Topochemical Reorganization of the Lignin–HCA–Xylan Network Governs Cell Wall Deconstructability in Space-Mutated Arundo donax L.

Efficient biomass utilization is constrained by the trade-off between the cell wall stability and deconstructability. Space-mutated Arundo donax L. (MUT) achieves coordinated improvements in both properties. Here, confocal Raman microscopy imaging, chemical composition analysis, and 2D HSQC NMR were integrated to investigate the lignin-hydroxycinnamic acid (HCA)–xylan (LCC) network. Compared with wild-type (WT), MUT exhibited altered monolignol composition and linkages, resulting in a less condensed lignin network and a more homogeneous LCC network. Raman imaging revealed that lignin, HCA, and xylan in MUT were more susceptible to alkaline treatment, particularly in compound middle lamella (CML). After acidified NaClO2 treatment, lignin and HCA were largely removed from the CML in MUT, and the cross-link network in the secondary wall extensively disassembled, accompanied by a clear reduction in co-localization regions. These findings provide a novel structural perspective for balancing cell wall stability and degradability, laying the theoretical foundation for the targeted breeding of high-quality biomass crops.