LBA-ECO CD-08 Tropical Forest Ecosystem Respiration, Manaus, Brazil

This low ecosystem carbon use efficiency (CUE) differs considerably from the relatively constant CUE of similar to0.5 found for temperate forests. Our R-eco estimate was comparable to the above-canopy flux (F-ac) from eddy covariance during defined sustained high turbulence conditions (when presumably F-ac = R-eco) of 8.4 (95% CI = 7.59.4). Multiple regression analysis demonstrated that similar to50% of the nighttime variability in Fa, was accounted for by friction velocity (u*, a measure of turbulence) variables.

After accounting for u* variability, mean F-ac varied significantly with seasonal and daily changes in precipitation. A seasonal increase in precipitation resulted in a decrease in F-ac similar to our soil respiration response to moisture. The effect of daily changes in precipitation was complex: precipitation after a dry period resulted in a large increase in F-ac whereas additional precipitation after a rainy period had little effect.

This response was similar to that of surface litter (coarse and fine), where respiration is greatly reduced when moisture is limiting, but increases markedly and quickly saturates with an increase in moisture.