Résumé
Plants are enormously diverse in their traits and ecological adaptation,
even within given ecosystems, such as tropical rainforests. Accounting for
this diversity in vegetation models poses serious challenges. Global plant
functional trait databases have highlighted general trait correlations
across species that have considerably advanced this research program.
However, it remains unclear whether trait correlations found globally hold
within communities, and whether they extend to drought tolerance traits.
For 134 individual plants spanning a range of sizes and life forms (tree,
liana, understory species) within an Amazonian forest, we measured leaf
drought tolerance (leaf water potential at turgor loss point, πtlp),
together with 17 leaf traits related to various functions, including leaf
economics traits and nutrient composition (leaf mass per area, LMA; and
concentrations of C, N, P, K, Ca, and Mg per leaf mass and area), leaf
area, water use efficiency (carbon isotope ratio), and time-integrated
stomatal conductance and carbon assimilation rate per leaf mass and area.
We tested trait coordination and the ability to estimate πtlp from the
other traits through model selection. Performance and transferability of
the best predictive model were assessed through cross-validation. πtlp was
positively correlated with leaf area, and with N, P and K concentrations
per leaf mass, but not with LMA or any other studied trait. Five axes were
needed to account for >80% of trait variation, but only three of
them explained more variance than expected at random. The best model
explained only 30% of the variation in πtlp, and out-sample predictive
performance was variable across life forms or canopy strata, suggesting a
limited transferability of the model. Synthesis. We found a weak
correlation among leaf drought tolerance and other leaf traits within a
forest community. We conclude that higher trait dimensionality than
assumed under the leaf economics spectrum may operate among leaves within
plant communities, with important implications for species coexistence and
responses to changing environmental conditions, and also for the
representation of community diversity in vegetation models.