Effects of aluminum toxicity on physiological and leaf chlorophyll fluorescent characteristics of rubber tree seedlings.

Aluminum toxicity is common in tropical acid soils. However, its effects on rubber tree growth and latex production are still unclear. Using potted sand culture seedlings of rubber tree, the effects of different aluminum ion concentrations on physiological and chlorophyll (Chl) fluorescence characteristics were investigated. The results showed that the cell membrane permeability, free proline content, and soluble sugar content were significantly increased, while the relative water content, catalase and peroxidase activities, Chl a content, Chl maximum fluorescence yield, maximum photosynthesis efficiency and potential activity of PSII, photochemical quenching coefficient, non-photochemical quenching coefficient and photosynthetic electron transport rate were significantly decreased when the saplings were subjected to AlCl₃ treatments with concentration higher than 200 mmol·L^-1. When the AlCl₃ concentration was lower than 100 mmol·L^-1, the aforementioned parameters did not show any significant variation among different treatments for the entire duration of the experiment. These results indicated that the rubber tree could tolerate some degree of aluminum toxicity. The threshold concentration of aluminum toxicity for rubber tree seedlings would be between 100 to 200 mmol·L^-1. When this threshold was exceeded, aluminum toxicity would cause irreversible damage to rubber tree seedlings.