we created several lines of transgenic switchgrass with documented upregulation of cDNA for the PPDK gene (C4ppdk1). Photoinhibition was higher in the transgenic lines, but electron transport rates (ETR) and quantum yield of photosystem II were not inhibited by cool conditions. The higher than expected ETR under cool conditions was associated with increased non-photochemical quenching, which indicated that enzymatic reactions of photosynthesis were inhibited more by cool conditions than photochemical processes. In all except one transgenic line, most metrics of biochemical processes decreased under cool growth conditions, which resulted in significantly lower productivity under cool conditions.