Lower recalcitrance of internodes than nodes in “super” Arundo donax Linn: Structural insights from lignin–carbohydrate complexes (LCCs) and lignin

Arundo donax Linn., one of the most promising bio-energy crops, has garnered continual global attention due to its substantial biomass production, particularly for genetically transformed “super” variety. Elucidating the structural characteristics of the lignin-carbohydrate complex (LCC) and lignin within the primary morphological regions of “super” A. donax is crucial to enhance the industrial processing efficiency. In this study, LCC and lignin fractions were systematically isolated from the nodes and internodes of super A. donax, followed by comprehensive structural characterization. Compared to nodes, the LCC in internodes exhibited higher lignin and p-coumaric acid (PCA) content, molecular weight, and thermal stability, surpassing those found in wide-type A. donax. Both the LCC from internodes and nodes contained phenyl glycosidic bonds, phenyl ether bonds, and ester bonds, with glycosidic bonds being the predominant. Notably, the LCC in internodes exhibited reduced levels of glycosidic linkages, while the lignin present in these internodes displayed a predominance of β-O-4′ linkages (>98%), higher S/G ratio, and PCA content compared to nodes. These findings suggested a lower biomass recalcitrance in internodes than nodes, evidenced by a slightly higher enzymatic efficiency. Overall, this work provides a theoretical framework for the biorefinery applications of super A. donax.