Résumé
1. Water availability is a key determinant of forest ecosystem function
and tree species distributions. While droughts are increasing in frequency
in many ecosystems, including in the tropics, plant responses to water
supply vary with species and drought intensity, and are therefore
difficult to model. Based on physiological first principles, we
hypothesized that trees with a lower turgor loss point (πtlp), i.e., a
more negative leaf water potential at wilting, would maintain water
transport for longer into a dry season. 2. We measured sapflux density of
22 mature trees of 10 species during a dry season in an Amazonian
rainforest, quantified sapflux decline as soil water content decreased,
and tested its relationship to tree πtlp, size, and leaf predawn and
midday water potentials measured after the onset of the dry season. 3. The
measured trees varied strongly in the response of water use to the
seasonal drought, with sapflux at the end of the dry season ranging from
37 to 117% (on average 83 ± 5 %) of that at the beginning of the dry
season. The decline of water transport as soil dried was correlated with
tree πtlp (Spearman ρ≥0.63), but not with tree size or predawn and midday
water potentials. Thus, trees with more drought-tolerant leaves better
maintained water transport during the seasonal drought. 4. Our study
provides an explicit correlation between a trait, measurable at the leaf
level, and whole-plant performance under drying conditions. Physiological
traits such as πtlp can be used to assess and model higher-scale processes
in response to drying conditions.