Aluminum accumulation and tolerance in four Amaranthus species

About one-third of the earth's land area consists of acidic soils. The rhizotoxic Al3+ is one of the primary constraints associated with low soil pH. Various Amaranthus species are important components of the weed flora in tea plantations on acid soils in north Iran. In this study, four Amaranthus species (A. blitoides, A. retroflexus, A. cruentus, and A. tricolor) were grown under hydroponic conditions with total Al concentrations of 0, 20, 50, 200, and 400 μM corresponding to free Al3+ activity of 0, 3.75, 11.97, 60.34, and 125 μM, respectively. Low Al concentrations (20, 50, or 200 μM) stimulated plant growth, A. tricolor demonstrated the highest improvement in shoot growth (93%), whereas A. retroflexus exhibited the greatest improvement in root biomass (367%), total root length (173%), and taproot length (32%). Although the response of shoot biomass to 400 μM Al varied among species, all species were able to accumulate Al in the leaves above the critical level considered for Al hyperaccumulation (1 mg g-1 DW). Our findings revealed Al accumulation in Amaranthus species for the first time at the genus and family levels, suggesting that these species are suitable for the restoration and revegetation of acid-eroded soils.