Impact of freeze–thaw-induced pit aspiration on stem water transport in the subalpine conifer Abies veitchii

During winter, subalpine conifers experience frequent freeze–thaw cycles in stem xylem that may cause embolism and pit aspiration due to increased water volume during the sap to ice transition. This study examined the occurrence and ecological impacts of a combination of freeze–thaw-induced pit aspiration and embolism triggered by natural and artificial stem freezing. In subalpine Veitch’s fir (Abies veitchii) trees, the fraction of closed pits and embolized tracheids as well as conductivity losses were measured to examine pit aspiration and its effects. When trees incurred mild drought stress in February and early March, 70%–80% of stem conductivity was lost. Cryo-scanning electron microscopy indicated