Contrasting mycorrhizal growth responses in native and invasive woody species are associated with distinct root trait syndromes

Invasive plant species often express resource-acquisitive leaf traits that
support rapid growth, but associated fine root traits and the role of
microbial mutualists in invader whole-plant functioning remains poorly
understood. We performed an experiment of 12 phylogenetically-grouped
native and non-native, invasive woody species, grown with or without a
common inoculum of arbuscular mycorrhizal fungi (AMF) across two nutrient
levels. We measured 10 fine root traits associated with nutrient uptake
and suitability of AMF colonization. The presence of AMF increased the
growth rate of all species, but native species were significantly more
dependent on AMF than invaders. Further, invaders expressed a distinct
syndrome of first-order root traits, including longer, thinner roots of
high specific root length, greater branching intensity, and lower tissue
density, which are traits associated with rapid nutrient uptake and low
AMF association. This syndrome was independent of phylogeny, AMF
inoculation, and soil fertility. An acquisitive fine root trait syndrome
for invaders supports high photosynthetic and growth rates, linking above-
and below-ground functioning. The occurrence of this syndrome across
phylogenetic groups indicates that lineages of woody invaders typically
associated with arbuscular mycorrhizas may be generally less dependent on
AMF than native species.