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Water relations in silver birch during springtime: How is sap pressurised?
T Hölttä1,2, M D R Dominguez Carrasco1,2, Y Salmon1,3
1Institute for Atmospheric and Earth System Research, University of Helsinki, Helsinki, Finland.
Plant Biology (Stuttgart, Germany)
|May 8, 2018
Summary
Birch trees in boreal regions generate positive xylem sap pressure to refill winter embolisms. This process involves water transfer from parenchyma cells to xylem vessels, driven by environmental factors.
Area of Science:
- Plant Physiology
- Forest Ecology
- Boreal Science
Background:
- Positive xylem sap pressure occurs in birch trees between soil thaw and bud break.
- This period is crucial for refilling winter-induced xylem embolisms.
- The exact mechanism and environmental drivers of this sap pressurization are not fully understood.
Purpose of the Study:
- To investigate the mechanism and environmental drivers of xylem sap pressurization in boreal birch trees.
- To understand the process of embolism refilling during the pre-bud burst period.
- To analyze the relationship between sap pressure, sap flow, and environmental factors.
Main Methods:
- Measurements of xylem sap flow, pressure, and osmotic concentration.
- Monitoring of xylem and whole stem diameter changes.
- Analysis of stem and root non-structural carbohydrate concentrations.
- Recording of meteorological conditions at two Finnish sites.
Main Results:
- Xylem sap pressure and flow dynamics showed diurnal variations, often inversely related to temperature.
- A net conversion of soluble sugars to starch was observed in stems and roots.
- Xylem sap osmotic pressure was low and did not correlate with environmental changes or tree water status.
Conclusions:
- Xylem sap pressurization and embolism refilling likely occur gradually via water transfer from parenchyma to xylem vessels during the day.
- Parenchyma cells are refilled by soil water uptake primarily during the night.
- The study discusses potential drivers for this water transfer and the performance of thermal dissipation probes under changing stem water content.
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