Citrus Responses under Waterlogging

Soil flooding is an adverse environmental factor of seasonal incidence associated to heavy rains, particularly in orchards on soils with poor drainage. Excess water fills empty spaces between soil particles, causing a rapid reduction in oxygen concentration and dramatic changes to the soil redox status. This alters nutrient availability, impairing root functions and, therefore, reducing water and nutrient uptake to the plant, which affects the performance of the canopy. Several plant species develop morphological adaptations to soil flooding, such as hypertrophied lenticels, aerial roots, pneumatophores or aerenchyma. However, citrus species are not among plants that develop such adaptations. Despite this, there are important differences in the ability of citrus species to withstand prolonged periods of soil waterlogging, which constitutes an important trait in citrus rootstock genotypes. In citrus, tolerance to prolonged soil hypoxia has been associated to the ability to maintain a high transpiration rate usually displayed by vigorous genotypes along with an improved antioxidant system. This book chapter discusses the physiological and biochemical responses of citrus to prolonged soil flooded and the underlying mechanisms involving hormonal signaling.