Mycorrhizal symbiosis pathway and edaphic fertility frame root economics space among tree species

The root economics space (RES) is multidimensional and largely shaped by belowground biotic and abiotic influences. However, how root-fungal symbioses and edaphic fertility drive this complexity remains unclear.
Here, we measured absorptive root traits of 112 tree species in temperate and subtropical forests of China, including traits linked to functional differences between arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) hosts.
Our data, from known mycorrhizal tree species, revealed a ‘fungal-symbiosis’ dimension distinguishing AM from ECM species. This divergence likely resulted from the contrasting mycorrhizal evolutionary development of AM versus ECM associations. Increased root tissue cortical space facilitates AM symbiosis, whereas increased root branching favors ECM symbiosis. Irrespective of mycorrhizal type, a ‘root-lifespan’ dimension reflecting aspects of root construction cost and defense was controlled by variation in specific root length and root tissue density, wh...