Warming Experiment

The complexity of global change: Interactive effects of warming, water availability, CO2, and N on grassland ecosystem function 

This NSF funded project extends the BioCON experiment, focusing largely on a multi-factor sub-experiment that uses 48 of the original 2 x 2 m BioCON plots planted with 9 species in 1997.

The 48 plots of priority interest in this project were chosen randomly (within each of the four CO2 x N levels) from the 16 of each combination that were planted in 1997 with 9 species. Each plot was planted in 1997 with 9 species randomly selected from a pool of 16 herbaceous species representing 4 functional groups. The species pool was comprised of the C3 grasses (Agropyron repensBromus inermisKoeleria cristata, and Poa pratensis); C4 grasses (Andropogon gerardiiBouteloua gracilisSchizachyrium scoparium, and Sorghastrum nutans); herbaceous forbs (Achillea millefoliumAnemone cylindricaAsclepias tuberosaSolidago rigida); and the N-fixing legumes (Amorpha canescensLespedeza capitataLupinus perennis, and Petalostemum villosus). These plots now contain 6-7 species on average. The experiment comprises a full factorial design of 2 temperature x 2 water x 2 CO2 x 2 N treatments, but with different treatments having begun at different points in time; consisting of 3 replicates of unique temperature, water, CO2 and N treatments (Table 1).  

Table 1. Summary of the WWCON experimental design, which consists of each of 16 factorial treatment combinations (48 plots in all) employed at the 2m x 2m plot scale.

Temperature Water CO2 concentration Soil N
ambient, +2°C soil and plants ambient, low H2O (reduced by 45%) ambient, +180 ppm


In spring 2012 we began warming treatments using soil rod and infrared lamp technology. The treatment is deployed by continuously elevating growing season plant and soil temperatures by ≈1.8 °C. The 1.8 °C increase in plant and soil temperature represents the minimum warming predicted over the next century for central North America, assuming moderate to high fossil fuel emissions increases (IPCC 2007). All plots are burned approx. every other year, as was typical of these grasslands prior to settlement. Although the major focus of this project is on the new treatment plots, understanding of the main, interactive and indirect effects of each of the global change factors (diversity, CO2, N, temperature, rainfall) in BioCON will be gleaned from observations of responses of microbes, plants or other organisms in the other ≈330 plots in BioCON, each with some subset of the treatments in the full factorial experiment that is the core of this project.

This research is supported by the National Science Foundation.