Hydraulic Redistribution in P. palustris Woodlands

Trees regulate water availability among their rooting strata through a nocturnal, passive transference of water known as hydraulic redistribution (HR). This study investigates HR and groundwater use differences among common canopy species in longleaf pine (Pinus palustris Mill., Pinaceae) woodlands and explores the driving environmental factors of HR. HR was estimated by sap flux of lateral roots and main stems of three mature canopy species (P. palustris, Quercus laevis Walter., Fagaceae and Quercus margarettae Ashe., Fagaceae). We used δ18O and δD of xylem water, soil water, and groundwater to determine water source use. Finally, we related HR to environmental factors (Temperature, VWC, VPD) to better understand controls of HR dynamics.Pinus palustris had higher mean water use than either Quercus species, but also redistributed significantly more as a nocturnal water subsidy. HR fluxes were inversely related with mean daily temperature and independent of shallow soil moisture. Stable isotope mixing models, based on δ18O and δD, predict all species have access to groundwater, but utilize shallow soil water when available. In systems with highly partitioned water sources, any species with access to a groundwater is likely capable of HR; however, the magnitude of HR among species significantly varies by rooting morphology.