A RESPIRATION BASED DESCRIPTION OF PLANT-GROWTH RATE RESPONSES TO TEMPERATURE

The temperature dependence of metabolic rates determines how plant gro wth rates vary with temperature. This paper shows that equations on ph ysiological relations between respiration rates (i.e. rates of heat lo ss and CO2 evolution) and growth rates can be used to describe tempera ture effects on plant growth rate. Incorporating measured values of pl ant respiratory heat and CO2 rates at a few temperatures into the equa tions allows description of growth rates as a function of temperature and provides a physiological basis for understanding the effects of te mperature on growth rate. The paper presents data on cabbage (Brassica oleracea L. Capitata) and tomato (Lycopersicon esculentum Miller cv. Ace) as model cool-climate and warm-climate cultivars to illustrate ap plication of the methods in determining optimal growth climates for di fferent cultivars, accessions, and ecotypes. The respiration-based cal culations of growth rate vs. temperature yield curves for both species that are consistent with known temperature-growth requirements. We co nclude that plant responses to temperature can be accurately predicted in detail from respiration rate measurements and the growth-respirati on model. These studies demonstrate that the temperature dependence of growth rates is a function of the temperature dependencies of both me tabolic rates and metabolic efficiency, which change continuously with temperature. The ultimate cause of high- and low-temperature growth l imits is commonly not membrane phase transitions or enzyme denaturatio n as has been supposed, but is loss of substrate carbon conversion eff iciency. The results show that ''plant temperature stress'' has been m isunderstood and must be redefined because there is no ''nonstressfull temperature''.