Enhancing land surface models to grow perennial bioenergy crops

Miscanthus, a high-yield perennial biofuel crop, is a promising alternative to traditional annual biofuel crops. (Image courtesy of the U.S. Department of Agriculture)

The Science

Researchers project that biofuel production will continue to expand around the world. To understand the effects of this trend, scientists must accurately represent biofuel crops in land surface models. Using observations from biofuel plants in the Midwestern United States, researchers simulated two biofuel perennial plants, Miscanthus and switchgrass. The simulations indicate these high-yield perennial crops have several advantages over traditional annual bioenergy crops. They assimilate more carbon dioxide, and they require fewer nutrients and less water. This suggests these perennials are promising bioenergy crops.

The Impact

This study constitutes the first attempt to simulate perennial bioenergy crops in the Community Terrestrial System Model (CTSM). The CTSM is an important multisector model. With this enhancement, CTSM becomes one of the first land models that can evaluate the complex dynamics of biofuel expansion. The model incorporates energy, water, land, and climate dynamics, and it works at local, regional, and global scales.

Summary

This study establishes the foundation for examining the impact of extensive plantations of bioenergy crops on terrestrial hydrological and biogeochemical cycles and the surface energy balance. Researchers implemented Miscanthus and switchgrass into CTSM, formerly known as the Community Land Model (CLM), using parameters for photosynthesis, seasonal changes, resource allocation, plant decomposition, and carbon cost for nitrogen uptake. They simultaneously integrated land management practices. When the researchers validated the simulations against site?level measurements, the results demonstrated that the model was capable of capturing both overall patterns of carbon and energy fluxes and the plants' growth from leaf emergence to old age.

The perennials Miscanthus and switchgrass tend to be more productive than maize-soybean rotation and offer larger net carbon sinks as a result of their longer growing season, larger leaf areas, and above?ground biomass. Compared to annual crops, these perennials crops lead to increased transpiration, lower annual runoff, and larger carbon uptake. The model simulations suggest that with higher carbon dioxide assimilation rates and lower demands for nutrients and water, high?yielding perennial crops are promising alternatives to traditional annual crops for bioenergy feedstocks. This promise includes stabilizing greenhouse gas concentrations. It also includes the environmental conservation benefits from reducing fertilizer application, which alleviates surface water and groundwater contamination. Although the local?scale simulations shed light on the potential benefits of using these perennial grasses as bioenergy feedstocks, quantifying the consequences of their plantations at larger scales warrants additional investigation.

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Funding

This research was supported by the Department of Energy (DOE) Office of Science, Earth and Environmental System Modeling program as part of research in MultiSector Dynamics.