root pressure
root pressure
root′ pres`sure
n.
n.
Root Pressure
Root Pressure
pressure arising in the conducting vessels of plant roots. Along with transpiration, root pressure causes sap (water and dissolved nutrients) to rise up through the stem. Root pressure is caused by osmosis: the cells of the root secrete mineral and organic matter into the vessels, creating greater osmotic pressure than in the soil solution. Root pressure is usually equal to 1–3 atmospheres (in some cases reaching 10 atm; 1 atm = 105 newtons per sq m). Root pressure depends on the conditions of vital activities of the root. At low temperatures or when oxygen is lacking, the root pressure declines, and at the death of the root it is zero. The maximum root pressure occurs during the day, the minimum at night.
root pressure
root pressure
a force exerted within a plant root that pushes water up towards the stem. The phenomenon is produced by the root cells having a solute concentration gradient which increases from outside the root towards the centre of the root. Thus, by OSMOSIS, water passes from the soil, across the root and into the xylem as a result of salt excretion by the ENDODERMIS into the xylem, creating pressure which can be observed in a plant with the aerial parts removed.- knock-on effect
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