Integrating two physiological approaches helps relate respiration to growth of Pinus radiata

Correlation methods originating in the growth and maintenance paradigm (GMP) are traditionally used to calculate a 'growth coefficient' (g) or the 'growth potential' (1/g) of entire plants. The enthalpy balance approach is usually applied to plant organs and relies on determination of both CO2 release and O-2 reduction to provide a measure of instantaneous rates of enthalpic growth (R-SG Delta H-B). Aspects of both the approaches to explore physiological mechanisms that govern enthalpic growth (variation in rates of CO2 release versus rates of O-2 reduction) were combined. Respiration and growth rates of apical buds of Pinus radiata were affected strongly by canopy position, and moderately by branching order. A linear relation between enthalpic growth and CO2 respiration explained 69% of the observed variation. Despite faster rates of growth, enthalpic growth potential (1/g(H)) was comparatively low in the upper canopy. Low enthalpic growth potential entailed comparatively low enthalpy conversion efficiency (eta(H), ratio of R-SG Delta H-B to proportional to CO2:O-2 and to carbon conversion efficiency epsilon) at large R-SG Delta H-B. Maximizing enthalpic growth requires a large capacity for O-2 reduction. Relations between R-SG Delta H-B and eta(H) could be described by hyperbolae using two parameters. One parameter, P-1, is equivalent to enthalpic growth potential (1/g(H)). New Phytologist (2008) 180: 841-852 (c) The Authors (2008). Journal compilation (c) New Phytologist (2008) doi: 10.1111/j.1469-8137.2008.02601.x.