Managing ion concentration in sap to control drying collapse, permeability, and streaming potential in plantation-grown eucalyptus timber

Wood is an important renewable resource for a future sustainable bioeconomy. Ion-mediated response in wood is considered a major factor in sap-flow regulation. This study examined the influence of sap replacement with KCl solution and deionised water on drying collapse, wood permeability, and streaming potential of never-dried wood. Volumetric and tangential collapse in KCl-treated Eucalyptus nitens logs decreased significantly by 42%- 62% and by 51%, respectively. Improvement in shrinkage properties was concentration-dependent, with a maximum at a concentration (20 mM) in the range of total ionic strength found in living trees. Logs treated with deionised water showed higher normal shrinkage, without affecting collapse. Consistent with reduced collapse in KCl-treated logs, eucalyptus stem cores showing low collapse contained significantly more inorganic cations than the high-collapsed wood. The decrease in collapse when treated with KCl solution coincided with increased green wood permeability. Sap conductivity affected the streaming potential, with the polarity of the induced electric potential varying between concentrations and matching literature reports of electric potential measurements in living trees and laboratory experiments. This study confirmed that drying collapse was negatively correlated to sap conductivity, and potential technological solutions to drying collapse in E. nitens could include sap replacement as a pre-drying treatment, and/or nutrient management of the plantations.