Plant Architecture, Tolerances to NaCl and Heavy Metals May Predispose Tragus racemosus to Growth Around Motorways

Tragus racemosus often grows in close proximity to motorways. The aim of this work was to determine whether the seeds of the species can grow under salt (NaCl) stress, how the plants are able to accumulate heavy metals and what plant architecture prerequisites they have for spreading. It was found that the structure of the plant consists of a single rosette of the first order, from which shoots of the first order develop, on which rosettes of the second order grow, and this is repeated modularly. Higher-order rosettes can produce their own root systems. Research on this species revealed its small salt and heavy metal tolerances during germination and early development. The concentration of metals in the above-ground parts of plants was of the following rank: Fe >> Zn > Ni ≥ Pb > Cu; for soil, it was Fe >> Pb > Cu > Ni. The plant germinates successfully and grows in environments containing NaCl up to 0.50% (including solutions of 0.12% and 0.25%). However, higher salt contents of 0.99% and 1.96% proved lethal for seed germination. This tolerance to salt explains why T. racemosus commonly grows along motorways where winter road maintenance involves the application of salt. These adaptations give the species a competitive advantage in these human-modified environments. Furthermore, T. racemosus turned out to be a possible Ni hyperaccumulator.