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Hydraulic and osmotic properties of spruce roots

Title data

Rüdinger, Marcus ; Hallgren, Stephen W. ; Steudle, Ernst ; Schulze, Ernst-Detlef:
Hydraulic and osmotic properties of spruce roots.
In: Journal of Experimental Botany. Vol. 45 (October 1994) Issue 279 . - pp. 1413-1425.
ISSN 1460-2431
DOI: https://doi.org/10.1093/jxb/45.10.1413

Abstract in another language

Hydraulic and osmotic properties of roots of 2-year-old Norway spruce seedlings (Picea abies (L.) Karst) were investigated using different techniques (steady flow, pressure probe, and stop flow technique). Root pressures were measured using the root pressure probe. Compared to roots of herbaceous plants or deciduous trees, excised root systems of spruce did not develop appreciable root pressure (-0.001 to 0.004 MPa or -10 to 40 cm of water column). When hydrostatic pressure gradients were used to drive water flows across the roots, hydraulic conductivities (L(pt)) were determined in two types of experiments: (i) root pressure relaxations (using the root pressure probe) and (ii) steady flow experiments (pneumatic pressures applied to the root system or xylem or partial vacuum applied to the xylem). Root L(pr) ranged between 0.2 and 8 x 10(-8) m s(-1) MPa(-1) (on average) depending on the conditions. In steady flow experiments, L(pr) depended on the pressure applied (or on the flow across the roots) and equalled (0.19+/-0.12) to (1.2+/-1.7)x10(-8) m s(-1) MPa(-1) at pressures between 0.2 and 0.4 MPa and (1.5+/-1.3)x10(-8) m s(-1) MPa(-1) at applied pressures between 0.8 and 1.0 MPa. When pressures or vacuum were applied to the xylem, L(pr) values were similar. The hydraulic conductivity measured during pressure relaxations (transient water flows) was similar to that obtained at high pressures (and water flows). Although there was a considerable scatter in the data, there was a tendency of the hydraulic conductivity of the roots to decrease with increasing size of the root system. When osmotic gradients were used to drive water flows, L(pr) values obtained with the root pressure probe were much smaller than those measured in the presence of hydrostatic gradients. On average, a root L(pr)=0.017 x 10(-8) was found for osmotic and L(pr)=6.4 x 10(-8) m s(-1) MPa(-1) in corresponding hydrostatic experiments, i.e. the two values differed by a factor which was as large as 380. The same hydraulic conductivity as that obtained in osmotic experiments using the pressure probe was obtained by the 'stop flow technique'. In this technique, the suction created by an osmoticum applied to the root was balanced by a vacuum applied to the xylem. L(pr) values of root systems did not change significantly when measured for up to 5 d. In osmotic experiments with different solutes (Na2SO4, K2SO4, Ca(NO3)(2), mannitol), no passive uptake of solutes could be detected, i.e. the solute permeability was very low which was different from earlier findings on roots of herbs. Reflection coefficients of spruce roots (sigma(sr)) were low for solutes for which plant cell membranes exhibit values of virtually unity to (sigma(sr) = 0.18-0.28 for Na2SO4, K2SO4, Ca(NO3)(2), and mannitol). On average, reflection coefficients of spruce roots were smaller by about a factor of two than those obtained in the past for roots of herbaceous species. To test for an influence of active nutrient transport and osmoregulatory processes on the absolute value of the root reflection coefficients measured, model calculations were performed. The results showed that huge changes in active pumping rates (changes of several hundred per cent) would be required to account for the same changes in root pressure when assuming a root sigma(sr) = 1 and that responses were completely controlled by active processes, The large differences in hydraulic conductivity between osmotic and hydrostatic water flow and low reflection coefficients (at a low solute permeability) are explained by the composite transport model of the root recently introduced. The model also explains the non-linear relation between water flow and driving forces, i.e. the variable hydraulic resistance of roots which has often been reported in the literature. It is concluded that both the low root sigma(sr) and low rates of active solute uptake cause part of the low root pressures observed in conifers.

Further data

Item Type: Article in a journal
Refereed: Yes
Additional notes: BAYCEER33690
Institutions of the University: Research Institutions > Research Centres > Bayreuth Center of Ecology and Environmental Research- BayCEER
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Biology > Chair Plant Ecology
Faculties
Faculties > Faculty of Biology, Chemistry and Earth Sciences
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Biology
Research Institutions
Research Institutions > Research Centres
Result of work at the UBT: Yes
DDC Subjects: 500 Science
Date Deposited: 12 Nov 2015 07:44
Last Modified: 12 Nov 2015 07:44
URI: https://eref.uni-bayreuth.de/id/eprint/22423