlights the importance of the ECM symbiosis in both plant and fungal resilience in changing environmental conditions.