Monitoring Tree Water Use in the Field
Why tree water use/ transpiration?
- Water is a limiting factor to crop/tree growth
- Transpiration and water uptake have a direct effect on systems productivity and hence food security
- Limited knowledge on water use of different tree species
- Quantify productivity of different components in a system to help advise the right tree for the right place
- Information on this is critical to inform policy (irrigation requirements, limits of species range AEZ)
What is Sap Flow?
- Sap is simply a fluid transported in xylem cells (tracheids or vessel elements)
- Movement of water in plants is based purely on principles of physics
- A gradient in water potential is the physical mechanism that drives water movement in plants
- Water potential is the ability of water to do work
- Plants can have some influence over the passage of water by closing stomata during periods of moisture deficit
- Water moves from a region of high potential to a region of low potential
- Pure water has the largest potential and is given a value of 0 (SI unit for water potential is Pascal (Pa); so water at its reference point has a value of 0Pa)
- The gradient of water potential becomes more negative from the reference point of 0Pa