A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Respiration from a Tropical Forest Ecosystem: An Exception to aConstant Respiration/Photosynthesis Ratio?Jeffrey Q. Chambers 1,2, (chamberj@uci.edu), Edgard S. Tribuzy 2 , Ligia Toledo 2 ,Bianca Crispim 2 , Niro Higuchi 2 , Joaquim dos Santos 2 , Antonio D. Nobre 2 , YadvinerMalhi 3 , Susan E. Trumbore 11 University of California, Earth System Sciences, Irvine CA 92697-3100, USA2 Instituto Nacional de Pesquisas da Amazônia, 3 University of EdinburghTo understand how tropical forest carbon balance will respond to global changes willrequire knowledge of individual heterotrophic and autotrophic respiratory sources, alongwith environmental factors that control variability. We measured leaf (R leaf ), live wood(R wood ), and soil (R soil ) respiration and additional environmental factors over a one-yearperiod in a Central Amazon forest. Seasonal variability was evident in R wood and R soil ,and diurnal variability was demonstrated for R leaf . R wood was positively correlated withtree diameter and growth rate, R leaf was positively correlated with leaf temperature, andR soil was curvilinearly correlated with soil water content. An ecosystem flux for R leaf andR wood was estimated by calculating a leaf area index (LAI) and stem area index (SAI)using allometric relationships derived from tree harvest data and published models.Combining these estimates with literature values for missing fluxes gave an averageecosystem respiratory flux (R eco ) of 8.5 µmol m -2 s -1 . This estimate was compared withthe above-canopy flux (F ac ) derived from eddy covariance data. Multiple regression andANOVA demonstrated that about 70% of the variability in F ac was accounted for byfriction velocity (u*) variables and the above-canopy CO 2 concentration. Definedsustained high turbulence (SHT) conditions that may permit F ac to approximate R eco wererare, accounting for only 3.3% of nighttime hours. F ac during SHT conditions was 6.5µmol m -2 s -1 , with a large 95% CI of 2.9-13.4. Using published leaf and wood productionestimates, we estimated a carbon use efficiency (CUE ag ) of 0.28. Our CUE estimateindicates a R a to gross photosynthesis (R a /P g ) ratio of 0.72, which is considerably higherthan the relative constant ratio of about 0.50 found for temperature forests. It appearsthat Central Amazon forests have a high capacity for capturing atmospheric carbon, butonly a small fraction of that carbon becomes incorporated into new tissues.