Stable Isotopic Evidence for the Widespread Presence of Oxygen-Containing Chemical Linkages between α-Cellulose and Lignin in Poaceae (Gramineae) Grass Leaves

The chemical linkage between α-cellulose and lignin in plant cell walls has long been a controversial topic and crucial to devising effective strategies for sustainable biomass and bioenergy utilization. In this new contribution, we surveyed 80 Poaceae (Gramineae) species grown in tropical Hainan Island (China) to test the hypothesis that the presence of oxygen-containing chemical linkage in Poaceae species is widespread. Our innovative natural abundance oxygen isotopic analysis allowed us to infer that more than 1/3 of the species investigated has chemical (ether) linkages between α-cellulose and lignin in their leaf cell walls, with a species-specific 2–89 oxygen-containing bonds for every 1000 glucose units. However, the presence of such linkage appears to be phylogeny-dependent. On average, species of C3 photosynthetic mode are found to have more extensive oxygen-containing linkages than those of C4 photosynthetic mode. Our finding challenges the conventional view that no chemical bonds between α-cellulose and lignin are present in higher plant cell walls and calls for new strategies for further understanding of the chemical linkage between the two major constituents of cell walls. This is especially important in the context of renewed and growing interests in biomass, bioenergy, and plant cell wall structure studies.