Is leaf spectral reflectance an integrator of mycorrhizal types?

Light reflectance by foliage across visible and infrared wavebands is determined by chemical and structural traits that reveal how plants evolved to support growth and defense in different climate and environments. These spectral fingerprints have emerged as powerful tools to estimate plant functional and taxonomic diversity across scales, giving rise to a new approach in ecology called spectranomics. In this context, the widespread co-evolution of plants with different mycorrhizal fungi has likely led to chemical, structural and thus spectral dissimilarities that are strong enough to be intrinsic features of each mycorrhizal association. Such spectral dissimilarities may therefore help to better estimate the mycorrhizal dominance and associated belowground functions at large scales using remote sensing techniques. From a combination of chemical and spectral measurements on leaves of 32 European tree species forming either arbuscular (AM) or ectomycorrhizal (EM) symbiosis, we investigated the existence of “mycorrhizal optical types” and the leaf traits that may underpin them. Our results demonstrate that tree species associated with AM and EM fungi have distinct leaf colour and spectral fingerprints that can be linked to differences in leaf metabolism. In this talk, I will discuss the various factors that may have led to these spectral fingerprints as well as the potential and constraints of aboveground spectral signals acquired at the large scale to serve as optical surrogates of plant mycorrhizal associations and belowground function.