rates. However, correlations between growth and respiration rates that could establish this relation are often
weak and do not explicitly include the effects of environmental variables. A respiration model that avoids these
difficulties is presented and growth rate–respiration rate relations are illustrated with data on maize seedlings.
Simultaneous determination of metabolic heat rate (
) and CO2 rate (
) as functions of temperature lead to a mathematical description of the temperature dependence of growth rate and substrate carbon conversion
efficiency (
). Results show that (a) different genotypes may have different temperature dependencies for both 
and 
, (b) a given genotype may have different temperature dependencies of 
and 
, and (c) 
may increase or decrease as temperature increases. This model can be used for rapid selection of crop plants for
increased productivity in a specified climate and leads to better understanding of interactions between genotype
and environment. We propose that respiratory properties are the characteristics of plants most closely adapted
to the environment so as to optimize survival and reproduction. Further, relative values of the temperature coef-
ficients of
and 
may be used to place a genotype into one of two major categories, i.e., plants that grow best in cool, variable temperature climates and plants that grow best in warm, constant temperature climates.