Leaf Expansion Limits Dry Matter Accumulation of Salt-Stressed Maize

Abstract

Two maize (Zea mays L.) hybrids, differing in their salt tolerance (percentage of control on a dry weight basis) and ability to accumulate Na⁺ in the shoot, were treated with 80 mol m^-3 NaCl salinity or 80 mol m^-3 NaCl plus 8.75 mol m^-3 CaCl₂. Multiple harvests were performed and the interactions of salinity with time were examined with growth analysis. Relative growth rate (RGR) and leaf area ratio (LAR) were significantly reduced by NaCl salinity, but net assimilation rate (NAR) was unaffected. Supplemental Ca²⁺ improved RGR by maintaining LAR closer to control values. LAR was inhibited in the early stages of salt stress, but was not limiting growth relative to controls in later stages. Salinity also reduced the specific leaf area and leaf weight ratio, which indicates that leaf expansion and carbon allocation were altered. Differences in salt tolerance between the hybrids were small, but significant throughout the lifecycle of the plants. These differences were associated with differences in leaf elongation rates and LAR within the first 9 days of salinity.