According to a new study, the increase in global temperatures may play a significant role in altering the capacity trees have to store carbon dioxide, by changing the forest nitrogen cycle.
The study, led by Jerry Melillo of the Marine Biological Laboratory (MBL), published this week in Proceedings of the National Academy of Sciences, summarises 7 years’ worth of study at Harvard Forest in central Massachusetts, wherein a section of the forest was artificially warmed to 9 degrees Fahrenheit above ambient temperature in an attempt to mimic temperatures expected by the end of this century if no actions are taken to curb the emission of greenhouse gases.
The study confirmed what others have already shown, that a warmer climate will cause faster decomposition of organic matter in the forest soil, which in turn will lead to a faster release of carbon dioxide into the atmosphere.
However, for the first time in a field experiment, this study also showed that warmer temperatures also increase the gain of carbon dioxide in trees, which will partially offset the carbon lost to the atmosphere through decomposition.
The scientists found that the increase in carbon gain is a result of the fact more nitrogen is being made available thanks to the warmer soils.
“Tree growth in many of the forests in the United States is limited by the lack of nitrogen,” Melillo says. “We found that warming causes nitrogen compounds locked up in soil organic matter to be released as inorganic forms of nitrogen such as ammonium, a common form of nitrogen found in garden fertilizer. When trees take up this inorganic nitrogen, they grow faster and store more carbon.”
While Melillo thinks that the carbon-nitrogen interactions he is studying at Harvard Forest will help us to make predictions of carbon storage in forest over the coming decades, he adds that “the carbon balance of forest ecosystems in a changing climate will also depend on other factors that will change over the century, such as water availability, the effects of increased temperature on both plant photosynthesis and aboveground plant respiration, and the atmospheric concentration of carbon dioxide.”
Source: Marine Biological Laboratory