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 (J_v) 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%.