Drought Causes Amazon Rainforest Trees to 'Inhale' Less Carbon from the Atmosphere

For the first time ever, scientists have discovered direct evidence of the rate at which individual trees in the Amazon rainforest "inhale" carbon from the atmosphere during a severe drought. The findings could be huge when it comes to calculating how much these forests contribute to carbon capture and storage in the future.

Scientists have long suspected that drought influences how much carbon trees manage to capture and store. The extent of that influence has long remained a mystery-until now. Scientists measured the growth and photosynthesis rates of trees at 13 rainforest plots across Brazil, Peru and Bolivia, comparing plots that were affected by the strong drought of 2010 with unaffected plots.

Each of the plots contained between 400 to 500 trees. In addition, the rainforest plots that were chosen were representative of the varying climatic and soil conditions of the Amazon basin.

So what did the researches find? It turns out that while the rate of photosynthesis was constant among trees on plots unaffected by drought, rates on the six drought-affected plots dropped significantly. In addition, while growth rates of drought-affected plots were unchanged, levels of tissue maintenance and general health of trees were reduced.

"Tropical rainforests have been popularly thought of as the 'lungs' of the planet," said Christopher Doughty, one of the researchers, in a news release. "Here, we show for the first time that during severe drought, the rate at which they 'inhale' carbon through photosynthesis can decrease. This decreased uptake of carbon does not decrease growth rates but does mean an increase in tree deaths. As trees die and decompose, the concentrations of carbon dioxide in the atmosphere will increase, potentially speeding up climate change during tropical droughts."

The findings could be especially important when it comes to monitoring tropical forests and understanding how much carbon is being stored. If drought conditions worsen in the future, it's possible that more carbon dioxide may enter the atmosphere.

The findings are published in the journal Nature.

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