Formations of mycorrhizal symbiosis alter the phenolic heteropolymers in roots and leaves of four temperate woody species

The decomposition rates of senesced tissues from plants associated with ectomycorrhizal (EcM) fungi tend to differ from that associated with arbuscular mycorrhizal (AM) fungi. However, the chemical underpinnings that could drive the observed differences in decomposition are less explored. Here, we characterized the content, composition, and spatial organization of phenolic heteropolymers in roots and leaves of four temperate tree species across eight plant-fungus combinations, forming either AM or EcM associations. Colonization by either AM or EcM fungi tended to decrease the abundance of lignin, condensed tannins, and ratios of lignin and nitrogen in roots and/or leaves, which would lead to lower chemical recalcitrance of tissues. The decrease in root lignin abundance by either mycorrhizal type was associated with an expanded cortex, potentially facilitating symbiosis. Additionally, changes in lignin molecular composition by mycorrhizal symbiosis differed between plant phylogenetic lineages irrespective of mycorrhizal type. Our results suggest that the mycorrhiza-associated changes in plant chemical traits that regulate litter decomposition may not be unique to AM or EcM associations; rather, both associations can reduce root and leaf chemical recalcitrance. Further, the differential modification in lignin composition by mycorrhizal symbiosis between plant phylogenetic groups highlights the influence of plant evolutionary history in plant-mycorrhizal interactions.