Stored water in the inner bark and sapwood: Atypical patterns of daily discharge and recharge, radial osmotic gradient and freezing resistance

Stored water in inner tissues can affect plant water balance and its freezing resistance. We studied the water storages in the inner bark and sapwood of Araucaria araucana, a species with thick inner bark. Specifically, we analyzed its daily behavior, the driving force to radial water movement and its freezing resistance. The whole-stem water content and diameter and sap flow increased in the morning and decreased in the afternoon. An osmotic gradient between stem tissues was involved in the morning water storage recharge. There were no lags in the onset of sap flow between different stem positions, however sap flow at 6m height was higher than basal sap flow in the afternoon, at the time that sapwood water content started to decline followed by the inner bark. Extracellular freezing was delayed down to -6˚C in the inner bark and to -8˚C in the leaves. The unusual diurnal pattern of internal water use may enhance freezing resistance as a consequence of the lower water content and higher osmotic potential when the lowest temperatures occur. The contribution of stem tissues to daily water use and the pattern of ice nucleation observed make this species less susceptible to drought and very low temperatures.