问题描述:
英语翻译
Mechanisms for Refilling
Plants may generate the positive pressures necessary for refilling within the roots,throughout the stem,or locally,within the cavitated conduit.The mechanisms by which these processes occur range from fairly well understood in the case of root pressure to poorly understood for the phenomenon of local pressurization.
A.Root pressure:Many species are able to raise the hydrostatic pressure throughout their vascular system by actively loading solutes into their root stele.Osmotically produced “root” pressures,which may reach several hundred kPa,either force emboli into solution or push the air out of hydathodes or open vessel ends (Sperry et al.1987,Fisher et al.1997).Most evidence suggests that this process can only occur when the soil is saturated and transpiration is low,but the critical thresholds at which root pressure is inhibited have not been established experimentally.While the phenomenon is well documented in herbs and vines (Tyree et al.1986,Sperry et al.1987,Fisher et al.1997,Stiller et al.2003),it has only been reported in a small number of trees (e.g.,Sperry et al.1994,Ewers et al.2001).Diurnal refilling via root pressure has been reported in some crop species (Tyree et al.1986,Stiller et al.2003),but it is unclear whether trees employ root pressure for daily recovery of hydraulic conductivity.
Mechanisms for Refilling
Plants may generate the positive pressures necessary for refilling within the roots,throughout the stem,or locally,within the cavitated conduit.The mechanisms by which these processes occur range from fairly well understood in the case of root pressure to poorly understood for the phenomenon of local pressurization.
A.Root pressure:Many species are able to raise the hydrostatic pressure throughout their vascular system by actively loading solutes into their root stele.Osmotically produced “root” pressures,which may reach several hundred kPa,either force emboli into solution or push the air out of hydathodes or open vessel ends (Sperry et al.1987,Fisher et al.1997).Most evidence suggests that this process can only occur when the soil is saturated and transpiration is low,but the critical thresholds at which root pressure is inhibited have not been established experimentally.While the phenomenon is well documented in herbs and vines (Tyree et al.1986,Sperry et al.1987,Fisher et al.1997,Stiller et al.2003),it has only been reported in a small number of trees (e.g.,Sperry et al.1994,Ewers et al.2001).Diurnal refilling via root pressure has been reported in some crop species (Tyree et al.1986,Stiller et al.2003),but it is unclear whether trees employ root pressure for daily recovery of hydraulic conductivity.
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