Physiological and biochemical responses of the achachairu tree (Garcinia humilis) to the combined effects of salinity and flooding

Abstract

Most terrestrial plants are sensitive to prolonged flooding or soil salinity, and exposure to the combination of these factors generally compounds the negative effects of each one considered separately. Achachairu (Garcinia humilis, fam. Clusiaceae), a tropical fruit tree from the Bolivian Amazon, is tolerant to flooding and moderately tolerant to soil salinity, but its physiological and biochemical responses to the combined effects of flooding and salinity have not been reported. This study assessed the physiological and biochemical responses of G. humilis to the combined effects of 30 d flooding and salinity levels of 4 dS m^-1. Physiological variables measured included leaf gas exchange [net CO₂ assimilation (A), stomatal conductance of H₂O (g_s), and intercellular CO₂ concentration (C_i)], leaf chlorophyll index (LCI), and the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm). Leaf and root nutrient analyses were performed to assess nutrient imbalances and the accumulation of toxic ions. Antioxidant responses, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione (GSH); reactive oxygen species (ROS); and lipid peroxidation (MDA) were also measured. The results indicate that G. humilis can tolerate the combined effects of prolonged flooding of 30 d and soil salinity of at least 4 dS m^-1, maintaining basal A and g_s levels of approximately 30%, with no evidence of physiological damage to LCI, Fv/Fm, or visible stress symptoms. While Na and Cl concentrations increased in leaf and root tissues, trees were able to maintain nutrient homeostasis within non-toxic levels. A robust antioxidant response was observed and possibly countered the potentially noxious effects of flooding and salinity.