Root push, also known as root pressure, is a phenomenon that helps drive water upward in plants, particularly when transpiration is low.
Understanding Root Push
The process of root push is initiated by the active accumulation of ions within the root's vascular tissue.
The Steps Involved in Root Push
Based on the provided information, the mechanism unfolds as follows:
- Ion Accumulation: Ions are actively transported or accumulate within the root xylem.
- Osmotic Potential Change: As ions accumulate in the root xylem, the osmotic potential of the xylem solution falls. This means the solution becomes more concentrated.
- Water Uptake (Osmosis): The lower osmotic potential inside the xylem causes the passive uptake of water from the soil by osmosis into the xylem. Water moves from an area of higher water potential (soil) to an area of lower water potential (xylem).
- Pressure Buildup: As water enters the rigid xylem vessels, pressure builds up within the xylem due to osmotic water uptake.
- Upward Movement (Mass Flow): As pressure builds up within the xylem due to osmotic water uptake, the xylem solution is forced upward to the leaves by mass flow. This positive pressure pushes the water column upwards.
This pressure is typically observed most readily when transpiration rates are low, such as during the night or in humid conditions. While root pressure contributes to water transport, especially over short distances or in young plants, it is generally not strong enough to lift water to the tops of very tall trees; that role is primarily fulfilled by transpiration pull.
Root pressure can sometimes lead to guttation, where water is forced out of specialized pores (hydathodes) on the edges of leaves, often visible as droplets in the morning.
