Abstract ID: 9

Progressive increases in Amazon rainforest leaf dark respiration over five years following an experimentally imposed drought.

Increases in emissions of carbon dioxide (CO2) from the Amazon rainforest associated with increasingly frequent and severe drought event could accelerate the rate of global climate change. One rarely measured but important source of CO2 from the Amazon is leaf dark respiration (Rldark). Therefore, this study compared Rldark from trees on a one-hectare rainforest plot where approximately 50% of incident rainfall had been excluded (through-fall exclusion or TFE plot) with trees on a Control plot. Measurements taken before and for five years after imposition of the TFE treatment showed a progressive decline in the total amount of respiring foliar tissue, quantified as leaf area index (LAI) from 5.50 (pre-treatment) to 4.25 m2 m-2 (January 2007), but a consistent and significant increase in Rldark per unit leaf area from 0.53 (pre-treatment) to 0.86 μmol m-2 s-1 (January 2007). After five years of the TFE treatment, the net product of these two opposing changes was that estimated total annual nighttime foliar carbon (C) emissions from the TFE plot forest were 2.6 t ha-1 (36 %) more than forest on the adjacent Control plot, which had shown no clear change in either LAI or Rldark over the study period. We conclude that the magnitude of the drought-induced increase in foliar CO2 emissions recorded in this study is potentially sufficient to offset current estimates of the Amazon forest C sink, and alter model predictions of drought impacts upon net ecosystem exchange (NEE) of CO2 across the Amazon rainforest.

Session:  Carbon - Scaling carbon fluxes to the region from measurements in plots, towers, and aircraft.

Presentation Type:  Oral