Physiological and Biochemical Responses of Juvenile Achachairu Trees (Garcinia humilis (Vahl) C.D. Adams) to Elevated Soil Salinity Induced by Saline Irrigation

Soil salinity affects large areas of the world and results in horticultural and biodiversity losses in tropical regions. Garcinia humilis (Vahl) C.D. Adams, fam. Clusiaceae, commonly known as achachairu, is a neotropical evergreen fruit tree native to the Amazonian forests in Bolivia. Its tolerance and responses to soil salinity exclusive of other stressors and within a range of salinity levels have not been reported. This study assessed the physiological, biochemical, and morphological responses of G. humilis to different levels of elevated soil salinity induced by saline irrigation. Physiological variables measured included net CO2 assimilation (An), stomatal conductance of H2O (gs), intercellular CO2 concentration, 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, catalase, peroxidase, guaiacol peroxidase, ascorbate peroxidase, ascorbic acid, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione, and glutathione reductase; reactive oxygen species (ROS) such as hydrogen peroxide and superoxide radical; and lipid peroxidation as indicated by malondialdehyde were also measured. The results indicate that G. humilis tolerates elevated soil salinity induced by saline irrigation with an electrical conductivity of at least 6 dS m−1, which results in stress responses without fatal consequences. Soil salinity induced by saline irrigation of 6 dS m−1 reduced An and gs by approximately 50% during a 30-day period, but there was no evidence of physiological damage based on the LCI or Fv/Fm. The levels of Na+ and Cl− did not reach toxic levels, and the plants were able to prevent damaging imbalances of plant nutrients, indicating an ion-avoidance strategy. Increased antioxidant response to soil salinity induced by saline irrigation possibly prevented ROS and lipid peroxidation damage. G. humilis appears to be moderately tolerant of soil salinity induced by saline irrigation of at least 30 days at 6 dS m−1.