Triggering root proton efflux as an aluminum-detoxifying mechanism in cassava

Abstract

Aluminum (Al) is a copious element in the earth's crust, typically causing high acidity in soil-plant systems. Much research has primarily investigated adverse impacts of Al on plants, little is known about its beneficial role in enhancing mineral nutrient availability and acquisition in cassava, which is a vital economic crop relevant to human health. Herein, we examined the effect of Al levels on proton and organic acid release from the roots of two cultivars under an acid-washed sand microcosm. Consequential effects of the Al were examined on the extractability of Al and selected nutrients (iron: Fe and phosphorus: P) in the rhizosphere and bulk sands and the nutrient uptake in the plant. The results demonstrated that the highest Al level significantly demoted fresh root weight (8.53 g) but promoted the proton release from roots (2.03 μmol h⁻¹ g⁻¹ fresh weight), compared to the control treatment (11.92 g and 0.40 μmol h⁻¹ g⁻¹ fresh weight). Water-extractable Al and Fe concentrations in the rhizosphere sand were higher by 188–276 % and 201–291 %, respectively, than bulk sand in the highest Al level. The moderate Al levels (<50 μmol Al L⁻¹) also increased Fe accumulation in the plant, elaborating on the beneficial role of Al in enhancing Fe acquisition. The main organic anions (oxalate and tartrate) released from the roots were cultivar-dependent. Our study highlighted that moderate Al levels showed the benefits of Al in promoting proton release from roots, enhancing Fe availability in the rhizosphere zone, and Fe acquisition in the cassava plant.