butions and growth rates are limited by high and low temperature extremes near the edges of their temperature
range and also by the average temperatures experienced. The range of daily and seasonal temperature fluctua-
tions is also an important determinant of growth range. Differences in responses of respiration rates to temper-
ature fluctuations play a major role in determining differences in growth rates among individual plants within
an allowed growth range. Temperature coefficients of respiration rate differ among species and among individ-
ual plants within a species. Plants from high latitude and high elevation sites have smaller dependencies of met-
abolic rates on temperature than plants from low latitude, low elevation sites. Temperature coefficients are her-
itable characteristics, not simply a consequence of acclimation. Not all metabolic processes have the same tem-
perature dependence, even within a single plant. For example, the temperature dependence of the CO2
production rate
in most plants differs from the temperature dependence of metabolic heat rate 
q. For dif-ferent plants,
may be greater than, equal to, or smaller than 
. Changing ratios of 
indicate changing efficiency with temperature and therefore with climate. Our measures of the temperature dependence
of respiration parameters combined with a thermodynamically based model of plant growth now provides phys-
iological explanations for the biogeographical distributions of plants. Values of
are related to the range of climates habitable by a species and can be used along with other parameters to select plants best suited for
growth within a given environment.