Diurnal dynamics in stem dimension is related to water storage use estimated from sap flow measurements at different tree height in the Patagonian conifer Austrocedrus chilensis

SCHOLZ FABIAN G.; BUCCI SANDRA J.; GOLDSTEIN G.

Ghent

Workshop; 9 International Workshop of Sap Flow; 2013

Diurnal water storage use was studied in three large Austrocedrus chilensis trees from South American temperate forests. Changes in water storage were based on simultaneous sap flow measurements by the heat dissipation method at two different heights in the trees, and electronic dendrometers installed in the branches. Diurnal water storage use was calculated from the differences in crown and basal sap flow temporal patterns. Sapwood capacitance was estimated from pressure-volume curves using psychometric methods. The diurnal course of sap flow started first in the branches at 10 m above the ground and then, with a pronounced delay, at the base of the main stem. The beginning of the sap flow at the stem base lagged by 1 h with respect to sap flow in the terminal branches. During the daytime period the sap flow balance between the stem base and terminal branches was negative, that is the integrated water flow of the crown was larger than the water input into the stem near the tree base, suggesting that stored water was withdrawn from the storage by the upper stems during the daytime.  Depleted water storage was recharged in the evening and at night. The withdrawal and recharge of stored water was reflected in large daily dimensional changes in the branch diameter (larger than 0.2 mm). Branch diameter decreased with increasing transpiration and water depletion from storage and increased when transpirational demand ceased and with the refilling of the water storage at nighttime. In addition to the high contribution of stored water to total water use (higher than 20%), this species had high sapwood capacitance, suggesting that the xylem may be an important water storage compartment. Large capacitive release of water and the time shift between basal and crown sap flow reveals that water reservoirs in branches are hydraulically well connected to the water transport system. This species can grow in relatively dry sites, apparently because of an efficient use of the internal water storages during periods of high evaporative demand.