Response of maize leaf photosynthesis to low temperature during the grain-filling period

The response of dry matter accumulation and leaf photosynthesis in maize (Z ea mays L.) to low temperature has been documented during early phases of d evelopment, but little is known about the low-temperature response of maize during later phases of development. Studies were conducted in 1999 at the Cambridge Research Station, Ontario, Canada, to quantify the effect of low night temperature during grain filling on leaf photosynthesis of short-seas on maize hybrids. Plants were grown in a hydroponic system in the held with plants in the low-night temperature treatments exposed to 4 degrees C from late afternoon (17:00 h) to the next morning (9:00 h). Plants of three mai ze hybrids (i.e., an older hybrid, Pride 5, and two more recent hybrids, Pi oneer 3902 and Cargill 1877) were exposed to one night or three consecutive nights of 4 degrees C at weekly intervals from tasseling to 6 weeks after silking. Carbon exchange rate (CER) was measured at 10:00, 12:00, 14:00, an d 16:00 h on the second leaf above that subtending the topmost ear. Dark-ad apted chlorophyll fluorescence (F-v/F-m) was measured at 9:00 h at 6 weeks after silking. Leaf CER of control plants declined almost linearly from abo ut 50 mu mol m(-2) s(-1) at tasseling to about 20 mu mol m(-2) s(-1) at 6 w eeks after silking with the rate of decline in the older hybrid approximate ly two times greater than that in the two newer hybrids. No trend in the re duction in cold-stressed leaf CER relative to the field-grown control was a pparent from tasseling to 6 weeks after silking. Reduction in CER was great er during the morning than during the afternoon after exposure to 4 degrees C and the reduction in leaf CER increased from 19.4% after one night, to 2 5.8% after two nights, and 30.2% after three nights. Mean reduction in leaf CER after one night at 4 degrees C differed significantly among the three hybrids and was 29.7% for Pride 5, 15.4% for Pioneer 3902, and 13.5% for Ca rgill 1877. The reduction in leaf CER due to low night temperature was asso ciated with a reduction in leaf chlorophyll fluorescence. In conclusion, ma ize hybrids differ significantly in leaf CER response to cold night tempera ture during the grain-filling period. (C) 2000 Elsevier Science B.V. All ri ghts reserved.