Biogeosciences 6, 1361–1370 (2009)

When it comes to warming's effects on plants, day and night are not equal.

Shiqiang Wan and his collaborators at the Chinese Academy of Sciences' Institute of Botany in Beijing set up 36 experimental plots on an Inner Mongolian steppe. They warmed some plots only during the day, others during night-time hours only, and yet others around the clock.

Plots warmed only at night turned the steppe from a net carbon source to a net carbon sink; the extra warming overnight stimulated respiration rates, boosting the plants' daytime rate of photosynthesis and so their uptake of carbon dioxide. The effects of separate day- or night-time warming did not add up to equal the effects observed at constantly warmed plots.

Many simulations of the effects of global warming on plants look at constant temperature elevations during a 24-hour cycle, but these may not be delivering the right picture.