Data from: Plant functional groups and root traits are linked to exudation rates of mature temperate trees

Root exudation affects soil biogeochemistry profoundly, yet it is rarely
quantified in mature, field-grown trees, and its controls are poorly
understood. We measured rates of carbon (C) exudation in 11 tree species
that exhibit divergent root traits, including gymnosperms and angiosperms
that associate with either arbuscular mycorrhizal (AM) or ectomycorrhizal
(EcM) fungi. Our goal was to explore how tree species, plant functional
groups, and root traits collectively influence exudation patterns.
Species-level differences were modest owing to substantial intraspecific
variability (among individuals of the same species). However, three of the
four highest exuding species were EcM gymnosperms, which exuded ca. two
times more C than the other functional groups. Principal component
analysis revealed that relationships between root trait organization and
exudation were pronounced in EcM-associated trees but weak or absent in
AM-associated trees. In EcM trees, exudation rates were negatively
correlated with root tissue density (RTD) and positively with specific
root area (SRA) and root diameter, driven largely by gymnosperms. In
contrast, exudation in AM trees showed only a weak association with
specific root length. Consistent with these findings, mixed-effect models
also showed that exudation rates were best explained by a combination of
tree-mycorrhizal type, phylogenetic group and SRA, though a large portion
of unexplained variation suggests an important role for contemporary
environmental and local edaphic conditions. Collectively, our results
demonstrate that root exudation is a complex physiological process shaped
by interactions among mycorrhizal association, evolutionary history, and
root traits, rather than by functional groups or root traits alone. These
findings highlight the urgent need for more integrative frameworks and new
experimental approaches to incorporate exudation dynamics into plant
strategy theory and large-scale ecosystem models.