Hydraulic lift is the passive movement of water from roots into soil layers with lower water potential, while other parts of the root system in moister soil layers are absorbing water. This phenomenon has been observed in a relatively small number of species, but it is not restricted to these species or regions. Hydraulic lift occurs when active root systems span a gradient in soil water potential and when resistance to water loss from roots is low. Large quantities of water are lifted at night, which can provide a source of water for transpiration the following day. This process can facilitate water movement through the soil-plant-atmosphere system, especially under high atmospheric demand. Water released into the upper soil layers can be utilized by neighboring plants and may provide moisture that facilitates favorable biogeochemical conditions for enhancing mineral nutrient availability, microbial processes, and nutrient acquisition by roots. Hydraulic lift may also prolong or enhance fine-root activity by keeping them hydrated. The primary selective force in the evolution of this process may be the indirect benefits of hydraulic lift. Alternatively, hydraulic lift may simply be the consequence of roots not possessing true rectifying properties. The direction of water movement may also be downward or horizontal if the prevailing soil water potential gradient so dictates. Hydraulic lift has implications for rhizosphere processes, species interactions, and water movement in and through plant communities. The phenomenon has been observed in laboratory experiments, where water transfer between soil compartments has been demonstrated. Direct measurements of water efflux from individual hypocotyls or roots have also been reported. However, the interpretation of data from probes used to detect hydraulic lift must be careful, as signals may come from internal root water rather than from soil moisture. Hydraulic lift has been demonstrated in experiments where water transfer from roots of one plant to those of another was observed.Hydraulic lift is the passive movement of water from roots into soil layers with lower water potential, while other parts of the root system in moister soil layers are absorbing water. This phenomenon has been observed in a relatively small number of species, but it is not restricted to these species or regions. Hydraulic lift occurs when active root systems span a gradient in soil water potential and when resistance to water loss from roots is low. Large quantities of water are lifted at night, which can provide a source of water for transpiration the following day. This process can facilitate water movement through the soil-plant-atmosphere system, especially under high atmospheric demand. Water released into the upper soil layers can be utilized by neighboring plants and may provide moisture that facilitates favorable biogeochemical conditions for enhancing mineral nutrient availability, microbial processes, and nutrient acquisition by roots. Hydraulic lift may also prolong or enhance fine-root activity by keeping them hydrated. The primary selective force in the evolution of this process may be the indirect benefits of hydraulic lift. Alternatively, hydraulic lift may simply be the consequence of roots not possessing true rectifying properties. The direction of water movement may also be downward or horizontal if the prevailing soil water potential gradient so dictates. Hydraulic lift has implications for rhizosphere processes, species interactions, and water movement in and through plant communities. The phenomenon has been observed in laboratory experiments, where water transfer between soil compartments has been demonstrated. Direct measurements of water efflux from individual hypocotyls or roots have also been reported. However, the interpretation of data from probes used to detect hydraulic lift must be careful, as signals may come from internal root water rather than from soil moisture. Hydraulic lift has been demonstrated in experiments where water transfer from roots of one plant to those of another was observed.