Seasonal Dynamics of Productivity and Photosynthesis of Three Biofuel Feedstocks: Field Comparisons of Miscanthus X Giganteus, Panicum Virgatum and Zea Mays
Global climate change and dwindling supplies of fossil based resources have led to increasing interest in the use of plant biomass as an alternative fuel source. One of the major limitations is in the amount of land area available to meet the needs of the expanding global population. To provide enough food, feed, fiber and fuel for the projected 9 billion people who will inhabit the Earth by 2050, land use decisions must be made carefully, and should be validated by statistically rigorous data. Furthermore, improvements in plant productivity will be necessary to ensure abundant supplies to meet the above demands. This thesis aims to compare the productivity and underlying causes of variation in productivity of three candidate species which are currently or projected to be used widely in bioenergy production, Miscanthus (Miscanthus x giganteus), switchgrass (Panicum virgatum L.) and maize (Zea mays L.), using fully-replicated field trials in the Midwestern USA. A comparison of M. x giganteus and P. virgatum cv. Cave-in-Rock over a range of 7 soil types at locations across Illinois showed that M. x giganteus produces on average 2.5 times more harvestable biomass than P. virgatum; however this difference varied considerably with location. Importantly some of the highest yields of M. x giganteus were obtained on marginal soils in southern Illinois. The first comparison of seasonal dynamics of below-ground biomass of mature M. x giganteus and P. virgatum stands over three consecutive growing seasons showed that on average, M. x giganteus has nearly double the amount of below-ground biomass than P. virgatum; the difference being due to a larger rhizome but not root mass. M. x giganteus is also shown to be more effective at cycling nutrients and energy from carbohydrates stored in the rhizomes to promote above-ground growth early in the growing season and in recycling the nutrients and carbohydrates back to the rhizomes during senescence late in the growing season. Diurnal gas exchange measurements over two growing seasons showed that M. x giganteus upper canopy sunlit leaves assimilate 33% more CO 2 than P. virgatum over two complete growing seasons, and it also uses water, light energy and nitrogen more efficiently than M. x giganteus Finally, the first replicated side-by-side trials of the two species showed that M. x giganteus produces 60% more peak biomass than Z. mays over two growing seasons, and that this difference is due to the ability of M. x giganteus to produce photosynthetically competent leaves earlier and maintain them later in the growing season than Z. mays. Even though midsummer levels of leaf-photosynthesis were higher in Z. mays, these leaf level differences were more than offset by the larger leaf area and its longer duration in M. x giganteus. Collectively, these results show that M. x giganteus produces exceptional biomass yields even by comparison to Z. mays in the Midwest by being far more efficient in capturing the available light energy and outpaces P. virgatum by being far more efficient in converting that captured energy into biomass The findings show that M. x giganteus can produce and sustain exceptional biomass yields at a range of locations. It also shows that understanding the molecular basic of its ability to maintain and develop leaves at lower temperatures than Z. mays, and to achieve higher leaf-level photosynthetic rates than P. virgatum, could aid in improving the productivity and in turn decreasing the land requirements of each of these important crops.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign