Nonlinear, interacting responses to climate limit grassland production under global change

Significance Global environmental change involves many factors that occur simultaneously, yet they are usually studied in isolation. Here we report a long-term global change experiment that subjected California grassland to multiple individual and simultaneous changes in temperature, precipitation, carbon dioxide, and nitrogen. Our analysis revealed nonlinear and interactive effects of temperature and precipitation on grassland net primary production (NPP), which defined a ridge-shaped NPP response surface to these two variables. Added nitrogen raised the peak of the NPP response surface, and added CO 2 shifted the peak to lower temperatures. Our approach was validated by tests showing an absence of progressive effects over the years. In other ecosystems, our approach may be similarly powerful for probing the effects of multifactor global change.