Atmospheric carbon dioxide enrichment can enhance plant carbon uptake and growth, thereby providing an important negative feedback to climate change. Nevertheless, current evidence in mature forests shows no apparent tree growth under carbon dioxide (CO2) enrichment, even though photosynthetic uptake of atmospheric CO2 increases. But then where does the extra carbon go? Jiang and colleagues track the fate of carbon in a mature forest using data from four years of ecosystem-scale Free-Air CO2 Enrichment experiments. They find that the majority of the extra carbon taken up via photosynthesis was finally emitted back into the atmosphere via enhanced ecosystem respiration, with soil respiration accounting for about half of the losses. These findings suggest that CO2 fertilization in global forests may not be as effective as previously thought in mitigating climate change.
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