Abstract:

Agave americana L. is a highly productive, drought-tolerant species being investigated as a feedstock for biofuel production. Some Agave spp. yield crop biomass in semi-arid conditions that are comparable to C₃ and C₄ crops grown in areas with high rainfall. This study evaluates the bioethanol yield potential of A. americana by (1) examining the relationship between water use efficiency (WUE) and plant carbohydrates, (2) quantifying the carbohydrate and energy content of the plant tissue, and (3) comparing the products of enzymatic hydrolysis to that of other candidate feedstocks (Miscanthus x giganteus Greef et Deuter, Sorghum bicolor (L.) Moench, and Panicum virgatum L.). Results indicate that (1) WUE does not significantly affect soluble and insoluble (i.e., structural) carbohydrate composition per unit mass in A. americana; (2) without pretreatment, A. americana biomass had the lowest gross heat of combustion, or higher heating/calorific value, compared to high yielding C₄ crops; and (3) after separation of soluble carbohydrates, A. americana cellulosic biomass was most easily hydrolyzed by enzymes with greater sugar yield per unit mass compared to the other biomass feedstocks. These results indicate that A. americana can produce substantial yields of soluble carbohydrates with minimal water inputs required for cultivation, and fiber portions of the crop can be readily deconstructed by cellulolytic enzymes for subsequent biochemical fermentation.

Keywords: CAM; bioethanol; biofuel; crassulacean acid metabolism; energy; miscanthus; sorghum; switchgrass.

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Tissue Composition of <em>Agave americana</em> L. Yields Greater Carbohydrates From Enzymatic Hydrolysis Than Advanced Bioenergy Crops

^{Voinovich School of Leadership and Public Affairs, Ohio University, Athens, OH, United States}

^{Department of Chemistry and Biochemistry, Ohio University, Athens, OH, United States}

^{Department of Environmental and Plant Biology, Ohio University, Athens, OH, United States}

Edited by: Karolina Heyduk, University of Hawai‘i, United States

Reviewed by: Rachel Burton, The University of Adelaide, Australia; June Simpson, Instituto Politécnico Nacional de México (CINVESTAV), Mexico

*Correspondence: Sarah C. Davis, ude.oiho@6ssivad

This article was submitted to Crop and Product Physiology, a section of the journal Frontiers in Plant Science

Edited by: Karolina Heyduk, University of Hawai‘i, United States

Reviewed by: Rachel Burton, The University of Adelaide, Australia; June Simpson, Instituto Politécnico Nacional de México (CINVESTAV), Mexico

Received 2019 Dec 13; Accepted 2020 Apr 28.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

Abstract

Agave americana L. is a highly productive, drought-tolerant species being investigated as a feedstock for biofuel production. Some Agave spp. yield crop biomass in semi-arid conditions that are comparable to C₃ and C₄ crops grown in areas with high rainfall. This study evaluates the bioethanol yield potential of A. americana by (1) examining the relationship between water use efficiency (WUE) and plant carbohydrates, (2) quantifying the carbohydrate and energy content of the plant tissue, and (3) comparing the products of enzymatic hydrolysis to that of other candidate feedstocks (Miscanthus x giganteus Greef et Deuter, Sorghum bicolor (L.) Moench, and Panicum virgatum L.). Results indicate that (1) WUE does not significantly affect soluble and insoluble (i.e., structural) carbohydrate composition per unit mass in A. americana; (2) without pretreatment, A. americana biomass had the lowest gross heat of combustion, or higher heating/calorific value, compared to high yielding C₄ crops; and (3) after separation of soluble carbohydrates, A. americana cellulosic biomass was most easily hydrolyzed by enzymes with greater sugar yield per unit mass compared to the other biomass feedstocks. These results indicate that A. americana can produce substantial yields of soluble carbohydrates with minimal water inputs required for cultivation, and fiber portions of the crop can be readily deconstructed by cellulolytic enzymes for subsequent biochemical fermentation.

Keywords: CAM, energy, bioethanol, sorghum, switchgrass, miscanthus, crassulacean acid metabolism, biofuel

Abstract

Acknowledgments

The authors thank Misako Hata, Edison Biotechnology Institute at Ohio University, and Dr. Brian McCarthy, Department of Environmental and Plant Biology at Ohio University, for the use of materials, equipment, and laboratory space to complete some of the analyses. Acknowledgment is also given to Dr. Ahmed Faik for input on an early draft of this manuscript. All GH samples were performed at the Center for Electrochemical Engineering Research (CEER) at Ohio University. The authors would also like to thank all the many folks that assisted with planting, maintaining, and harvesting the biomass crops in Athens, Ohio and Maricopa, Arizona.

Acknowledgments

Footnotes

Funding. This work was supported financially by Ohio University, Voinovich School of Leadership and Public Affairs. A grant from the Energy Bioscience Institute with financial assistance from BP and Maricopa Agricultural Center supported the cultivation of Agave americana.

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