PNNL

Abstract

The expansion of bioenergy crops is an important strategy to mitigate climate change. However, representations of key bioenergy crops are largely missing in land models, which imposes limitations to effectively quantify their biogeophysical and biogeochemical effects in the coupled Earth system. In this study, we implement two new perennial bioenergy crops, Miscanthus and switchgrass, into the Community Land Model Version 5 by modifying parameters associated with photosynthesis, phenology, allocation, decomposition, and carbon cost of nitrogen uptake and integrating concomitantly land management practices. Sensitivity analyses indicate that carbon and energy fluxes of the perennial crops are most sensitive to photosynthesis and phenology parameters. Validation of simulated fluxes against site-level measurements demonstrates that the model is capable of capturing the overall patterns of surface energy and carbon fluxes, as well as physiological transitions from leaf emergence to senescence. Compared to annual crops, the perennial crops feature longer growing seasons, greater leaf areas, and higher productivity, leading to increased transpiration, lower annual runoff, and larger terrestrial carbon uptake. With more extensive rooting systems, these crops are more drought-tolerant with more extensive rooting systems, which also contributes to enhanced infiltration and reduced surface runoff. Our model simulations demonstrate that with higher CO2 assimilation rates and lower demands for nutrients and water, high-yielding perennial crops are promising alternatives of bioenergy feedstocks compared to traditional annual crops not only for mitigating climate change through increasing terrestrial carbon uptake, but also for environmental conservation purposes by reducing fertilizer application and therefore alleviating surface- and ground-water contaminations.