Effects of Abiotic Stress on Respiratory Carbon Loss of Two Maize (Zea mays L.) Inbred Lines and Their Hybrid During Silking and Grain-Filling

High-yielding commercial maize (Zea mays L.) hybrids have higher seasonal dry matter accumulation (DMA) than their inbred parents, with the difference often being greater under conditions of abiotic stress. The greater DMA of high-yielding maize genotypes has been attributed in part to maintenance of higher leaf photosynthetic capacity during the grain-filling period, but it is possible that lower respiratory C loss also contributes to higher DMA. We compared the root and shoot dark respiration rates of a hybrid to those of its two parental inbred lines under resource-replete conditions, and also under conditions of shade stress, water stress, and N stress. Stress treatments applied over a 3-wk period around silking did not affect root or shoot respiration rates per unit dry weight (DW). By contrast, all three stress treatments reduced respiration per unit DW when the stresses were applied over 3 wk during the grain-filling period. By 5 wk after silking, respiration per unit DW was significantly lower in the hybrid than in either of the inbred lines, but this may have been due to greater dilution of the respiration signal by the accumulation of structural biomass and/or storage tissues in the hybrid, rather than a lower respiration rate per se. We did not find strong evidence that the hybrid benefited from fundamentally lower respiratory requirements than its inbred parents, or that the hybrid and its parental inbreds differed in their respiratory responses to abiotic stress.