Discussion
Here, we presented the first formal hypothesis test of links among the
evolution of root traits, leaf traits, and mycorrhizal state in seed
plants and its main clades. Our results indicate that the substantial
evolutionary shifts in root diameter and SRL of seed plants were
correlated with leaf traits that facilitate enhanced hydraulic capacity
and greater photosynthetic performance in the canopy, but also with
changes in growth form. The reconstruction of trait values across the
phylogeny suggest that switches to ECM associations could have impacted
the morphology of Gymnosperm root systems, but had limited influence on
Angiosperms. Indeed, Rosids and Asterids apparently evolved thinner,
longer root systems before the evolution of ECM or Ericoid associations.
Similarly, the evolution of the NM state associated with additional
decreases in diameter and RTD, plus increases in SRL in Angiosperms, but
those changes were also correlated with transitions from woody to
herbaceous habit.