PLANT RESPIRATION RESPONSES TO CLIMATE DETERMINE GEOGRAPHIC-DISTRIBUTION

Temperature is a major determinant of the geographical distribution of plant species. Plant distributions and growth rates are limited by hi gh and low temperature extremes near the edges of their temperature ra nge and also by the average temperatures experienced. The range of dai ly and seasonal temperature fluctuations is also an important determin ant of growth range. Differences in responses of respiration rates to temperature 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 an d among individual plants within a species. Plants from high latitude and high elevation sites have smaller dependencies of metabolic rates on temperature than plants from low latitude, low elevation sites. Tem perature coefficients are heritable characteristics, not simply a cons equence of acclimation. Not all metabolic processes have the same temp erature dependence, even within a single plant. For example, the tempe rature dependence of the CO2 production rate mu(CO2) in most plants di ffers from the temperature dependence of metabolic heat rate mu(q). Fo r different plants, q may be greater than, equal to, or smaller than m u(CO2). Changing ratios of q/R(CO2) indicate changing efficiency with temperature and therefore with climate. Our measures of the temperatur e dependence of respiration parameters combined with a thermodynamical ly based model of plant growth now provides physiological explanations for the biogeographical distributions of plants. Values of q are rela ted to the range of climates habitable by a species and can be used al ong with other parameters to select plants best suited for growth with in a given environment.