Interactive effects of global change factors on terrestrial ecosystem productivity are treatment length and intensity dependent

1. Background/Question/Methods: Individual effects of co-occurring global change factors on ecosystem productivity have been widely studied; however, their interactive effects are poorly understood. Here, we conducted a global meta-analysis to examine the interactive effects on ecosystem productivity of global change factors including elevated [CO₂], warming, nitrogen addition, irrigation, drought, and changes in species diversity.
2. Results/Conclusions: Of the factors studied, six pairs had additive and two pairs had synergistic interactions. Importantly, the synergistic interactions between elevated [CO₂] and nitrogen addition became additive at high nitrogen addition rates, whereas the synergistic interactions between irrigation and warming diminished at higher temperatures. Over time, the additive effect between elevated [CO₂] and increased species richness switched to synergistic. Our results suggest that global change factors interactively affect ecosystem productivity, and the interaction type shifts with experimental duration and treatment intensity. Context-dependent nature of interactive effects indicates that global change effects are much more complex than we previously thought.