Hydraulic redistribution in Citrus rootstocks under drought

Hydraulic redistribution could contribute significantly to plant water balance under limiting conditions, reducing plant sensitivity to drought. We hypothesized that citrus species are able to redistribute water under drought, transporting water from a wet to a dry portion of root system. Using an unusual experimental design, ‘Rangpur’ lime and ‘Swingle’ citrumelo rootstocks were inarched into Valencia sweet orange trunk and subjected to water withholding. In a split root system, each plant was composed by two rootstocks, isolated from each other. During water deficit, only one rootstock faced low water availability while the other remained well watered. Sap flow, leaf water potential and soil moisture were monitored for 42 days. We found reserve sap flow in both rootstocks, with water being transported from the irrigated rootstock to the non-irrigated one. Nocturnal sap flow of well-watered rootstocks revealed that water redistribution continued at night, with ‘Rangpur’ lime showing higher hydraulic redistribution than ‘Swingle’ citrumelo. The ability of Citrus roots to redistribute water is genotype-dependent and may be an important physiological mechanism associated with drought tolerance in Citrus rootstocks.