Bermudagrass Response to Chilling Temperatures as Influenced by Iron and Benzyladenine

Chilling temperatures (10 to 15 °C down to 0 °C) disrupt photosynthesis, reduce growth, and discolor bermudagrass (Cynodon spp.) turf. We studied the effects of chilling in controlled environments on the CO₂ exchange rate (CER), total nonstructural carbohydrate (TNC) content, amylolytic enzyme activity (AEA), chlorophyll content, and turf color in two bermudagrasses to determine the influence of iron and benzyladenine (BA) upon these parameters. Grasses were grown on a Frederick silt loam (clayey, kaolinitic mesic Typic Hapludult) at pH 5.7 with 4.8 g N m⁻² month⁻¹. Daytime CER of ‘Midiron’ and ‘Tifgreen’ declined 71 and 82% and night-time CER declined 55 and 52%, respectively, during 4 d at chilling (10/7 °C day/ night) temperatures. Midiron CER was 70% of the original daytime rate at 30 °C but Tifgreen returned to within only 27% when returned to 30 °C for 2 h after the chilling treatment. In contrast, night-time CER fully recovered. Tifgreen's low daytime CER was associated with a 25% decrease in chlorophyll content, 60% decrease in AEA, and 160% increase in leaf TNC during chilling. Midiron chlorophyll content was unchanged, AEA decreased 30%, and leaf TNC increased 88% during chilling. The Fe treatments had similar prechill daytime CER. However, 120 mg Fe m⁻² as FeDTPA maintained a 23% higher average daytime CER than 0 mg Fe m⁻² after chilling and following recovery from chilling. Night-time CER before and after the chilling regime was not affected by Fe. Average night-time CER was 28% higher for the 120 than the 0 mg Fe m⁻² treatment after the recovery period. Leaf TNC accumulation was similar for the Fe treatments. Darker green turf color was observed for 120 than for 0 mg Fe m⁻² after the chilling period although no difference in chlorophyll content occurred. Daytime and night-time CER, chlorophyll content, TNC, and color scores for the 0 and 12.4 mg BA m⁻² treatments were similar at each temperature regime. Although chlorophyll loss and TNC accumulation in leaves are associated with photosynthetic inactivity in chill-sensitive bermudagrasses, disruption of carbon partitioning and utilization probably contribute to reduced growth and turf quality of bermudagrasses at chilling temperatures. Foliarly applied Fe may facilitate the maintenance of physiological activity and more desirable turf quality of bermudagrass exposed to chilling temperatures.