Hydraulic architecture of crown in three Brazilian species

The hydraulic limitation hypothesis postulates an increase in resistance to water conductivity as trees become taller. Accordingly, we expect that the hydraulic architecture of trees shares a close relationship with the crown architecture and that anatomical traits can directly or indirectly influence hydraulic conductivity. The aim of this work was to investigate the variations in vessels, hydraulic properties and wood density of three native Brazilian tree species. We selected 40-year-old Balfourodendron riedelianum, Cariniana legalis and Handroanthus vellosoi trees and measured maximum vessel length, specific hydraulic conductivity, the percentage loss of conductivity, leaf hydraulic conductivity, and density of branches at three different positions of the crown. Variability in anatomical and hydraulic properties was mostly explained by differences between species, while small differences were related to the position of the branch along the crown-position gradient. Within the measured variables, only the maximum vessel length differed between one crown position and the other. We posit that poor differences between anatomical and hydraulic positions in the crown-position gradient could be related to sample positions within the crown, which were relatively close to each other, with branches having similar ages and diameters. Our findings demonstrate that despite growing in the same environment and having the same age, our species deploy contrasting carbon allocation and hydraulic species-specific strategies. These strategies mirror different growth performances resulting from a different trade-off between hydraulic capacity and safety.