Crop Physiological Responses to Temperature and Elevated Atmospheric [CO2]—Climatic Zone Definitions, and Methods for Determining Where Crops Can Be Grown

This chapter discusses the quantitative reversible and irreversible stress responses of plants to temperature that are responsible for the differences in adaptation. Crop physiological responses to temperature largely determine plant adaptation to different climatic zones and seasons and can influence crop yield. Plant germination and emergence exhibit an optimal-type response to soil temperature. High daytime temperatures can have both direct inhibitory effects on vegetative growth and indirect effects, due to the high evaporative demand causing more intense water stress. Temperature affects seed germination through at least three separate processes: seeds continuously deteriorate and ultimately die, many seeds are initially dormant and once seeds have lost dormancy, their rate and extent of germination are influenced by temperature. Warm-season annuals are particularly sensitive to chilling temperatures at flowering. A unique insight into the interactive effects of high night temperature and elevated was obtained from growth chamber studies with contrasting cowpea genotypes that are either heat tolerant or heat sensitive during reproductive development.