Respiration from coarse wood litter in central Amazon forests

Respiration from coarse litter (trunks and large branches > 10 cm diameter) was studied in central Amazon forests. Respiration rates varied over almost two orders of magnitude (1.003-0.014 g C g-1 C min-1, n = 61), and were significantly correlated with wood density (r2 adj = 0.42), and moisture content (r2 adj = 0.39). Additional samples taken from a nearby pasture indicated that wood moisture content was the most important factor controlling respiration rates across sites (r2 adj = 0.65). Based on average coarse litter wood density and moisture content, the mean long-term carbon loss rate due to respiration was estimated to be 0.13 yr-1 (range of 95% prediction interval (PI) = 0.11-0.15 yr-1). Comparing mean respiration rate with mean mass loss (decomposition) rate from a previous study, respiratory emissions to the atmosphere from coarse litter were predicted to be 76% (95% PI = 65-88%) of total carbon loss, or about 1.9 (95% PI = 1.6-2.2) Mg C ha-1 yr-1. Optimum respiration activity corresponded to about 2.5 g H2O g-1 dry wood, and severely restricted respiration to < 0.5 g H2O g-1 dry wood. Respiration from coarse litter in central Amazon forests is comparable in magnitude to decomposing fine surface litter (e.g. leaves, twigs) and is an important carbon cycling component when characterizing heterotrophic respiration budgets and net ecosystem exchange (NEE).