Aluminum effects on micronutrient uptake by annual ryegrass

Four ryegrass (Lolium multiflorum Lam.) cultivars were grown in 1/5 Steinberg nutrient solution supplemented with six A1 levels (0, 37, 74, 148, 296, or 592 umol L⁻¹) at pH initially adjusted to 4.2. Average net Fe influx was stimulated at low nutrient solution A1 levels. This stimulation was larger for more Al-tolerant cultivars Marshall and Gulf. Decreases in average net Mn and Zn influxes were brought about by increasing Al levels in the nutrient solution. The average net influx of Fe, Mn, and Zn was positively correlated with the root tolerance index (relative root yield of plants grown with and without Al added to the nutrient solution). For more Al-tolerant cultivars, increased total uptake of Fe and Cu was brought about by increased nutrient solution A1 levels up to 74 umol L⁻¹. Decreases in total uptake of Mn and Zn were generally noted with increased nutrient solution A1 levels. Percentage inhibition of total Fe, Mn, Zn, and Cu uptake was negatively correlated with the mean pH of the Al-containing nutrient solutions. The higher average net influx and the smaller percentage inhibition of total Fe uptake at nutrient solution A1 levels up to 74 umol L⁻¹ can be used as indicators in ranking ryegrass cultivars as more Al-tolerant.