Nutrient availability plays a crucial role in determining the overall gain or loss of carbon from forest ecosystems, according to research published online this week in Nature Climate Change. These findings challenge a basic assumption underlying most models used to estimate carbon-cycle responses to climate change.

Synthesizing the findings from 92 forests in different climate zones, Marcos Fernandez-Martinez and colleagues show that, compared with nutrient-rich forests, those growing in nutrient-poor areas use and re-release a much larger portion of the total energy, and carbon, photosynthesized by plants. In other words, nutrient-poor forests are less efficient in their use of carbon than nutrient-rich forests.

Most coupled carbon-cycle climate models used to simulate the response of the carbon cycle to climate change are based on the assumption that carbon inputs from photosynthesis have a dominant influence on the pool of carbon within a given ecosystem. These findings suggest that the efficiency with which fixed carbon is then used in the ecosystem should also be taken into account.