Effect of selective logging on the isotopic composition of respired CO2 in the Amazon region, Brazil
Abstract
Several lines of evidence suggest an existence of a 1-2 Gt carbon sink in the terrestrial biosphere. Tropical forests account for 30-50% of terrestrial productivity and the Amazon Basin is the largest contiguous rainforest region, suggesting that an understanding of the controls of gas exchange in Amazonia rainforests is central to understanding the global carbon cycle. Stable isotope ratio analyses (13C, 18O) of atmospheric CO_2 provide useful information regarding the balance between photosynthetic carbon gain and respiratory carbon loss in rainforest ecosystems and of the stomatal constraints on photosynthetic gas exchange. We show that the carbon isotope ratio of the respired CO_2 (δ13C_R) of ecosystem respired CO_2 in primary rainforests is dynamic (dominated by labile fast cycling compounds) with variation of about 3 ppm in response to changes in hydrologic conditions. Furthermore, our data suggest a direct relation between logging activities and δ13C_R in a rainforest in eastern Amazonia. A shift of 4 ppm in δ13C_R was detected after logging activities had started during the 2001 dry season. During the 2002 wet season, there was an increase in ecosystem net gas exchange. Coincident with this, there was a decrease in δ13C_R consistent with a decreased stomatal limitation in this logged forest.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....4161O