Juuripainesysteemit

Juuripainesysteemit, known in English as root pressure systems, are a physiological phenomenon in plants where water is actively transported from the xylem into the xylem vessels in the root, creating a positive pressure. This pressure can push water upwards in the plant's vascular system, particularly noticeable when transpiration rates are low.

The process begins with the active uptake of mineral ions by root cells, which then accumulate in the xylem. Water follows these ions via osmosis, moving from the soil into the root xylem. This influx of water, coupled with the inward movement of ions, generates the positive pressure.

Root pressure is a significant factor in water transport in smaller plants or during humid conditions when transpiration is limited. It can be observed as guttation, where water droplets are exuded from the tips or margins of leaves. This phenomenon is distinct from transpiration, which is the evaporation of water from plant surfaces, primarily through stomata.

While root pressure plays a role in water movement, it is generally insufficient to move water to the top of tall trees. In taller plants, the cohesive and adhesive properties of water, combined with the pull created by transpiration (transpiration pull), are the dominant forces driving water transport. Nevertheless, root pressure can contribute to the initial upward movement of water and help maintain a continuous column of water in the xylem.