Advances in the understanding of mechanisms underlying the effects of aluminum stress on herbaceous plant physiology

Aluminum toxicity is a major factor limiting the growth of herbaceous plants in areas with acidic soils. Global soil acidification further intensifies aluminum stress-induced damage to plants. In this paper, we review the effects of aluminum stress on herbaceous plants, including the effects on agronomic traits, photosynthetic respiration, active oxygen and antioxidant enzymes, osmotic adjustment substances, root activity, and secondary metabolites. We mainly focus on the various hazards of aluminum stress with respect to herbaceous plants, but also briefly describe how low concentrations of aluminum can have a promoting effect on certain indicators of herbaceous plant growth. Aluminum stress has toxic effects on both the above- and below-ground parts of plants, causing decreases in chlorophyll content, reduced stomatal conductance, inhibition of respiration, increases in active oxygen concentrations, decreases in antioxidant enzyme activity, perturbation of osmotic adjustment, reduced root activity, and disruption of secondary metabolism. We also discuss methods that can be employed to alleviate aluminum toxicity and propose future research directions.