Abstract:
Root anatomical traits regulate water transport and resource acquisition in forest ecosystems,
yet their variation and coordination with aboveground traits remain poorly understood
in tropical forests. We investigated patterns of interspecific variation in four root
anatomical traits (vessel diameter, vessel density, vessel lumen fraction, and theoretical
hydraulic conductivity) across 20 tree species representing contrasting growth strategies
in a premontane tropical forest of southern Ecuador. Using 160 root samples from transport
roots (4–8 mm diameter), we quantified anatomical traits through microscopy and
calculated theoretical hydraulic conductivity. We analyzed correlations with wood density
and leaf functional traits and performed principal component analyses to assess trait coordination.
Species exhibited substantial variation in root anatomical traits, ranging from
acquisitive strategies with large vessel diameters (67.6 μm in Ocotea sp.) and high hydraulic
conductivity (73.9 kg m−1 MPa−1 s−1 in Alchornea glandulosa) to conservative strategies
with high vessel density (>185 vessels/mm2 in Leonia crassa and Aspidosperma rigidum).
However, 60% of species displayed intermediate trait values, suggesting compensatory
strategies rather than extreme specialization. We documented strong negative correlations
between vessel diameter and both vessel density (r = −0.74) and wood density (r = −0.51),
pointing at hydraulic efficiency-safety trade-offs. Principal component analysis revealed
that leaf traits operated orthogonally to root anatomical traits, indicating independent
axes of functional variation rather than coordinated whole-plant strategies. These decoupling
challenges traditional plant economics spectrum assumptions and evidence that
plants optimize above- and belowground functions through independent evolutionary
pathways. Our findings highlight the prevalence of intermediate hydraulic strategies in
tropical tree communities and provide new insights into the functional organization of
diverse forest ecosystems.
