Question

What are the limitations of root pressure theory?

Answer 1

Although the ascent of sap takes place due to root pressure, there are certain objections raised, such as:

1. It is not applicable to plants taller than 20 meters.
2. Ascent of sap can also occur even in the absence of a root system.
3. The root pressure value is almost nearly zero in taller gymnosperm trees.
4. In actively transpiring plants, no root pressure is developed.
5. Xylem sap under normal conditions is under tension, i.e., it shows negative hydrostatic pressure or high osmotic pressure.

Thus, root pressure is not the sole mechanism explaining the ascent of sap in all plants of varying heights.