Variety Interacts with Space and Time to Influence Switchgrass Quality.

Efficient conversion of biomass crops to energy requires an understanding of plant quality, including cell wall and mineral composition.  We compared key quality parameters of two leading switchgrass (Panicum virgatum L.) varieties, lowland ‘Kanlow’ and upland ‘Cave-in-Rock’, over two growing seasons and across five landscape positions.  We found plant mineral composition (nitrogen (N) concentration ([N]) and ash concentration ([ash])) was influenced more by landscape position while plant cell wall components were affected more by year of growth.  Switchgrass at the bottom of the hill slope in the floodplain position was “dirtier”, containing minerals known to contaminate biochemical and thermochemical pathways.  These overall results were supported by nonmetric multidimensional scaling (NMS) analysis, wherein two ordination axes together explained most of the variation in the data (r²=0.86).  Generally, our study shows varietal, temporal, and spatial variation in quality of two well-characterized, traditional, switchgrass ecotypes. While considerable work has focused on breeding for improved quality and regional-scale environmental effects, our results indicate that variety also significantly interacts with subfield-scale environmental and interseasonal effects. Future work should clarify overarching spatial and temporal effects on switchgrass quality, thus informing testing of genetics × field-scale environmental interactions.