Rising atmospheric CO2 is greatly altering the productivity and composition of plant communities across the world. Increasing CO2 stimulates the photosynthesis and growth of plants but the ability to respond to CO2 differs significantly across species and functional groups. For grass-dominated ecosystems, such as grasslands and savannas, which together cover 25% of the world's vegetated terrestrial area and have vast socio-economic value, rising CO2 is a particularly significant threat. Elevated CO2 is contributing to significant grassland community changes, such as the substantial increases in C3 tree and shrub densities seen in C4 grass-dominated ecosystems across the world in recent decades. However, changes in community dynamics are not solely down to the CO2-responsiveness of plant species, but also their competitive ability. How these two aspects of plant performance under a changing climate interact to determine community changes is unclear, making the future of grassland communities, and their associated array of ecosystem services and biodiversity, difficult to predict.

Predicting grassland community interactions in future high CO2 climates requires an understanding of the interactions between a plant’s capacity to respond to eCO2 and its competitive ability. Researcher and Manager, Dr Sarah Raubenheimer, along with Prof Peter Reich and other colleagues, address this question by utilizing experimental data from grassland ecosystems around the world to assess how plant performance is influenced by its ability to respond positively to eCO2 stimulation and its competitive ability relative to its neighbors. We confirm that the high plant CO2 stimulation expected from theoretical models and experiments which exclude competition are unlikely to be seen in field scenarios with strong competitive dynamics and that CO2 stimulation will not provide significant greater tolerance of competition for most species studied. Both spatial and temporal variability will play a great role in determining competitive outcomes in unstable and dynamic systems which have tree-grass mixtures.

Researchers involved: