Responses of Root Hydraulic Properties and Transpirational Factors to a Top Soil Drying in <i>Cajanus cajan</i> and <i>Sesbania sesban</i>

Abstract

Responses of leaf area ( LA ), stomatal conductance ( g s ), root length ( RL ) and root hydraulic conductance per unit of root length ( Lp unit ) to top soil dryness were investigated. Pigeon pea ( Cajanus cajan ) and sesbania ( Sesbania sesban ) were grown in a vertical split-root system. From sixty-six days after sowing, the top soil was dried while the bottom soil was kept wet. Pigeon pea increased LA while maintaining leaf water potential ( Ψ L ) by reducing g s . Increased transpirational demand through canopy development was compensated for by increasing water extraction in the bottom soil. This was achieved by increasing not only RL but also Lp unit . Sesbania kept constant levels of g s , causing a transient reduction of Ψ L . Ψ L of sesbania was, then, recovered by increasing only RL , but not Lp unit , in the bottom soil while suspending LA extension, suggesting that sesbania regulated only the root area to LA ratio. This study demonstrated a species-specific significance of Lp unit and coordination among Lp unit , RL , g s and LA in exploitation of wet-deeper soils in response to top soil dryness.