Increasing carbon dioxide (CO2) concentrations in the atmosphere act as a fertilizer for plants, speeding their growth and altering how they use water and interact with the climate. However, an insufficient supply of nitrogen, an essential nutrient for plants, can limit the accelerated growth caused by increased CO2. U.S. Department of Energy researchers with the Massachusetts Institute of Technology's (MIT) Joint Program on the Science and Policy of Global Change with scientists at Lehigh University adapted the Community Land Model (CLM-CN) to represent how nitrogen limitation affects plant growth.
This model refinement addresses previous underestimates of plant growth from elevated CO2 in dry regions and overestimates in moist regions. These improvements strengthen the underlying terrestrial ecosystems component of MIT's broader Integrated Global Systems Model of human-Earth system dynamics.
CLM-CN simulates plant response to climate change and the resulting shifts in water supply. Plant growth affects water supply, for example, when plants grow more quickly and use more water for photosynthesis. This leaves less water in the ecosystem for other uses. Likewise, when plants grow more slowly, they use less water, leaving more water in the ecosystem as runoff or soil moisture. The interlinked relationship between plant growth and water means that an accurate estimation of plant growth is essential for simulating interactions between ecosystems and the rest of the climate system and for improving the understanding of regional hydrology. Previously, the CLM-CN had overestimated plant activity compared to historical observations, especially in tropical forests. When researchers added the capacity to consider nitrogen limitations, the new simulations showed that growth still increased as atmospheric CO2 increased, but that the global mean increase in growth was 18.3% less than when nitrogen limitation was not considered.
This study was supported by the MIT Joint Program on the Science and Policy of Global Change and a U.S. Department of Energy subaward from MIT for an integrated framework for climate change assessment.
E. Lee, B.S. Felzer, and Z. Kothavala, "Effects of nitrogen limitation on hydrological processes in CLM4-CN." Journal of Advances in Modeling Earth Systems 5 (4), 741–754 (2013). [DOI: 10.1002/jame.20046]