COS 131-5 - Formations of arbuscular mycorrhizas and ectomycorrhizas increase carbon quality of fine roots and leaves in temperate woody species

Abstract: Two major mycorrhizal types, arbuscular mycorrhizal (AM) and ectomycorrhizal (EM), have been increasingly recognized as key plant functional traits that drive unique ecosystem biogeochemical processes. Specifically, EM-dominated ecosystems are characterized by plant litters with lower litter quality and slower decomposition rates relative to AM-dominated ecosystems. This systematic difference in litter quality and decomposition patterns between EM and AM-dominated ecosystems is central to the mycorrhizal-associated nutrient economy (MANE) framework, which has been shown to efficiently predict ecosystem biogeochemical processes. Whether the differences in plant litter quality are inherent plant traits or induced by different types of mycorrhizas remains unknown.



Here, we tested whether colonization by AM and EM fungi induced differential effects on tissue chemical traits associated with litter quality/decomposition (i.e., lignin content, lignin monomeric composition, the ratio of lignin and nitrogen, and the content of condensed tannins) in fine roots and leaves across two angiosperm and two gymnosperm species, with one species in each clade forming AM and the other forming EM. We also visualized the autofluorescence of lignin in root cross sections using confocal imaging analysis to examine the effects of mycorrhizas on the spatial distribution of lignin deposition.



We showed that EM did not impose a divergent effect on root and leaf recalcitrance compared to AM. Rather, both types tended to decrease the abundance of lignin and condensed tannins. Furthermore, the response in lignin monomeric composition to mycorrhizas was driven by the fundamental difference between gymnosperms and angiosperms irrespective of mycorrhizal type. At the tissue level, mycorrhizal roots showed an enlarged cortex with a smaller, less lignified endodermis compared to non-mycorrhizal counterparts, potentially facilitating symbiosis. These findings indicate that the mycorrhizal-associated alterations in recalcitrance-related chemical traits in both aboveground and belowground tissues are not unique to a mycorrhizal type, thereby questioning the role of mycorrhizal-associated chemical changes as a driver of the previously observed differences in litter decomposition between ecosystems dominated by different mycorrhizal types. Our work suggests that other mechanisms (e.g., mycorrhizal type-specific soil microbial communities) may be more important in explaining MANE framework.