Root Pressure


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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.

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It was positively related to maturity, stemborer score, flowering delay, and leaf area, but was negatively correlated with root pressure, soil moisture at the end of the stress period, leaf chlorophyll during grainfilling stress, CT in Fc, and %FW in Fc (Table 4).
Root pressure may also play an important role in refilling cavitated xylem vessels.
Cultivars that tended to interact positively with stress environments had root traits associated with stress avoidance (long roots, high root pressure with stress) and leaf traits that were not stress-avoiding (little rolling and high CT).
Root pressure (which is controlled by parenchyma in ways not fully demonstrated yet) may also play a rote in countering vulnerability in wide vessels such as those of palms (Davis, 1961).
Davis (1961) showed that root pressure in palms could exceed 10 m, thus accounting for conductive characteristics of palms--perhaps most notably, how embolisms could be reduced and cleared should they form.
They, like grasses, may have conductive systems that operate to an appreciable extent on root pressure, and thereby are able to occupy habitats different from those of the monocots without vessels in stems and leaves.
Palms are capable of unusually high root pressures, which may be achieved by with the aid of parenchyma sheaths that can mediate ion and photosynthate content of vessels.