Q.What are the limitations of root pressure theory?
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Start your 14-day free trial to unlock the full solution →Limitations of the root pressure theory: root pressure is not observed in many plants (especially tall trees, gymnosperms and plants under high transpiration); it is generally too weak (usually a few atmospheres) to p...
Root pressure is too weak, absent in many plants, and metabolically dependent, so it cannot fully explain the ascent of sap.
Root pressure — the positive hydrostatic pressure developed in the xylem due to active absorption of water and ions by root cells — was one of the earliest theories proposed to explain the ascent of sap, but it has several important limitations: (1) It is not universally observed; many plants, especially gymnosperms and most tall trees, show little or no measurable root pressure. (2) Even where present, root pressure is generally quite small (typically not more than 1-2 atmospheres), which is far too weak to push water to the top of very tall trees (which may need pressures of 20 atmospheres or more). (3) Root pressure depends on active metabolic processes in root cells (respiration, ion uptake), so it is markedly reduced or abolished under conditions of low temperature, poor soil aeration, or metabolic inhibitors. (4) Root pressure phenomena like guttation (exudation of water droplets from leaf margins) are usually seen at night or early morning when transpiration is low or absent; during the day, when transpiration rates are high, the rate of water ascent far exceeds what root pressure alone could produce. For these reasons, root pressure is now regarded as a relatively minor, secondary mechanis …
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