Biomass quality and quantity

Shawn Kaeppler is a researcher at the Great Lakes Bioenergy Center, a DOE Bioenergy Research Center, and the University of Wisconsin Department of Agronomy. Specific to this center is a lot of work on sustainability, including work on energy balance. You may be surprised, then, to hear that Shawn’s group is working on corn stover, but they have a strong rationale for doing so. Corn is closely related to the potential biofuel perennials miscanthus and switchgrass. They work in corn because of the resources available like a sequenced genome and large germplasm sources, and will then use the knowledge they acquire to improve the grasses.
Groups within the Great Lakes Bioenergy Center and the Agronomy Department of the University of Wisconsin are working on determining how much stover can be removed from the field. Some must remain to prevent erosion and to contribute to soil carbon. There is no easy answer, as the amount you can remove depends on soil quality, slope of the field, farming practices, and more. Some areas will need to retain more stover than others.
Core to biofuel research (as with most other breeding efforts) is screening diverse germplasm for candidate genes that correlate with traits like biomass yield and ethanol potential. Shawn’s group uses three main methods: microarrays in specific tissues, QTL analysis, and searching for candidate genes directly.
Specific traits under analysis fall under biomass quality and biomass quantity. Quality traits include using ruminant digestibility parameters because these qualities seem to be quite related to biofuel production, and provide an overall picture rather than focusing on one biochemical pathway. Quantity traits include stalk diameter and internode length.
One trait that might be related to quality is vegetative phase change, which refers to the time when juvenile tissues transition to adult tissues. Phase change timing is a trait susceptible to selection. This research addresses how timing differentials are inherited and whether having more juvenile tissue positively effects biomass quantity and quality. They found no relationship between the time of phase change and digestibility of the whole plant (without grain), however there is a relationship (although not significant) between the proportion of leaves that are still juvenile and digestibility. Overall, it seems that increasing juvenile tissue does not increase digestibility and also reduces yield because the tissue is more susceptible to disease and insects, and may senesce before harvest. This is good to know, because researchers can move on to traits that do affect digestibility / biomass quality.
Candice Hansey is a student of Shawn Kaeppler at the University of Wisconsin studying biomass quality. Her work answers the question: how can we measure ethanol potential? Simultaneous saccharification and fermentation is a great method, but very low throughput (takes a whole day to do 15 samples). Instead, they use established methods to measure forage quality (digestibility). The samples are put into a packet of filter paper, weighed, then subjected to a succession of different solvents that dissolve different fractions of the samples which then leave the filter packet. For example, the last solvent is 72% sulfuric acid which dissolves everything except acid-insoluable lignin. With this method, they can determine what percentage of each sample is lignin, carbohydrate, etc. Candy has screened different plant parts at different levels of maturity to see which might best predict the digestibility of the total adult plant. Unfortunately, the most predictive tissue was the stalk at developmental phase R6, but dissecting adult plants is a hassle. She determined that whole plant analysis is the best way to screen for digestibility.
These projects are great example of how negative results can be just as useful in moving science forward as positive results. Thanks to Shawn and Candy, we now know some areas of research that can be “checked off”, so to speak, allowing resources to be used in other areas.
Note: this post consists of my notes of Shawn and Candy’s talks at NCCC-167 2009, and was posted with their agreement.

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