Time lags between crown and basal sap flows in tropical broadleaf and temperate conifer trees
Sap flow transportation from root to leaf in trees is explained by the cohesion of water molecules pulled up by tension due to transpiration. However, in some species, it has been observed that there can be several minutes to hours of time-lag in sap flow between the crown and the base of the stem. This time lag is assumed to be a proxy for the capacity of water storage to supply water for transpiration. To examine whole-tree water use in relation to internal stem water storage, we measured crown and basal sap flow using hand-made Granier sensors in tropical broadleaf and temperate conifer trees. Measurements on tropical broadleaf trees were conducted at the Pasoh Forest Reserve in Peninsular Malaysia with Dipterocarpus sublamellatus (height = 45 m, DBH = 69 cm) a dominant emergent tree species, and Ptychopyxis caput-medusae (height = 32 m, DBH = 38 cm), a canopy tree adjacent to D. sublamellatus. Measurements on temperate conifers were conducted at the Kiryu Experimental Forest in central Japan with Chamaecyparis obtusa (height = 20 m, DBH = 20-60 cm), an important plantation tree in Japan. In D. sublamellatus, very narrow time lags between crown and basal sap flows were observed, suggesting internal stem water storage contributed little to daytime whole-tree water use. In P. caput-medusae and C. obtusa, basal sap flow started later than crown sap flow in the morning, suggesting partial reliance on internal stem water storage for daytime whole-tree water use. Additionally, basal sap flow continued until midnight, after the crown sap flow had stopped, indicating refilling of internal stem water storage during the night.
Azuma, W.A., Kosugi, Y., Tsuruta, K. and Lion, M. (2020). Time lags between crown and basal sap flows in tropical broadleaf and temperate conifer trees. Acta Hortic. 1300, 105-112
water relations, water storage, tall tree, rehydration, Dipterocarpaceae, Euphorbiaceae, Cupressaceae