Warmer and wetter climate promotes net primary production in C₄ grassland with additional enhancement by hay harvesting

Grassland ecosystems provide essential services to society. To maintain ecosystem functions and services of grasslands under changing environments, it is critical to understand how grasslands respond and feedback to climate change. Here, we present results from a long-term (16 years) warming and clipping (to mimic hay harvesting or grazing) experiment conducted in a grassland ecosystem dominated by C₄ grasses in the Great Plains, USA. We analyzed responses of net primary production (NPP), aboveground NPP (ANPP), and belowground NPP (BNPP) to the expanded ranges of climate conditions observed in the experiment. NPP, ANPP, and BNPP all responded to the climatic variables nonlinearly, with higher degrees of nonlinearity for BNPP than that for ANPP. BNPP peaked at the optimum air temperature of 17.5–18.5°C while ANPP peaked at the optimum air temperature of 18.5–20.0°C. The optimum air temperatures for both ANPP and BNPP were higher than mean annual temperature (16.3°C) at the site. The optimum precipitation for BNPP was intermediate levels (775–1250 mm) while ANPP was maximized in wetter conditions (1250–1605 mm) compared with BNPP. Clipping significantly reduced ANPP and shifted the optimum conditions for BNPP to warmer and wetter conditions. In summary, C₄-grass dominant ecosystems have the potential to increase NPP in future warmer and wetter conditions, and clipping may amplify this positive effect in this grassland ecosystem.