Ecological applications of differences in the hydraulic efficiency of palms and broad leaved trees

Key message In tropical forests, co-occurring woody monocot and dicot species adapted different water use strategies highly depending on their investment in the hydraulic conduit properties. Abstract We studied the hydraulic efficiency of palms and broad-leaved tropical tree species from a moist tropical lowland forest in the Central Brazilian Amazon. Therefore, we harvested 34 trees and 10 ac¸ai palms and measured vessel size and frequency at diameter at breast height and additionally at the base of the crown shaft for the palms. Further, we assessed the active xylem area to estimate the hydraulic conductivity through Hagen Poiseuille’s adapted theoretical equation. Mean vessel diameter in dicot trees was 127.62 ± 49.22 lm with an average 9.09 ± 6.50 vessels per mm2. Mean conduits sizes at the base (h = 0.10 m) of palm trees were larger with 288.20 ± 32.96 lm and less frequent with 1.40 ± 0.46 vessels per mm2. Hydraulic conductivity was on average 3.31 ± 4.59 kg m-1 s-1 MPa-1 for dicot trees. Mean hydraulic conductivity in ac¸ai palms was 20.45 ± 10.6 kg m-1 s-1 MPa-1 at the base, and increased to 124.73 ± 55.2 kg m-1 s-1 MPa-1 at the crown base. Hydraulic conductivity at the base of the crown was higher than in the base of the trunk due to the high density of vessels in a small cross-section in this height. Furthermore, we found a species-independent relationship between vessel diameter and frequency. We conclude that the differences found in the hydraulic efficiency give some evidence that palms have a lower occurrence of embolism and cavitation than trees, which is due to stiffer and stronger conduit pathways and efficient drought-avoiding strategies. The differences in hydraulic architecture between palms and trees imply different water use patterns thus varying niche differentiation, but this does not consequently need to be an excluding factor for coexistence in the same environment