Variations of root hydraulic conductance of Fraxinus mandshurica seedlings in different concentrations of NH4NO3 solution

Abstract

Absorbing water from soil by roots in vascular plants is an important physiological function and plays an essential role on their water balance. The root hydraulic conductance (LP) determined by radical water transport inside the root is a major influence on the shoot water status, plant growth, and development. However, a few studies have focused on the effect of different substances on LP of roots, and the role of radical water transport was poorly understood. Based on the pressure flux approach, this study used the roots of Fraxinus mandshurica seedlings with different treatments, i.e., distilled water, NH₄NO₃ solution, and HgCl₂ to determine the effect of various substances on LP of roots. The objectives are: 1) to evaluate the difference in LP occurred between distilled water and NH₄NO₃ solution with various concentrations; and 2) to examine the changes of LP under distilled water and NH₄NO₃ solution with various concentrations after HgCl₂ treatment. The results showed that LP of roots were 18.85?10 ^8 m/(s•MPa) in distilled water, 31.25 34.15?10 ^8 m/(s•MPa) in four NH₄NO₃ solutions (2, 4, 8 and 16 mmol/L), 14.69?10 ^8 m/(s•MPa) in distilled water after HgCl₂-treated, and 9.63 13.57?10 ^8 m/(s•MPa) in four NH₄NO₃ solutions after HgCl₂-treated, respectively. Aquaporins play an important role in regulating water uptake and transport in roots. NH₄⁺ and NO₃ ^ could stimulate activity of aquaporins, and LP of roots in NH₄NO₃ solution was distinctly 77% higher than in distilled water. Nevertheless, Hg²⁺ can inhibit activity of aquaporins, and and LP of roots decreased 22% in distilled water and 68% in NH₄NO₃ solution after treatment by HgCl₂ respectively. These evidences suggested that both Hg²⁺-sensitive aquaporins and ion channels existing in the protoplasm and vacuole membranes could regulate root water uptake, transport, and integral plant water balance.