Responses of leaf area (LA), stomatal conductance (gs), root length (RL) and root hydraulic conductance per unit of root length (Lpunit) 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 (ΨL) by reducing gs. 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 Lpunit. Sesbania kept constant levels of gs, causing a transient reduction of ΨL. ΨL of sesbania was, then, recovered by increasing only RL, but not Lpunit, 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 Lpunit and coordination among Lpunit, RL, gs and LA in exploitation of wet-deeper soils in response to top soil dryness.
 A. Hodge, “The Plastic Plant: Root Responses to Heterogeneous Supplies of Nutrients,” New Phytologist, Vol. 162, No. 1, 2004, pp. 9-24.
 M. Hutchings and E. A. John, “The Effects of Environmental Heterogeneity on Root Growth and Root/Shoot Partitioning,” Annals of Botany, Vol. 94, No. 1, 2004, pp. 1–8. http://dx.doi.org/10.1093/aob/mch111
 A. Hodge, “Plastic Plants and Patchy Soils,” Journal of Experimental Botany, Vol. 57, No. 2, 2006, pp. 401-411.
 M. C. Drew, “Comparison of the Effect of a Localized Supply of Phosphate, Nitrate, Ammonium and Potassium on the Growth of the Seminal Root System, and the Shoot, in Barley,” New Phytologist, Vol. 75, No. 3, 1975, pp. 479-490.
 M. C. Drew and L. R. Saker, “Nutrient Supply and the Growth of the Seminal Root System in Barley. II. Localized, Compensatory Increases in Lateral Growth and Rates of Nitrate Uptake When Nitrate Supply Is Restricted to Only Part of the Root System,” Journal of Experimental Botany, Vol. 26, No. 1, 1975, pp. 79-90.
 R. B. Jackson, J. H. Manwarning and M. M. Caldwell, “Rapid Physiological Adjustment of Roots to Localized Soil Enrichment,” Nature, Vol. 344, No. 6261, 1990, pp. 58-60. http://dx.doi.org/10.1038/344058a0
 M. M. I. van Vuuren, D. Robinson and B. S. Griffiths, “Nutrient Inflow and Root Proliferation during the Exploitation of a Temporally and Spatially Discrete Source of Nitrogen in Soil,” Plant and Soil, Vol. 178, No. 2, 1996, pp. 185-192.
 J. S. Sperry, J. R. Donnelly and M. T. Tyree, “A Method for Measuring Hydraulic Conductivity and Embolism in Xylem,” Plant, Cell & Environment, Vol. 11, No. 1, 1988, pp. 35-40.
 J. S. Sperry, U. G. Hacke, R. Oren and J. P. Comstock, “Water Deficits and Hydraulic Limits to Leaf Water Supply,” Plant, Cell & Environment, Vol. 25, No. 2, 2002, pp. 251-263.
 F. C. Meinzer and D. A. Grantz, “Stomatal and Hydraulic Conductance in Growing Sugarcane: Stomatal Adjustment to Water Transport Capacity,” Plant, Cell & Environment, Vol. 13, No. 4, 1990, pp. 383-388.
 M. Mencuccini and J. Comstock, “Variability in Hydraulic Architecture and Gas Exchange of Common Bean (Phaseolus vulgaris) Cultivars under Well-Watered Conditions: Interactions with Leaf Size,” Functional Plant Biology, Vol. 26, No. 2, 1999, pp. 115-124.
 K. Mekonnen, R. J. Buresh, R. Coe and K. M. Kipleting, “Root Length and Nitrate under Sesbania Sesban: Vertical and Horizontal Distribution and Variability,” Agroforestry Systems, Vol. 42, No. 3, 1999, pp. 265-282.
 M. R. Rao and M. N. Mathuva, “Legumes for Improving Maize Yields and Income in Semi-Arid Kenya,” Agriculture, Ecosystems & Environment, Vol. 78, No. 2, 2000, pp. 123-137.
 N. Sekiya and K. Yano,“Water Acquisition from Rainfall and Groundwater by Legume Crops Developing Deep Rooting Systems Determined with Stable Hydrogen Isotope Compositions of Xylem Waters,” Field Crops Research, Vol. 78, No. 2, 2002, pp. 133-139.
 N. Sekiya and K. Yano, “Water-Extraction by Split-Roots of Sesbania (Sesbania sesban) and Pigeon Pea (Cajanus cajan) Exposed to Spatially Heterogeneous Distribution of Soil Water,” Plant Production Science, Vol. 9, No. 3, 2006, pp. 191-199. http://dx.doi.org/10.1626/pps.9.191
 M. T. Tyree, S. Patiño, J. Bennink and J. Alexander, “Dynamic Measurements of Root Hydraulic Conductance Using a High-Pressure Flow Meter for Use in the Laboratory or Field,” Journal of Experimental Botany, Vol. 46, No. 1, 1995, pp. 83-94.
 K. Kimura, S. Kikuchi and S. Yamasaki, “Accurate Root Length Measurement by image Analysis,” Plant and Soil, Vol. 216, No. 1-2, 1999, pp. 117-127.
 W. Tsuji, S. Inanaga, H. Araki, S. Morita, P. An and K. Sonobe, “Development and Distribution of Root System in Two Grain Sorghum Cultivars Originated from Sudan under Drought Stress,” Plant Production Science, Vol. 8, No. 5, 2005, pp. 553-562.
 H. M. Zimmermann and E. Steudle, “Apoplastic Transport across Young Maize Roots: Effect of the Exodermis,” Planta, Vol. 206, No. 1, 1998, pp. 7-19.
 M. A. LoGullo, A. Nardini, S. Salleo and M. T. Tyree, “Changes in Root Hydraulic Conductance (KR) of Olea oleaster Seedlings Following Drought Stress and Irrigation,” New Phytologist, Vol. 140, No. 1, 1998, pp. 25-31.
 G. B. North and P. S. Nobel, “Radial Hydraulic Conductivity of Individual Root Tissues of Opuntia fiscus-indica (L.) Miller as Soil Moisture Varies,” Annals of Botany, Vol. 77, No. 2, 1996, pp. 133-142.
 G. B. North and P. S. Nobel, “Heterogeneity in Water Availability Alters Cellular Development and Hydraulic Conductivity along Roots of Desert Succulent,” Annals of Botany, Vol. 85, No. 2, 2000, pp. 247-255.
 R. B. Jackson, J. S. Sperry and T. E. Dawson, “Root Water Uptake and Transport: Using Physiological Processes in Global Predictions,” Trends in Plant Science, Vol. 5, No. 11, 2000, pp. 482-488.