Response of maize leaf photosynthesis to low temperature during the grain-filling period
Introduction
In temperate regions low temperature is an important factor limiting crop development, crop growth, and crop yield. Leaf carbon exchange rate (CER) can be particularly affected (Hällgren and Öquist, 1990; Öquist, 1983; Smillie et al., 1988), with reductions of 5–80% after exposure to a cool night in sugar cane (Saccharum sp.; Grantz, 1989), peanut [Arachis hypogaea L.; Bell et al., 1994], soybean [Glycine max L. Merr.; Purcell et al., 1987], beans [Phaseolus vulgaris L.; Crookston et al., 1974; Wolfe et al., 1988], coffee [Coffea arabica L.; Bauer et al., 1990] and maize [Zea mays L.] (Aguilera et al., 1999).
Variation in the reduction of leaf CER could be attributed to genotype, environmental conditions, stage of development, or duration of the cold stress. In maize, Dwyer and Tollenaar (1989) have reported reductions in leaf CER following a single night exposure to 9.6°C ranging from 21% for the most recently released hybrid to 35% for the oldest hybrid. Fuentes and King (1989) reported a 40% reduction in leaf CER of maize grown under field conditions after exposure to two consecutive nights with minimum temperatures below 3°C. Further, the mechanism involved in the reduction of leaf CER due to low temperature is unclear, although feedback inhibition, stomatal resistance, and disruption of metabolic process have all been suggested (Thrower, 1965; Crookston et al., 1974; Larcher, 1981; Eamus et al., 1983).
Maize grain yield in Ontario can be influenced by low temperatures both early and late in the growing season. Cool temperature during the grain-filling period is a consistent threat in Ontario, with killing frost in late August or early September causing premature death and substantially reducing yield. Cool temperature effects during early vegetative stages have been extensively studied (Öquist, 1983), but there have been few studies reported for later phases of development. Moreover, when the response of maize to low temperature has been measured during later phases of development (e.g., Dwyer and Tollenaar, 1989), the timing and duration of the cold stress was not controlled. The objectives of this study were to develop methodologies to assess the impact of low-temperature stress on leaf photosynthesis during the grain-filling period of maize and to quantify effects of one or more nights of cool temperature at various stages during the grain-filling period on the reduction in leaf photosynthesis of field-grown maize.
Section snippets
Field hydroponic system and plant material
Experiments were carried out in 1999 at the Cambridge Research Station (43°39′N, 80°25′W and 376 m above sea level). A hydroponic system was established in the field as described previously (Tollenaar and Migus, 1984). In short, this system consisted of a water pump, a fertilizer injector, and plastic pipes that delivered the nutrient solution to 1000 22.5-l plastic pails filled with “turface”, a baked montmorillonite clay (International Minerals and Chemical, Blue Mountain, MS). Irrigation
Leaf CER of field-grown control plants during grain-filling period
Leaf CER of control plants declined from silking to 6 weeks after silking and rates of decline differed among hybrids (Fig. 2). Leaf CER of Pride 5 was 50–55 μmol m−2 s−1 at silking and the rate gradually decreased to 15 μmol m−2 s−1 at 6 weeks after silking; the linear rate of decline was 6.41±1.39 μmol m−2 s−1 per week. Leaf CER of Pioneer 3902 and Cargill 1877 were 45 μmol m−2 s−1 up to 2 weeks after silking and rates decreased to 30 μmol m−2 s−1 at 6 weeks after silking; the linear rates of decline were
Discussion
Differences among maize hybrids in cold tolerance during the grain-filling period can be quantified by exposing plants to low temperature during one night. In this study, we observed the following: (i) Leaf CER of non-cold stressed plants declined substantially from tassel emergence to 6 weeks after silking, but reductions in leaf CER in cold-stressed plants relative to the field-grown control did not vary greatly during this period. (ii) Reductions in leaf CER of cold-stressed plants were
Acknowledgements
We are grateful for technical assistance by A. Aguilera and helpful suggestions for improving the manuscript by two anonymous referees. Financial support, in part, by the Ontario Ministry of Agriculture, Food, and Rural Affairs; Agriculture and Agri-Food Canada through the Agricultural Adaptation Council’s CanAdapt program; the Ontario Corn Producers’ Association; Pioneer Hi-Bred Ltd.; and Novartis Seeds Inc., is gratefully acknowledged.
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