Switchgrass Feedstock Composition As Influenced by Ecotypes, Morphotypes and Tissue Types.

Switchgrass (Panicum virgatum L.) is a perennial grass native to the North American tall grass prairies. It has been identified as a dedicated herbaceous crop for the production of biofuels.  Recalcitrance is considered an important constraint for feedstock quality. Leaf, stem and whole plant tissues of leafy and stemy plants of lowland and upland populations were analyzed for key feedstock traits. The two ecotypes, upland and lowland, have distinct profiles for feedstock quality and mineral composition.  In general, upland genotypes have 3% higher lignin compared with lowlands. Hemicellulose was higher in lowland compared to uplands. Plant morphotypes e.g. leafy (leaf:stem 0.74) and stemy (leaf:stem 0.48) also have significant impact on the feedstock quality. Stemy plants had higher cellulose than the leafy type in both lowland (34.1 vs. 41.7%) and upland (39.7 vs. 42.1%) ecotypes. The stemy type contained slightly higher lignin compared to leafy types (p<0.1). Lignin, hemicelluloses and cellulose concentrations were higher in stem than in the leaf tissues. The ecotypes have significant influence on mineral compositions. Lowlands had high P and K but the uplands are rich in Ca. The leafy and stemy morphotypes did not show a distinct profile for mineral compositions. Phosphorous and potassium were found in higher concentration in the stems compared to leaves. In contrast, calcium was higher, and magnesium was generally higher on the leaves compared to stems. Ash content was high in leaves. Lowland-stemy genotypes are found more desirable lignocellulosic feedstock compared to other plant types.