Xylem dielectric constant, water status, and transpiration of young Jack Pine (Pinus banksiana Lamb.) in the southern boreal zone of Canada

Diurnal changes of xylem dielectric constant (XDC), microclimate, and tree water status were studied in a young Jack Pine (Pinus banksiana Lamb.) stand in the southern boreal zone of Canada. Tree water status of trees was also manipulated by changing the canopy vapor pressure gradients in order to evaluate its influence on tree hydraulic conductance. Seasonal stand water consumption was calculated from tree transpiration. The mean XDC of eight concurrently monitored trees changed significantly from day- to nighttime. Individual trees varied widely in trend and diurnal amplitude of XDC changes. Correlation between individual tree´s XDC, micro-meteorological parameters, tree water status and xylem flux was weak. Changes of XDC were observed during short term manipulation of water potential while tree water content did not change significantly. Xylem flux in trees was linearly related to the xylem water potential gradient. Tree hydraulic conductance was weakly correlated with xylem water potential and atmospheric vapor pressure deficit. No significant relationship was found between tree water potential and water content. Stand transpiration was depending on available soil water, reflected in a strong decreasing trend of transpiration vs. atmospheric vapor pressure differences during periods of water storage depletion