Sapwood density underlies xylem hydraulics and stored carbohydrates across 13 deciduous tree species in a seasonally dry tropical forest in Thailand

Key message Sapwood density is coordinated with hydraulic capacity and non-structural carbohydrate reserves in xylem in the seasonally dry tropical forests. Abstract Sapwood density (WD) is one characteristic underlying the divergence in life history strategies among species in seasonally dry tropical forests (SDTFs) since WD is liked to xylem hydraulic properties through its correlations with vessel anatomy, maximum photosynthetic capacity, and leaf phenology. However, it remains unclear how differences in WD contribute to the divergence in water conduction and non-structural carbohydrate (NSC) reserves during the dry season, the physiologically most severe period for woody plants. We hypothesized that heavy-wooded species maintain water conduction, photosynthesis, and translocation of carbon which result in high NSC reserves in xylem during the dry season. Using 13 deciduous tree species from a SDTF located in Northeast Thailand, we investigated the variation in WD and bark morphology in relation to hydraulic properties and NSC concentrations in xylem during the late-dry season. Percentage loss of conductivity (PLC) varied as a quadric function of WD: high PLC was observed in light- and heavy-wooded species. The maximum conductivity was not related to WD. The PLC was negatively related to the concentrations of soluble sugars and NSC in the trunk xylem, and these relationships underlined the negative association between WD and NSCs. We also found that species with thick bark showed relatively low PLC, and that dense-barked species exhibited higher NSC concentrations in branch xylem, but their linkages were generally weaker than WD. These results demonstrate that species hydraulics and NSC reserves are coordinated in SDTFs during the dry season, and that WD underlies these divergences.