Al 3+ - Ca2+ INTERACTION IN PLANTS GROWING IN ACID SOILS: AL-PHYTOTOXICITY RESPONSE TO CALCAREOUS AMENDMENTS
High aluminum (Al) concentrations as Al3+ represent an important growth and yield limiting factor for crops in acid soils (pH ≤5.5). The most recognized effect of Al-toxicity in plants is observed in roots. However, damages in the upper parts (including stem, leaves and fruits) may also be present. In addition, Al-toxicity triggers an increase in reactive oxygen species (ROS), causing oxidative stress that can damage the roots and chloroplasts, decreasing normal functioning of photo synthetic parameters. Al-toxicity may also increase or inhibit antioxidant activities, which are responsible to scavenge ROS. As result of the negative effects of toxic Al, root metabolic processes, such as water and nutrient absorption, are disturbed with a concomitant decrease in calcium (Ca) uptake. Ca plays a fundamental role in the amelioration of pH and Al-toxicity through Al-Ca interactions improving physiological and biochemical processes in plants. Ca is a useful amendment for correcting these negative effects on crops growing in acid soils. This is an agronomic practice with alternatives, such as limestone or gypsum. There is little information about the interaction between amendments and Al-toxicity in physiological and biochemical processes in crops. Thus, the main objective of this review is to understand the interactions between Al3+ and Ca amendments and their effects on the physiology and biochemical responses in crops growing in acid soils.