Lignocellulosic biomass of Panicum Maximum Jacq forage grass produced in simulated future climate conditions: a potential source of fermentable sugars for bioenergy

Author(s)

Emanuelle Neiverth de Freitas

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2021-12-10

Examining board members

Maria de Lourdes Teixeira de Moraes Polizeli; Fausto Bruno dos Reis Almeida; Valdeir Arantes; Eduardo de Aquino Ximenes

• Advisor: Maria de Lourdes Teixeira de Moraes Polizeli

Abstract

Biomass produced by fast-growing grasses such as the genus Panicum represents a potential source for renewable energy production in biorefineries. Given the climate change scenario, this work aimed to study the impact of future climate conditions on the bioenergetic potential of the forage grass Panicum maximum. For this purpose, a field system (Trop-T-FACE) was used to combine temperature increase and carbon dioxide enrichment to investigate the isolated and combined effect of the elevate concentration of atmospheric CO2 (eC) (600 µmol .mol-1) and the elevate temperature (eT) at 2°C more than currently temperature. Such effects were studied on the structure, chemical composition, and accessibility to enzymes, as well as on the forage grass hydrolytic performance through the application of different pretreatment methodologies and the optimization of enzymatic hydrolysis. Our work shows that changes in the chemical composition of the cell wall may play an important role in the acclimatization process of P. maximum to abiotic stresses. The treatments of elevate temperature resulted in increasements in cellulose content, Xylose: Arabinose and Syringyl: Guaiacyl ratio, and on cellulose accessibility to enzymes, moreover they led to reduction in cellulose crystallinity. These factors caused an increase in the enzymatic hydrolysis yields found in the study for unpretreated P. maximum grown under elevate temperature. Furthermore, the pretreatment process showed to have a great influence on the effects of climate change on enzymatic hydrolysis. Through the optimization and application of an enzymatic pretreatment using crude laccase from Lentinus sajor-caju, the hydrolysis yield was significantly improved and differences between climatic conditions were not noted. The organosolv and hydrothermal pretreatments (Liquid Hot Water) also resulted in a significant increase in glucan conversion. However, the results concerning to climatic conditions were different between the pretreatments. For organosolv, the group that grew under isolated elevate CO2 (eC) treatment exhibited the greatest conversion yields in all tested hydrolysis conditions, whereas for hydrothermal this increase was found just for hydrolysis in higher solid load. Therefore, our results suggest that the differences in hydrolytic performance found between biomasses grown under different climatic conditions, as well as their intensity, are dependent on the pretreatment method applied. Likewise, we observed that the elevate temperature treatment has a dominant effect over the elevate CO2 since the combined treatment (eT+eC) had similar behaviors to the elevate temperature (eT). Finally, this work shows that future climate changes can influence the structure and composition of the cell wall and, therefore, in the hydrolytic performance of the forage grass P. maximum, especially concerning untreated biomass, going beyond, and allowing us to understand the biological adaptations and assist in the decision-making of grass selection for application in biorefineries. (AU)

• FAPESP's process: 17/23989-9 - Lignocellulosic biomass of Panicum maximum Jacq. forage grass produced in simulated future climate conditions: potential source of fermentable sugars for bioenergy
• Grantee: Emanuelle Neiverth de Freitas
• Support Opportunities: Scholarships in Brazil - Doctorate