Clonal variation in shoot respiration and tree growth of Eucalyptus hybrids

Abstract

Respiration rate and efficiency in growing tissues are major determinants of plant growth. We measured apical shoot respiration and tree growth in 3-year-old clones of Eucalyptus camaldulensis Dehnhardt × Eucalyptus grandis W. Hill ex Maid. and Eucalyptus camaldulensis × Eucalyptus globulus Labill. Respiration was measured by isothermal calorimetry and the oxidation state of newly formed biomass was determined by elemental analysis. We found that the enthalpy change due to conversion of carbon substrate to biomass was too small for determining specific growth rate by an enthalpy balance model of respiration and growth. Negative phenotypic correlations were significant between respiration rate and basal area, height, volume, and volume growth. Genetic correlations between respiration rate and tree size or growth were mostly significant and estimates ranged from –0.55 to –1.02. Repeatability of the clone means was around 0.80 for respiration rate, 0.71–0.91 for summer growth, and in excess of 0.80 for tree size traits. The intraclass correlation for clones (within families) was 0.33 for rate of CO2 evolution and 0.45 for rate of metabolic heat evolution. Our results suggest considerable potential for altering respiration rate in breeding populations by selection, although the mechanisms linking respiration with growth require further investigation.