Carbohydrate and lignin partitioning in switchgrass biomass (Panicum virgatum L.) as a bioenergy feedstock

Abstract

Approaching switchgrass (Panicum virgatum L.) as a multifunctional energy plant, it is important to comprehensively study the composition and partitioning of organic substances in the biomass. The character of carbohydrates and lignin concentration variation was assessed in switchgrass biomass cut at two maturity stages (heading and seed filling) in the first and second harvest years. Quality components partitioning in the biomass of aboveground plant parts was examined in leaves, stems and panicles of the most productive switchgrass accessions cut at seed filling. The concentrations of lignocellulose (NDF), cellulose (Cel), sum of structural carbohydrates (holocellulose – HoCel), sum of nonstructural and structural carbohydrates (ΣCH2O) and lignin in switchgrass biomass of both plant development stages in the second harvest year were significantly higher, whereas an average hemicellulose (HCel) concentration was significantly lower compared with the respective parameters in the first harvest year. The concentrations of nonstructural carbohydrates (NSC) and their individual fractions (water soluble carbohydrates (WSC) and starch) in biomass were similar both in the first and second harvest years. The concentrations of NDF, Cel, HoCel and ΣCH2O and particularly lignin at seed filling were significantly higher compared with the respective data at heading in both harvest years. High lignin concentration (105 g kg-1 dry matter (DM)) in switchgrass biomass at seed filling in the second harvest year showed its great suitability for solid biofuel production. Considerable amount of ΣCH2O (693–742 g kg -1 DM) indicated that switchgrass biomass at this stage fits for the second-generation bioethanol production. At heading, switchgrass in the second harvest year produced quite a high NSC yield (an average 28.4 g plant-1) and low lignin output (an average 19.3 g plant-1), which is a favourable feature of feedstock for biogas production, biomass at seed filling is less suitable for that than at heading. Switchgrass plant part significantly (P < 0.01) affected the concentration of all biomass quality attributes tested, but did not affect HCel concentration. Accessions’ DM yield correlated positively with NDF (r = 0.781, P < 0.05), Cel (r = 0.882, P < 0.01) and lignin (r = 0.517) and negatively with WSC and NSC (r = −0.982, −0.959; P < 0.01).