Liquid water content of wood tissue at temperatures below 0°C

Abstract

Time domain reflectometry (TDR) offers an opportunity to measure the liquid water content of otherwise frozen plant material. We applied TDR technology to the examination of freezing in three types of wood represented by Robinia pseudoacacia L. (ring porous), Populus trichocarpa Torr. & A. Gray (diffuse porous), and Pinus contorta Dougl. ex Loud. and Larix occidentalis Nutt. (conifer wood). Gravimetric analysis revealed similar water contents of all wood types during the summer. In contrast, winter data showed that R. pseudoacacia wood exhibited a lower total (liquid and ice) water content (0.250 m3·m-3) than that of Populus trichocarpa (0.600 m3·m-3) or of the two conifer species' wood (0.510 m3·m-3). Additionally,R. pseudoacacia wood contained more air by volume during the winter than all other wood types (air-filled porosity 0.34 m3·m-3 compared with 0.12-0.22 for all other species). At all temperatures below 0°C, R. pseudoacacia wood contained less liquid water than the other wood types, as revealed by TDR measures. The TDR analysis further demonstrated that more than 25% of the water in wood of all species was liquid even at temperatures of -15°C. This liquid water is likely found within the cell wall and is potentially transportable at temperatures well below 0°C.