Water consumption during a leafless period in a dry season in three deciduous tropical timber species

Abstract

Besides mechanical protection and sugar transport through phloem, barks also transpire some amount of water. Bark transpiration may be a driving force to keep water flux during the leafless period among tropical deciduous trees, but has been hardly investigated. In the current investigation we used the sap flow data to assess the water consumption during leaf loss initiation, total leaf loss period, and leaf flush period in three economically important tropical deciduous timber species i.e, Anogeissus acuminata, Dipterocarpus tuberculatus and Tectona grandis. Eight trees of each species were measured using Granier’s heat dissipation sensors, with the circumference ranging from 59 cm to 172 cm (mean 59.84 cm) across the three species. The phenological observation for canopy leaves was also carried out on weekly basis. During the completely leafless period, a significant amount of water flux was detected in all three species, which was correlated with vapor pressure deficit (VPD), and light intensity. The whole tree daily mean water consumption during this leaf-less, flower-less and fruit-less period, mainly due to bark transpiration was around 8–14 kg across the three species. It was about 7 to 18 % of the mean whole-tree daily transpiration in the fully foliated canopies during a typical wet-season period. This water flux was supported by sufficient soil moisture as indicated by the pre-dawn leaf water potential higher than –0.4 MPa in the three species. Further, a significant and positive relationship (R2 = 0.32, P < 0.005) was found between tree circumference and whole-tree water consumption during the leaf-less period. The total stand-level water consumption during the leaf-less period ranged from 13 mm to 26.8 mm on a 30 days basis across the three species. Such water flux mainly driven by bark transpiration could have a significant role in maintaining the hydraulic integrity of trees in the dry season, although it could reduce xylem water potential to a risky level of hydraulic dysfunction during a prolonged drought or on dry sites. The study is the first report on bark transpiration in intact trees, scaled to the stand-level, which should be included in the modeling of hydraulic function of plant and ecosystem hydrology.