root pressure


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Fig. 272 Root pressure . The mercury enables root pressure to be measured.

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.
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droplets can be observed when "root pressure" reaches a
process of guttation takes place due to root pressure (Singh &
or physical force theory or root pressure theory or the combination of
The process of root pressure forcing water out of the leaves is termed guttation and only occurs when stomata are closed and when water is readily available to the root system, usually overnight Although capable of forcing water up the xylem when all the stomata are closed, when they are open, root pressure is a negligible component of water movement.
On the basis of correlation analysis, cultivars that interacted positively with Di and Dv had earlier maturity, higher root pressure under stress, higher soil water content at the end of the vegetative stress period, high leaf chlorophyll content at midgrainfilling, large reduction in radiation interception with vegetative stress, low %FW in WS and Fc, and high epidermal conductance.
Other traits that differed among cultivar groups, but were not consistently related to maturity, included root pressure in Di, %FW, leaf chlorophyll measured during grainfilling stress, and epidermal conductance.
The first principal component axis cultivar score was positively correlated with maturity, %FW in WS and in Fc, and negatively correlated with root pressure in Dv and soil moisture remaining in the soil after 3 wk of water exclusion in Dv (Table 4).
cordifolia can restore water transport during spring in vessels embolized during winter (Sperry, 1993), and because birches generally show root pressure in spring (Johnson, 1944), maximum stem conductivity (assumed to reflect the natural state of twigs in early summer) of the two species was used to test whether hydraulic limitations might be differentially affecting leaf P in B.
Plant physiologists have shown that high root pressure can provide one explanation for the arboreal habit of palms (Davis, 1961) and other monocots (Fisher et al., 1997a, b), and that the valve-like nature of the juncture between stems and adventitious roots in Agave explains how Agave can occupy desert habitats (Ewers et al., 1992).
Root pressure is pronounced in some monocots (Davis, 1961) and is a widespread phenomenon in monocots as well as certain non-monocots (Ewers et al., 1997; Fisher et al.
It is hypothesized that root pressure in vines helps reduce the risk of water stress-induced embolism.
Other studies found that vines exhibited positive root pressures at night or after rainstorms, a phenomenon uncommon in trees and shrubs (Ewers et al., 1991) Results have suggested that temperate Vitis species use root pressure as a necessary feature to overcome freeze-induced cavitation during the winter (Fisher et al., 1997).