MicroCT imaging of fibre water uptake in sugar maple (Acer saccharum) in response to freezing.

Abstract

We utilised synchrotron based MicroCT to non-invasively observe changes within the xylem of living sugar maple (Acer saccharum Marsh) saplings during a freeze-thaw cycle. Sugar maples naturally develop elevated stem pressures when frozen and then thawed due to a hypothesised mechanism where water is drawn into gas filled fibres during freezing and slowly forced out upon thawing. We extracted information on changes in fibre gas content across the xylem using thresholding. We found a drop in fibre gas content between the initial and frozen states, and then a subsequent recovery in gas content after thaw. These results are consistent with fibres drawing water in during freezing and forcing it out after thawing. Thus, our results provide support for the pressure development mechanism.