Interactive effects of global change factors on terrestrial net primary productivity are treatment length- and intensity-dependent

1. Individual effects of co‐occurring global change factors on net primary productivity (NPP) have been widely studied; however, their interactive effects remain highly debated.

2. Here, we conducted a global meta‐analysis based on 919 multifactor observations from 120 published studies to examine the interactive effects on NPP of global change factors including elevated [CO2], warming, nitrogen addition, irrigation, drought, and changes in species diversity.

3. On average, of the factors studied, six pairs of factors had additive and two pairs had synergistic interactions. Importantly, some of those interaction types changed over time and with treatment intensity. The synergistic interaction between elevated [CO2] and nitrogen addition became additive at high nitrogen addition rates, whereas the synergistic interaction between irrigation and warming diminished at higher temperatures. Over time, the additive effect between elevated [CO2] and increased species richness switched to ...