Science 322, 1085–1088 (2008)


Carbon dioxide sucked up by plants during photosynthesis is accompanied by another gas that could be used to trace the captured carbon, suggests new research. Carbonyl sulphide (COS) will allow improved estimates of global photosynthetic activity, an important buffer against human-caused CO2 emissions that has been notoriously difficult to quantify.

J. Elliott Campbell of the University of Iowa and colleagues looked at measurements of atmospheric COS, which photosynthesizing plants take up in a similar manner to carbon dioxide, from an airborne experiment across the central and eastern United States during July and August 2004. They found plants drew down 4.2 times the amount of COS predicted by past models, which assumed that both photosynthesis and respiration would control COS levels in the air. The data instead matched a new model, drawn from recent laboratory experiments, in which photosynthesis alone is the main influence.

The finding that COS, unlike CO2, is not released back to the atmosphere through respiration makes the gas ideal for tracking photosynthesis, the group concludes. COS-based photosynthesis estimates could clarify the relationships between plant growth, CO2 levels and climate change, adding precision to climate models.