The magnitude of hydraulic redistribution by plant roots: a review and synthesis of empirical and modeling studies

Summary Hydraulic redistribution (HR) – the movement of water from moist to dry soil through plant roots – occurs worldwide within a range of different ecosystems and plant species. The proposed ecological and hydrologic impacts of HR include increasing dry‐season transpiration and photosynthetic rates, prolonging the life span of fine roots and maintaining root–soil contact in dry soils, and moving rainwater down into deeper soil layers where it does not evaporate. In this review, we compile estimates of the magnitude of HR from ecosystems around the world, using representative empirical and modeling studies from which we could extract amounts of water redistributed by plant root systems. The reported average magnitude of HR varies by nearly two orders of magnitude across ecosystems, from 0.04 to 1.3 mm H2O d−1in the empirical literature, and from 0.1 to 3.23 mm H2O d−1in the modeling literature. Using these synthesized data, along with other published studies, we examine this variation in the magnitude of upward and downward HR, considering effects of plant, soil and ecosystem characteristics, as well as effects of methodological details (in both empirical and modeling studies) on estimates of HR. We take both ecological and hydrologic perspectives. Contents Summary 337 I. Introduction 337 II. Synthesis of the magnitudes of HR across ecosystems 338 III. Hydraulic redistribution models 339 IV. Methodological considerations affecting the magnitude of HR 344 V. Site characteristics affecting the magnitude of HR 346 VI. Plant characteristics affecting the magnitude of HR 347 VII. Conclusions 349 Acknowledgements 350 References 350