Root Osmotic Adjustment and Stomatal Control of Leaf Gas Exchange are Dependent on Citrus Rootstocks Under Water Deficit

Drought tolerance is defined by several morpho-physiological mechanisms that together improve plant development under water-limiting conditions. Previously, we found root hydraulic redistribution is one of those mechanisms for water stress avoidance. Herein, we aimed to verify the physiological mechanisms associated with root hydraulic redistribution and its consequences for leaf gas exchange and plant growth. Valencia sweet orange scions were grafted onto either Rangpur lime or Swingle citrumelo rootstock. Each plant had two root systems of the same rootstock in distinct pots, which allowed partial irrigation. Our results revealed that citrus species redistribute water under drought and this varies when comparing rootstocks, with Rangpur lime showing higher ability to redistribute water than Swingle citrumelo. For the first time, root hydraulic redistribution in Rangpur lime was associated with osmotic adjustment in well-watered roots of plants facing water deficit. Rangpur lime also presented an effective stomatal regulation of water loss and decreases in leaf transpiration likely allowed water transport to roots under water deficit. As conclusion, we found that root hydraulic redistribution, osmotic adjustment and stomatal control of leaf gas exchange are important physiological mechanisms associated with drought tolerance induced by Rangpur lime rootstock.