Daily temperature extremes as an indicator of high temperature stress

Abstract

Theory outlining a general relationship between stress experienced by an organism exposed to supra-optimal temperatures and daily temperature extremes is discussed. It is shown that useful nomograms relating Tmax, Tmin, Tcritical, and high temperature stress can be developed and that these nomograms are not particularly sensitive to changes in daylength (caused by changes in time of year or latitude). Sensitivity of high temperature stress to changes in Tmin is also considerably less than that to changes in Tmax, suggesting that in situations where Tmin, does not vary greatly, Tmax alone can be used as an indicator of high temperature stress. Application of these concepts is illustrated by analyses of high temperature stress in pre-emergent maize seedlings. Results show that Tmax alone can account for more than 90% of the variation in the reduction of shoot length due to the occurrence of supra-optimal temperatures.