Salinity and the Hydraulic Conductance of Roots

Abstract

The effect of salinity on hydraulic conductance of intact roots of tomato (Lycopersicon esculentum Mill.) and sunflower (Helianthus annuus L.) was determined in split‐root experiments using salinized nutrient solutions. Experiments were conducted in controlled climate chambers under two or three relative humidity levels and four solution osmotic potential levels. The relationship between water flux through roots (Jv) and total water potential difference between the leaves and the root medium (Δψ) was linear, usually with a small intercept. Thus, the root hydraulic conductance (L) was not affected by salinity within the range of fluxes obtained in these experiments, with L= 0.036 mm h−1 bar−1 for tomato and L= 0.0167 mm h−1 bar−1 for sunflower. Our results agreed with theoretical analysis of coupled water and ion uptake. From Cl− and Na+ uptake data, the reflection coefficient (o) for tomato roots was calculated as 0.956, which was compatible with the near‐zero intercept. A large intercept for sunflower could not be readily explained. Relative humidity strongly affected root growth, with more rapid growth under low humidity conditions. Transpiration of sunflower plants was reduced by 20% when the relative humidity was increased from 34% to 84%, whereas transpiration in tomato was reduced 50%.

Influence of electric conductivity management on greenhouse tomato yield and fruit quality

“…A strong linear relationship (r = 0.97) between EC of the nutrient solution and tomato plant water absorption has been demonstrated [170]. For other species, it has been suggested that root permeability decreased under salt stress and might explain the reduction of water uptake [64,152], but this explanation is not conclusive for tomato grown under 0-200 mM NaCl [158,162]. Tomato fruit has a very low transpiration rate and only around 15% of the water input comes via the xylem [90].…”

Does calcium ameliorate the negative effect of NaCl on melon root water transport by regulating aquaporin activity?

“…was observed in melon roots after 3 d NaCl supply. Reductions in root hydraulic conductivity, L p , of salinized plants have been shown in several reports (Shalhevet et al, 1976 ;Munns & Passioura, 1984 ;Evlagon et al, 1990), suggesting that the osmotic concentration had negative effects on L p . However, we previously reported (Carvajal et al, 1999) that NaCl produced a decrease in the L !…”

THE STRUCTURE OF THE CUTICLE IN RELATION TO CUTICULAR TRANSPIRATION IN LEAVES OF THE HALOPHYTE SUAEDA MARITIMA (L.) DUM.

“…maritima leaves were consistent with the latter finding and showed that the effect of increasing salinity on cuticle thickness (1*6 times) was very close to that for the reduction in cuticular transpiration (1-5 times). A significant increase (1'6 times) in cuticular resistance may play a part in decreasing transpiration rates, a phenomenon frequently observed under saline conditions (Delf, 1912;Schratz, 1934;Uphof, 1940;Ashby and Beadle, 1957;Waisel, 1972;Kleinkopf, Wallace and Hartosock, 1976;Shalhevet et al, 1976;Siadat-Pour, 1978), and a decreased flux of water through the plant would significantly mitigate against excessive ion transport to the shoot.…”