Temporal arsenic form changes dynamics and accumulation patterns in Tilia cordata Mill. seedlings: Insights into metalloid transformation and tolerance mechanisms in trees

Arsenic (As) remediation is challenging due to the complex nature and the persistence of these metalloid compounds. While it may seem that differences between As forms influence have been extensively described, new findings challenge the previously accepted knowledge, particularly for woody plants. Therefore, this study focused on 2-year-old Tilia cordata Mill. seedlings early (0, 2, 4, 12, 24 h) and late (3, 7, 12, 18, 25, 33 days) responses during growth under: As(III), As(V) or dimethylarsinic acid (DMA) (0.3 mM). Time-dependent transformations of As forms, distribution in plants, and microbiological characteristics (actinobacteria, bacteria, fungi, enzyme activity) were investigated.
The highest increase in total As content was observed in plants exposed to As(V) and As(III). Dynamic metalloid form changes in the solution and tree organs were indicated. The most phytotoxic was DMA. This form was the main factor limiting the growth and effective accumulation of As. Despite experimenting in hydroponics, microorganisms played an important role in As form transformations, suggesting the potential for microbial-assisted dendroremediation strategies. The study confirmed that trees can convert more toxic forms into less toxic ones (e.g. As(III) to phytochelatins - As(III)-(PC3)), whose presence in roots seedlings exposed to As(III) and As(V) has been identified. The formation of hydrophobic forms (e.g. dimethylarsinoyl lipid) in the roots of seedlings grown under As(V) was confirmed. It is the first discovery for trees, previously observed only in bacteria and algae.
The dynamics of metalloid form changes indicated that T. cordata transforms As forms according to their needs, which may give tree species an advantage in phytoremediation techniques. It holds great promise for the potential of dendroremediation.