Water uptake and hydraulic redistribution across large woody root systems to 20 m depth
Authors: Bleby TM, AJ McElrone, RB Jackson
Deep water uptake and hydraulic redistribution (HR) are important processes in many forests, savannas, and shrublands. We investigated HR in a unique cave system in a semi-arid woodland in central Texas to understand its occurrence and how deep root systems facilitate HR. Sap flow was measured in 9 trunks, 47 shallow roots and 12 deep roots of Quercus, Bumelia and Prosopis trees over 12 months. HR was extensive and continuous, involving every tree and 83% of roots, and the volume of HR was estimated at 22% of transpiration. During drought, deep roots at 20-m depth redistributed water to shallow roots (hydraulic lift), while after rain, shallow roots at 0-0.5 m depth redistributed water among other shallow roots (lateral HR). The main driver of HR appeared to be patchy, dry soil near the surface, although it is possible that water was also redistributed to mid-level depths of the profile via deeper lateral roots. Deep roots contributed up to five times more water to transpiration and HR than shallow roots during drought but dramatically reduced their contribution after rain. Our results suggest that deep-rooted plants are important drivers of water cycling in dry ecosystems and that HR can significantly influence landscape hydrology.