Tests of the ability of a respiration based growth model to predict growth rates and adaptation to specific temperature conditions: Studies on Pinus ponderosa and Eucalyptus species

Calorespiratory techniques have been developed to measure dark respiration CO₂ production and heat rates in plant tissues as a function of temperature. Mechanistic equations were developed into a model relating these metabolic rate measurements to plant growth rate and carbon conversion efficiency (Hansen et al. 1994). A series of studies were conducted to systematically test the model. The 2nd law of thermodynamics was found to mandate temperature responses that are fundamental determinants of latitudinal/altitudinal species range and diversity gradients. The model was tested on an important wide ranging species Pinus ponderosa by making calorespiration measurements over a range of growth temperatures throughout a spring elongation season. This showed a strong association between calorespiration measurements, bud elongation, and ambient temperature. Thermodynamic constraints on the model indicated temperature variation has a particularly important effect on cellular energy metabolism. This was confirmed by an inverse correlation (R2 = 0.95) between diurnal temperature variation during elongation season and height growth for 17 open-pollinated families, and local and general populations of P. ponderosa on 4 plantations. Strong associations between ambient temperatures, phenology, and calorespiration rates (measured at 15 and 25°C) were found in a study of 156 trees from 17 families on 4 plantations. Data indicated that calorespiration characteristics were heritable. However, measurements would be more useful if taken over the range of growth temperatures multiple times during elongation season. This proved to be feasible with P. ponderosa. Temperature responses were consistent on native and exotic sites. Differences between trees were measured that may be indicative of adaptation to specific climatic conditions. Calorespiration measurements were made on multiple species and intra- and interspecies controlled crosses of Eucalyptus and compared with field growth data. Climatic adaptations were effectively measured. Progeny were found to have more varied temperature responses than parents. This indicates calorespiration can be used for plant selection at specific growth sites and that plants are capable of adapting to climate change more rapidly than generally recognized.