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Isotopes provide insight in trees’ response to climate change

Key responses of conifer trees to global climate change are fluctuations in the available carbohydrates in needles. WED researchers used stable isotope signatures and carbon concentrations to infer alterations in the carbon compounds in the needles of Douglas-fir saplings as they aged. The four-year experiment examined needles grown in controlled-atmosphere mesocosms at either ambient or elevated temperatures, and elevated carbon dioxide concentrations that were depleted in the isotope 13C. Higher and lower carbon concentrations in first-year needles were indications of increased carbon available for growth in the younger needles. Similarly, fir needles in the elevated CO2 chambers also had higher nonstructural carbohydrate, however there was no consistent effect of elevated temperatures. These findings have implications for the understanding of the carbon balance in trees exposed to global climate change and for the understanding of carbon cycling in ecosystems. (Contact: D.M. Olszyk, 541-754-4397; olszyk.david@epa.gov)

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