Differences among commercial maize (Zea mays L.) hybrids in respiration rates of mature leaves

Total seasonal dry matter accumulation of recently released commercial maize ( Zea mays L.) hybrids is greater than that of older hybrids. Part of this difference may be attributable to lower rates of respiration among newer hybrids. The objective of this study was to determine if hybrids released between 1959 and 1995 differ in their rates of respiration of mature leaves. Early morning rates of dark respiration were compared among six hybrids, grown at two different soil nitrogen (N) levels in replicated field trials at two locations. Measurements were made over 9 or 11 weeks, beginning ≈50 days after sowing, and continuing until the onset of leaf senescence. Leaf respiration was measured as the rate of CO 2 efflux from leaf disks in a simple open-flow gas-exchange system, and was calculated on both a leaf area ( R LA ) and a leaf dry weight ( R DW ) basis. This measurement system revealed significant effects of crop age, leaf position, time of day, and N fertilization treatments on rates of dark respiration of leaves in the field. Significant differences in mean seasonal rates of R LA and R DW were detected among the six hybrids studied. The ranking of the six hybrids with respect to R DW was the same at both locations in the absence of nutrient stress due to low soil N. A strong negative correlation between R DW and total seasonal dry matter accumulation among these six hybrids indicates that a reduction in rates of leaf respiration may have contributed to improvement in agronomic performance of commercial maize hybrids grown in Ontario between 1959 and the present.