Plants can manipulate the solute potential and pressure potential within tissues in order to establish water potentials that facilitate movement

• Transpiration involves the generation of negative hydrostatic pressures within the leaves (via evaporation) and positive hydrostatic pressures within the roots

• This pressure differential creates tension within the xylem vessels that allow water to be transported against gravity via capillary action

Root Pressure

Root pressure is a positive pressure potential within the root tissue that can generate water movement up the xylem

• Root pressure can allow water to move up the stem when transpiration is insufficient (e.g. when humidity is high or before bud burst in spring)
  

Plants control the uptake of water from the soil by regulating the movement of mineral ions via indirect active transport

• Root cells contain proton pumps that actively expel H+ ions (stored in the vacuole of root cells) into the surrounding soil
  

• The H​+ ions displace the positively charged mineral ions from the clay, allowing them to diffuse into the root along a gradient
  

• Water will follow the mineral ions into the root via osmosis – with the rate of water uptake regulated by water channels (aquaporins) on the root cell membrane
  

Mineral Uptake in Roots