PLHL 3060 Lecture : Lecture 5
Document Summary
Why: root pressure is a positive hydrostatic pressure in the xylem of roots. The water potential of the root and the soil are about the same. In the root xylem cells (which don"t have membranes) solutes accumulate. It"s not a lot of solutes, but it is enough to reduce the osmotic potential of the solution in the xylem. This creates a water potential gradient for water to move into the xylem. Again, this is small amounts of solute but is enough to create positive pressure in the root xylem. As a result, water is pushed up the xylem. Root pressure conditions: closed stomates, well watered or high soil water potential, mostly occurring at night, guttation is an exudation of liquid from the leaves due to root pressure. Hydathodes are specialized pores for water release during guttation: positive root pressure is beneficial to the plant because at night it allows a significant amount of recovery to the plant at night.
