Wood CO2 efflux and foliar respiration for Eucalyptus in Hawaii and Brazil

We measured CO2 efflux from wood for Eucalyptus in Hawaii for 7 years and compared these measurements with those on three-and four-and-a-half-year-old Eucalyptus in Brazil. In Hawaii, CO2 efflux from wood per unit biomass declined similar to 10x from age two to age five, twice as much as the decline in tree growth. The CO2 efflux from wood in Brazil was 8-10x lower than that for comparable Hawaii trees with similar growth rates. Growth and maintenance respiration coefficients calculated from Hawaii wood CO2 efflux declined with tree age and size (the growth coefficient declined from 0.4 mol C efflux mol C-1 wood growth at age one to 0.1 mol C efflux mol C-1 wood growth at age six; the maintenance coefficient from 0.006 to 0.001 mu mol C (mol C biomass)(-1) s(-1) at 20 degrees C over the same time period). These results suggest interference with CO2 efflux through bark that decouples CO2 efflux from respiration. We also compared the biomass fractions and wood CO2 efflux for the aboveground woody parts for 3- and 7-year-old trees in Hawaii to estimate how focusing measurements near the ground might bias the stand-level estimates of wood CO2 efflux. Three-year-old Eucalyptus in Hawaii had a higher proportion of branches < 0.5 cm in diameter and a lower proportion of stem biomass than did 7-year-old trees. Biomass-specific CO2 efflux measured at 1.4 m extrapolated to the tree could bias tree level estimates by similar to 50%, assuming no refixation from bark photosynthesis. However, the bias did not differ for the two tree sizes. Foliar respiration was identical per unit nitrogen for comparable treatments in Brazil and Hawaii (4.2 mu mol C mol N-1 s(-1) at 20 degrees C).